CHDK scripting

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See also the Scripting Cross Reference Page for the complete list of CHDK scripting commands for Lua and uBASIC. And also see: and and .

Starting out

Keep these things in mind when writing your scripts:

  • Scripts may conflict with your camera if it is set to its fully automatic state. If you are having problems try setting your camera into "P" mode. When CHDK is not loaded: press the cam/movie button then the right button until P is highlighted and press SET. Also consider setting your camera to a fixed ISO value instead of AutoISO. When CHDK is not loaded: press the SET button, then scroll up to the top and right to a fixed ISO value.
  • Use any text editor to compose your scripts. Make sure it is saving the file as TEXT-ONLY. Do NOT use programs like Word or other advanced editors. These insert hidden header info and use non-standard ASCII characters for Return/Line-Feed commands, quotation-marks, and others. The simplest of text-editors will suffice, even then watch out not to use TAB for indenting. (Notepad in Windows, nano in Linux for example.) Mac users, make sure your script is in UTF-8 encoding, see this special note concerning Macs and Script Files.
  • Keep all commands in lower-case. Variables are case-sensitive (a and A are not the same).
  • (obsolete) In versions prior to 0.5.5 (SVN Changeset 524) you are limited to 8k (8192 bytes) for the size of your script - CHDK Build 119 or later. (2k (2048 bytes) in CHDK Build 116 or earlier.)
  • Be aware that not all commands work on all cameras, if you plan on sharing your script try to keep it as generic as possible unless you have a special need for the camera-specific commands. Try to also provide a more generic version so that all may benefit from it.
  • If using earlier CHDK Builds some commands listed here will not be available to you and cause errors, this tutorial will be updated as new commands and changes are made to CHDK.
  • Keep your script concise and efficient !
It takes 10ms of time for each line of your script to be interpreted by tiny uBASIC. If your script is 10 lines long this takes 1/10th of a second, 100 lines takes a full second, etc. This can greatly impact high-speed uses.
Note: This is mainly uBasic-related; current CHDK version are using some optimations for more efficient scripting.
  • If you write an interesting script, share it with the rest of us on the User Written Scripts pages so we may learn from you! Beginner script-writers can be some of the most creative!
  • Have a look to the settings in the scripting menu, there are some interesting features available like autostart, parameter sets & more...

The Script Header


The header of a Lua script is the same as on a uBASIC script, packed into a long comment - the script parser interpretes this the same way in Lua as in uBASIC.

A Sample Lua header:

rem 20080815 test script by xxx
@title test script
@param a Duration (min)/-1 disable
@default a -1
@param b Duration (sec)/n of seqs
@default b 5
@param h Endless?
@default h 0


When viewing scripts you'll often see the opening section look something like this:
@title Interval shooting
@param a Shoot count
@default a 5
@param b Interval (Minutes)
@default b 1
@range b 0 10

Let's break down what each of those lines mean and how they are used by CHDK.

@title Your Script Title

This is the title that will appear when you have the script loaded in CHDK and go to "Scripting Parameters" menu selection. It will appear under the line "----Current Script----" as well as in the lower-left corner of your viewfinder when you are in <ALT> mode. Keep your title short (24 characters or less). Otherwise the title will cover up the <ALT> label.

@param x (label)
@default x n
@range x n m
This is where you will define the beginning values of any variables used in your script. These are often used to set how many exposures you want, how long of a delay you want, how many bracketing steps you want, etc. These variables can be changed by the end-user from the "Scripting Parameters" menu items. In that sub-menu, they will appear under the line "----Script Parameters-----"
@param x (label)
The "x" in that line will be one of any lower-case latin letter from a to z. The (label) is the text string that will appear in your "----Script Parameters----" list, to let the end user know which of the variables they are changing (i.e. number of shots, how many steps, etc.).
Up to 26 @param statments, user-controllable variables, may be used in any one script.
Note: CHDK allows you to have up to 26 user-definable variables from a to z. There are a total number of 52 variables available for your use, a to z and A to Z, but the user-definable variables must be in lower-case if used for that purpose. Also be aware that lower and uppercase variables are unrelated. If you use a lower-case j for a variable, it is not the same as using J, and vice-versa.
@default x n
This optional statement sets up the default, or beginning value of your (lower-case letter) variable, where "x" is the variable from the @param statement above, and "n" is the default value to start with. This value is only used when a script is loaded for the first time.
@range x n m
Revision 1900 (dev trunk only) adds an optional '@range' option to the script handling to allow you to set the min & max allowed values for a script parameter (examples below).
If the range is set to 0..1 the parameter is displayed in the script menu as a boolean on/off toggle instead of an integer value (the actual parameter value is still an integer though).
Simple uBasic test sample (works in Lua as well):
@title Range Test
@param a A 1..12
@default a 2
@range a 1 12
@param b B 0..1
@default b 0
@range b 0 1
@param c C -12..12
@default c 0
@range c -12 12

print a
print b
print c

Note it is up to the script writer to ensure that the @default value lies within @range - this is not validated when the script is loaded.
If there is no @title command the filename of script is used.
If there are no @param commands CHDK assumes that there are three adjustable variables: a, b and c.
Remember -- when naming @param variables, use only a character from a through z.

After your default variable values have been defined here, it is good to add some lines right after this section to ensure those numbers will be used in case the user has input 0 (zero) for some value that needs to be higher (or lower). You will see this in scripts as:

if a<2 then let a=5
If your default value that you wanted the user to start out at for parameter variable a was 5, then if they left that setting at 0 (zero) or 1, then this will automatically increase that variable's value back up to 5.

After you have set up your variable parameters, then comes the brunt of your script, the part that does the actual work and tells the camera what to do, when to do it, and what buttons or commands need to be executed. Since we are working with a very small subset of the larger uBASIC programming language, it might be good to list and explain only those that are available to the CHDK script writer.

The Basics of CHDK scripting


Most of the descriptions and examples are based on the uBasic syntax.

  • In uBasic most commands expect parameters in quotation marks, separated from the command with a space char.
  • In the Lua scripting language the parameters are written in brackets, directly (without a space char) after the command.


print "Shoot"         (uBasic syntax)
print("Shoot")        (Lua syntx)

Links to a detailed documentation of the Lua language can be found on the Lua main page.


The SDM (Stereo Data Maker) uses some enhanced or modified scripting commands. Read more on the SDM documentation pages.

Logic Commands for uBasic

All programs are designed to mindlessly repeat some commands. In order to make them work in the proper order, and the correct number of sequences, they have to be contained in some simple recurring loops and counters. Testing for when some condition has been met, before it can go onto the next command, or finally end the program (script).

There are several ways this can be done in uBASIC. By using numeric counters, and loops.

The LET Command

This one is simple. If you see a command that says "let a = 2" then that's exactly what happens. It defines the value of 2 to the variable a.
This command is mostly included just for legibility. You can leave off the let command and it will still work. Example: let a=2 can be written more simply as a=2. Or this example: if z>5 then let b=0 can be simplified to if z>5 then b=0. Doing so will greatly save on script space if you have to define and redefine many variables many times.

The IF / THEN / ELSE Commands

These are used to test for the truth of a certain condition. IF something is true, THEN this takes place, ELSE (otherwise) do this if it is not true.
A simple example:
if a > 2 then goto "subroutine1"
If in your script, the variable a has been assigned to a value greater-than 2, then the script will jump to the labeled subroutine1.
if a >2 then goto "subroutine1" else goto "subroutine2"
In this case if a is NOT greater than the value of 2, your program will jump to subroutine2.
The conditional expressions allowed in uBASIC are: = (equal to), > (greater than), < (less than), <> (not equal to), <= (less than or equal to), >= (greater than or equal to)

IF / THEN / ELSE / ENDIF - Multiple Statements

Fingalo reports: "Seems to have some bug when not using the else in nested if constructs!"


if relation then

The standard single-statement if...then...else... loop still works, but it cannot be used inside the if...then...else...endif loops.

NOTE: nesting levels for all loop methods are currently set to 4 for all new constructs.

The FOR / TO / NEXT Commands

These are used to set up simple loops. You will often see them in scripts as in this example:
for n=2 to a
    sleep t
    print "Shoot", n, "of", a
next n
The first line "for n=2 to a" means that the "for / to / next" loop will run while variable-n equals the sequence of numbers of 2 up to whatever the number variable-a has been assigned to. The commands that take place in the loop are containted between the FOR statement and the NEXT statment. "next n" tells the loop to go back to the beginning "for ..." statement until the the a value has been reached.

For example:

for n=1 to 10
   print "This is line number", n
next n

This will produce the sequence of:

This is line number 1
This is line number 2
This is line number 3
This is line number 9
This is line number 10

And then that loop will end and go onto the next sequence of commands.

FOR / TO / STEP / NEXT Loops

A standard BASIC step command was added to the for/to/next commands make loops easier. Instead of using multiple lines for counters to increment numeric expressions with commands like a=a+1 or b=b-3, a simple next command may now be used.


for var=expr to expr step expr
next var

Where var can be any variable, expr can be any defined variable or math expression, and step can be any defined variable or math expression. The step value may also be negative to increment in reverse.


@title Focus Bracket Steps
@param d Near Focus (mm)
@default d 2500
@param e Far Focus (mm)
@default e 4500
@param f Step Increment (mm)
@default f 100

for x=d to e step f
set_focus x
next x


If using the default values this simple script will start out at the Near Focus value of 2500mm, increment that value by 100mm every time, shoot an image, and exit when the focus has reached or passed 4500mm.

Subroutines using GOSUB (and related GOTO) Commands and Labels


For complex programming tasks, it is often helpful to split the program into smaller subroutines that can be called with gosub and goto commands. A sub-routine can be nearly anything but it is generally used for a set of commands that will be called-up more than once. Instead of writing the same set of commands over and over again you put that code into a subroutine and then call it up from within the main program by using gosub "label" or goto "label". Subroutines are generally placed after the main code. A labeled subroutine that will be called by gosub "label" needs to end with the return comand, to tell the script to jump out of that section of code and return back to from where it was called.
GOSUB and GOTO are similar but you should refrain from using GOTO unless you know what you are doing. GOSUB will always return from a subroutine as soon as it reaches the RETURN command. GOTO does not behave this way. GOTO should only be used when you are going to jump to a section of the script one time and under special circumstances.

GOSUB and GOTO Examples

A simple GOSUB example (the subroutine's label and subroutine are in bold):
for x=1 to 10
  gosub "display"
next x

  print x
A longer example that would capture three images with increased ISO settings would look something like this:
for i=1 to 3    
  gosub "incISO"    
next i    
for i=1 to 3    
  gosub "decISO"    
next i    
  click "menu"    
  [some more clicks]    
  click "menu"    
  [some more clicks]    
An example using the GOTO command taken from an endless intervalometer script. NOTE: This situation creates an endless loop. Until you manually override, the script it will continue. This is generally considered BAD FORM! Any script should include/end-with all the commands to reset the camera to its original configuration prior to running the script, and properly end with the END command. Do not do this kind of thing, unless you have a special need for it and know what you are doing.
@title Interval Shooting Non-stop 
@param a Interval (Minutes) 
@default a 0 
@param b Interval (Seconds) 
@default b 5 
@param c Interval (10th Seconds) 
@default c 0 


if t<100 then let t=5000 


print "Interval shooting."
print "Until you interrupt it."
print "Use with caution."

sleep 1000 

  print "Shot number", n
  sleep t
  goto "shot"

Do / Until Loops

Another method of creating loops for repetitive instructions or when waiting for some condition to be true. Code within a Do/Until loop will always be executed at least once (unlike While/Wend loops)


until relation

Where relation may be any logical expression. When it is true, the loop will exit.


rem set some starting values for the variables

rem start do-loop


rem increment x by 10 each time

rem increment y by 1 each time

rem print results to viewfinder mini-console
print "This DO loop happened", y; "times."

rem repeating do-loop until x is equal to the value of 55
until x=55


While / Wend Loops

Similar to the DO / UNTIL loops. The loop will continue to execute while some statement remains true, and will end, wend (while-end), when that statement is no longer true. Unlike Do/Until loops, code within a While/Wend loop may never be run, if the test condition is already false when the While statement is first reached.


while relation


while x<200
print "The value of x is", x

This loop will increment the value of x by 25 each time and print the value of x, as long as (while) the variable x remains less-than 200


The "rem" (which stands for "remark") command is sometimes used to place a comments in a script. It is only used as a reminder for the person writing or viewing the script, like an internal note. This command is not executed nor seen when the script is run. However, keep in mind that scripts for CHDK can be only 8k (8,192 characters) in length. (Only 2k in CHDK before Build 119.) Too many REM statements can slow down your script as well as taking up valuable space.
An (overzealous) example of REM commands in a script
rem Interval shooting

@title Interval shooting
@param a Shoot count
@default a 10
@param b Interval (Minutes)
@default b 0
@param c Interval (Seconds)
@default c 10

rem Calculate 1000ths of seconds from variables


rem Sets some default variables to initial values
if a<2 then let a=10
if t<1000 then let t=1000

rem Print total duration of session in viewfinder

print "Total time:", t*a/60000; "min", t*a%60000/1000; "sec"

rem Delay actual shooting so they can read the above print statement.

sleep 1000

rem Start actual camera operation in a loop

print "Shoot 1 of", a
for n=2 to a
    sleep t
    print "Shoot", n, "of", a
    rem This takes the actual exposure.
next n

rem Ends this script

REM statements can always be removed from a script if you feel there are too many or unneeded. Removing a rem line will not impact the operation of the script in any way (other than speeding it up and using up less memory space).

Math Expressions in uBASIC

+   Addition
-   Subtraction
*   Multiplication
/   Division
%   Remainder (explanation see below)
<   Less Than
>   Greater Than
=   Equal
<=  Less Than or Equal   (CHDK Build #144 or later)
>=  Greater Than or Equal   (CHDK Build #144 or later)
<>  Not Equal   (CHDK Build #144 or later)
&   And
|   Or
^   Xor

Most of the expressions are easy to understand, but the % (remainder) operation might like a short explanation.

Example: Let's say you have computed a number to equal how many seconds something will take for a duration. Such as s=(some math expression) Where s is being assigned the number of seconds computed.
In math it's called "modulo".
Now you want to display that as minutes and seconds. You will need a print statement such as:
print "Total Time:" , s/60; "min", (the remainder of s/60); "sec"
There is a very simple way to do this using the % command. Think of % as "the remainder of s being divided by". So all you need to do is have this print statement:
print "Total Time:" , s/60; "min", s%60; "sec"
If s had the value of 328 seconds, then this would print out to
Total Time: (328/60)=5 min (the remainder of 328/60)=28 sec
or more simply
Total Time: 5 min 28 sec

Some further notes:

<   Less Than
>   Greater Than
=   Equal
<=  Less Than or Equal
>=  Greater Than or Equal
<>  Not Equal

are relational operators. In "if" statements, only single relational operators are allowed. This means, you can't have something like "if a<2 and b>3 then...". Strike-out portion no longer applicable to build #144 or later.

&   And
|   Or
^   Xor

are bitwise operators, not logic operators. (The logic operators of and, or, and not have been added to CHDK build #144 or later.) Example use of the bitwise &, |, and ^ binary operators are:

print e

will return "7".
5&3 will result in "1"
5^3 will result in "6"
For an explanation refer to bitwise operators

Logical Operators: AND, OR, NOT in uBASIC

not	logical not (best to use in form with parentheses ie. not (expression),
and	logical and
or	logical or

Priority for evaluation order has been updated so expressions like

if a=1 or b=3 and c>4 or d<>7 then ...

are being correctly calculated, although one would preferably use parentheses just to understand what is being calculated.

Also priority for "&" and "|" has been changed the same way.

NOTE: Multiple relational operators are allowed!

Common scripting commands


This prints whatever text follows the statement, to your LCD or EVF display in the mini-console area (see firmware usage) while the script is running.
Syntax: print "25 characters of text"
You are limted to 25 characters being displayed in any one line of text. You may also include the values of variables or integer-equations in your print statement.
rem Print total duration of interval to viewfinder

print "Total time:", t*a/60000; "min", t*a%60000/1000; "sec"

sleep 1000

rem Start actual camera operation in a loop

print "Shoot 1 of", a
for n=2 to a
    sleep t
    print "Shoot", n, "of", a
next n
Note that the comma (,) is replaced in the output with a space while a semicolon (;) results in no whitespace
print "C","H","D","K"
print "C";"H";"D";"K"
Will result in


Whatever the script prints on the mini-console screen is also written to file '/CHDK/SCRIPTS/PR_SCREEN.TXT' '/CHDK/LOGS/LOG_N.TXT'[1].

First call is either,

print_screen 0 The text is appended to the last file. If the file was there already, the text is written at the end and the older text is not removed.

print_screen 1 The text is written to "A/CHDK/BOOKS/PS00000.TXT" "/CHDK/LOGS/LOG_0001.TXT"[1]. The new text overwrites any existing text in the file if there was any .

print_screen N The text is written to the next file number. The file number cycles between 0 and N-1. If the resulting file number is 5, then the text is written to file "A/CHDK/BOOKS/PS00005.TXT" "/CHDK/LOGS/LOG_0005.TXT"[1]. The file number of the last written file is kept in file "A/CHDK/BOOKS/PS_COUNT.TXT". Delete the file to reset the counter.

(The print_screen N statement is not implemented in the Allbest builds ! )

print_screen 0 turns off writing to the file and print_screen 1 turns it back on.


@title printscreen test 

@param a None 
@default a 0 

@param c mode: 0-append, 1-replace, other-modulo c 
@default c 1 

print_screen c 
print "START "c 
print_screen 0 
print "Not written to file" 
print_screen 1 
print "This should be written to the file." 
print "a="a 
print_screen 0 


cls stands for "Clear Screen". This is used to clear the mini-console screen from any "print" statements in an easy way. Instead of having to issue 5 command lines of print " ", you just need to issue this one small cls command.


This pauses the script to allow some action to take place, or to delay when the next action should occur.
Syntax: sleep x
Where x is any variable or whole number. The value is in 1000ths of a second.
Example: sleep 1500 means to pause for 1.5 seconds.


This command causes a CHDK script to leave <Alt> mode while running. Note that the uBASIC version of this command expects a single parameter (which is not used). The correct uBASIC syntax is
  exit_alt 0


This command causes a CHDK script to re-enter <Alt> mode while running (typically after having used the exit_alt() function). Available in Lua only.


---> should be moved to other keyb related command section !

Also added a varation of the is_key statement, so is_key can be used as:

if is_key "set" then goto "continue" 

And also as:

k = is_key "set"

The original statement version (example below) may still be used.

is_key k "set" 
if k=1 then goto "continue" 

The main reason for this new 'is_key option and other loop methods is that you can now more easily make key-press detection loops. Such as:

  if is_key "right" then gosub "r_label"
  if is_key "left" then gosub "l_label"
until is_key "set"

rem begin r_label subroutine
rem begin l_label subroutine


This should be the last line of every uBASICC script. It tells the script to cease all operations and return camera control back to you. Before ending a script, it is good-form to always reset any camera settings that the script took control of during initialization of your routine or during. So that the end user doesn't have to undo all the keypresses and menu changes that the script created.

Motion Detection

Note 1: There has been much discussion on the proper ways to use this sometimes-confusing and highly adaptable and user-configurable feature. A lengthy discussion on the new CHDK Forum on how to get the fastest reaction times for lightning photography has shed some light on the subject (pun not intended). For further clarification on the best ways to implement some of the timing controls, see this post in the "Motion Detection Too Slow?" discussion thread. Which also includes a script optimized to obtain the fastest detection speed possible by using 2 different methods (both available in the same script). The MD routine has been reworked for some cameras so the internal "immediate shoot" option is now lightning-fast (literally). This change will probably be added to all new future builds (note added 2008-02-07 c.e.).
Note 2: Hints and tips for usage have been scattered all over the net, a new "Motion Detection Settings" page was created to try to assemble some of the best tips. If you can add to it or help clarify it, please do so. The page linked in the strike-out comment is wholly irrelevant as-is. The info there was taken out of context from another post discussing a script that uses the md-routine, and has no information about the md command itself. A good idea poorly implemented. If you would still like to create a more concise and clear explanation of all of the md parameters and usage, with sample script explanations, feel free to use that page, Delete everything on it if you have to and start from scratch. Otherwise, don't even bother reading it, it's useless as is. Its existence only creates more confusion the way it stands now and is subject for complete deletion. [mr.anon]

Available Commands


This command is the main brunt of setting all feature parameters.

                 /--/-COLUMNS, ROWS to split picture into
                 |  |
                 |  |  MEASURE MODE (Y,U,V R,G,B) - U=0, Y=1, V=2, R=3, G=4, B=5
                 |  |  |
                 |  |  |  TIMEOUT
                 |  |  |  |
                 |  |  |  |  COMPARISON INTERVAL (msec)
                 |  |  |  |  |
                 |  |  |  |  |  THRESHOLD ( difference in cell to trigger detection)
                 |  |  |  |  |  |
                 |  |  |  |  |  |  DRAW GRID (0-no, 1-yes)
                 |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  RETURN VARIABLE number of cells with motion detected
                 |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |           OPTIONAL PARAMETERS:
                 |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  REGION (masking) mode: 0-no regions, 1-include,
                 |  |  |  |  |  |  |  |  |      2-exclude
                 |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  REGION FIRST COLUMN
                 |  |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  |  REGION FIRST ROW
                 |  |  |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  |  |  REGION LAST COLUM
                 |  |  |  |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  |  |  |  REGION LAST ROW
                 |  |  |  |  |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  |  |  |  |  PARAMETERS: 1-make immediate shoot,
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |   2-log debug information into file (* see note below!),
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |   4-dump liveview image from RAM to a file,
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |   8-on immediate shoot, don't release shutter.
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |   OR-ed values are accepted, e.g. use 9 for
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |   immediate shoot & don't release shutter
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  PIXELS STEP - Speed vs. Accuracy
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |    adjustments (1-use every pixel,
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |    2-use every second pixel, etc)
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  MILLISECONDS DELAY to begin
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |   triggering - can be useful
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |   for calibration with DRAW-
                 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |   GRID option.
md_detect_motion a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p

The minumum number of variables that must be set with this command are:

md_detect_motion a, b, c, d, e, f, g, h
Timeout: [mx3]it is time in milliseconds for which md_detect_motion will block execution of next ubasic commands if during this period no motion detected. this parameter is useful if you want to execute periodically some other ubasic commands together with MD.

i.e. MD routine waits for changes for 1 second. if no motion detected script can continue to execute some other code and then if required can resume motion detection by calling again md_detect_motion. so timeout is just time for which md routine will wait for changes. Practically, this TIMEOUT value (parameter d) shall be greater than the MILLISECONDS DELAY (parameter p), or else you will always get RETURN VARIABLE (parameter h)=0. (feel free to change this text to be better English)[/mx3]

Comparison Interval: The time delay in milliseconds in which to check for a change in a cell's values. If you need to filter out small changes made frequently by faster moving objects (leaves in the wind, or flying insects, for example) you would increase this value so that timed samples are further apart. Very useful when trying to detect changes in very slow moving subjects, i.e. snails, slime-molds, a slow-moving criminal trying to avoid motion detection devices :-), etc.
h - RETURNED VARIABLE: this variable must be used for decision whether you want to make shoot. it contains count of cells where change is more than specified threshold value.

example: if h>0 then shoot

n=2 (debug mode): Since build #684 (Jan 18th 2009), this debug feature has been removed to save RAM. To use it, a custom CHDK version must now be built (OPT_MD_DEBUG=1 in will enable motion detector debug).
(insert more information on variable parameter functions and uses as they become known or more familiar)


[mx3]it is optional procedure for those people who want to know where on scene actually detection happened. this procedure is designed for scene change advanced analysis. I'm not sure many people will need to use it. most people will need to use "h" variable from above sample to trigger shoot. (feel free to rephrase)[/mx3]

Usage: md_get_cell_diff (column), (row), x

Where x will be difference of 0 to 255 between the last and present change in that cell. Triggering a script to shoot on this value may be done by detecting no change, or how much sensitivity you would like to detect in that cell.

If you would like to have the camera shoot an image when all motion stops, use:
if x=0 then "shoot"
To shoot an image when any motion is detected at all use:
if x>0 then "shoot"

Interesting use of MD
The following was copied from a post where MX3 mentions a feature of md_get_cell_diff that was never documented before.
nobody tried to use MD to get overall luminosity to automatically
adjust shutter speed override?

MD setup:
set delay interval to 2-3 secs
threshold=255 (so it will not trigger ) 

md_get_cell_diff 1, 1, overall_luminocity

shutter_override_time = some_formulae ( overall_luminocity )

I don't have camera nearby to test it.

I have thought about timelapse movie script which would automatically override shutter speed at night. I'm planning to make 2 days timelapse
movie ( it seems 8gb SD card and power adapter will help also :-) )

NOTE: when MD stops working on timeout, cells containg absolute values instead of difference.
The most important info contained in that final "NOTE:".

Referring to the 'md_detect_motion' command-parameters in the WIKI article, 'a' and 'b' define the number of rows and columns to split the screen into. (If values less than zero are entered or if total number of cells is greater than 1024, it defaults to 3 x 3.)

Parameter 'g' determines if the grid showing the detected cells is displayed.

Parameters 'j,k,l,m' define a sub-area of the screen where motion-detection is restricted-to or excluded-from.

Parameter 'i' determines if the region is inclusion/exclusion or do not use regions.

You may detect motion based on changes of luminance (Y), blue – luminance (U), red – luminance (V) or individual R, G or B values.

Parameter 'c' sets that mode.

( For an example of an image split into it's YUV components, see this WIKI article. )

For non-specialized use, luminance (c = 1) will be used.

You then need to set a threshold-value (in parameter 'f') for the desired mode that will not result in triggering in 'normal' operation.

The motion-detection event may be triggered by quick or slow changes in the screen image, set a suitable value with parameter 'e'.

The greatest accuracy of movement-detection results when every pixel is sampled but a faster response (suitable for some applications) may be obtained with a larger pixel-step.

Set an appropriate value in parameter 'o'.

Set a maximum-time for a motion-detection event to occur with parameter 'd' so that after that time the script-command terminates.

Motion-detection Parameters :

columns, // input parameter. number of columns to split screen into

rows, // input parameter. number of rows to split screen into

pixel_measure_mode, // input parameter. // 1 - for Y, // 2 for U, // 3 for V, // 4 for gray, // 5 for R, - // 6 for G, // 7 for B

detection_timeout, // input parameter. number of milliseconds to abort detection. detected_cells_count will be 0 for timeout condition

measure_interval, // input parameter. number of milliseconds between comparison of two pictures

threshold, // input parameter. difference value for which procedure will trigger detection of changes

draw_grid, // boolean input parameter. // true(1) to draw grid(detected sectors/cells). // false(0) - to not display grid/detected sectors

detected_cells_count, // output parameter. count of cells where pixel values differs enough to trigger motion detection // clipping. allows to exclude some region from motion detection triggering // or use only selected area to make motion detection // I'm not sure that following parameters are required but using them anyway

clipping_region_mode, // input parameter. // 0 no clipping regions // 1 - for excluding selected region from motion detection // 2 - use this only region to make motion detection

clipping_region_column1, // input parameter.

clipping_region_row1, // input parameter. // this is top-left corner of clipping region

clipping_region_column2, // input parameter.

clipping_region_row2, // input parameter. // this is right bottom corner of clipping region)

function md_get_cell_diff ( col [in], // column of the cell we are requesting row [in], // row of the cell we are requesting val [out] // value of difference between measurements/comparisons)

reserved parameters clipping regions, pixel_measure_mode draw_grid

Camera Operation Commands

These commands are designed to allow your script to control your camera much like you would manually. Nearly anything you can do by pressing buttons on your camera with your own fingers, you can also do automatically with these script commands. The complexity and time-line of your script is only limited by your imagination and trying to keep your script under the 8K character (8192 byte) limit. (See "starting out" section above for script length limit; this might not be accurate any more)

Camera commands can be written in 3 flavors / command-methods:

  • click "button-name"
Presses the button momentarily, used for one time, instantaneous commands. This will be the most often used method of issuing a camera command.
  • press "button-name"
Presses and HOLDS the required camera button, it remains pressed until the same button-name is given the release command. Some camera commands can only be accessed when a button is held down during use.
Example: In Manual Focus in the S-series cameras the MF button needs to be held down while the focus commands are being issued. Or when shooting in high-speed burst mode, then the shutter button must be held down during its needed duration with the press "shoot_full" command.
  • release "button-name"
Ends the press "button-name" command. If using a press "button-name" command be sure to end it with the release "SAME-button-name command at the appropriate sequence in your script to reset things back to normal.

All camera command buttons that you can press manually you may use in your scripts using this syntax. The only exception is the often-used shoot command. shoot is used by itself without the leading click, press, and release command methods.

All button-pressing commands (except shoot) should be written in the following syntax:

command-method "button-name"

Where command-method may be click, press, or release, and the button-name must be enclosed in double-quotes.

For example, a simple script using all 3 command-methods which makes AELock and AFLock on A-series cameras:

sleep 2000 
press "shoot_half" 
sleep 1000 
click "erase" 
click "down" 
release "shoot_half"


Records an image.
This command is similar to the click "shoot_full" command (see below), but it waits for the camera to perform some normally automatic actions, such as auto-focusing, charging the flash, etc. For example: if in AUTO, P, Tv, Av, or any SCN modes, using the "shoot" command causes the camera to check focus and exposure for each shot. When "shoot" is used in intervalometer scripts this far surpasses the camera's own built-in intervalometer in that the camera only sets exposure and focus once for the initial exposure, as if it was only using the "click 'shoot_full'" command. This "shoot" command in an intervalometer script allows it to compensate for all the things that can change over the course of many minutes and hours. For more precise manual control of the camera in scripts, see the click "shoot_half", click "shoot_full", when used in conjunction with the get_tv, set_tv, set_tv_rel, get_av, set_av, set_av_rel commands below.

click/press/release "up", "down", "left", "right"

Actuates the respective directional button of your "Omni-Selector" (navigational buttons).

click/press/release "set"

Actuates the set button.
Note: press and release would not normally be used with this button, but without knowing each and every camera model's functions and the creative ways some might use scripts, these two command-methods are also mentioned.
On the SX10IS, holding down SET causes a clock to fill the display. The clock appears after holding the button down for ~2 seconds and disappears about 5 seconds after releasing the button.

click/press/release "shoot_half"

Actuates the shutter-release in the half-press position. This is often used to lock focus, exposure, or other camera settings.
(Note: In dim light it can sometimes take up to 2+ seconds for a camera to hunt for focus. If your script is using this command to set auto-focus, and is designed for or intended to also be used in low-light conditions, it would be good to follow a press "shoot_half" command with a sleep x command, where x can have a value from 1500 to 2500.)

click/press/release "shoot_full"

Actuates the shutter-release button completely, regardless if the camera has finished charging the flash or other normally automatic camera operations.

click/press/release "shoot_full_only"

Actuates only the shutter-release button "full press" internal switch. This is mostly useful where a click "shoot half" has been previously used and you wish to hold the focus and exposure locked. Doing a release "shoot_full_only" will then simulate only letting the shutter button up to the half-press position (whereas a release "shoot_full" simulates letting the shutter button return fully to the off position). (for more info, see this forum thread )

click/press/release "zoom_in", "zoom_out"

Initiates your camera's zoom control one zoom-step at a time. (It is uncertain at this time (I didn't test it), how this will act using the press and release commands.) The A-Series cameras have 9 or 15 zoom steps (0 to 8/14), and the S-series cameras have 129 zoom steps (0 to 128). This command may require an extra sleep command after each zoom step. When using click the S-series cameras implement this command very slowly. Here's an example of how it may be used in a loop:
for s=2 to a
    for n=1 to b
        print "Zooming-in ", n; "..."
        click "zoom_in"
        sleep 600
    next n

    print "Shoot", s, "of", a
next s
Note the 0.6 second sleep command after each zoom_in step.

click/press/release "menu"

Actuates the menu button.
This is used to alter some of the cameras settings that can only be set through the record menus, to set up the camera before a script-session, or during.
Note: press and release would not normally be used with this button, but without knowing each and every camera model's functions and the creative ways some might use scripts, these two command-methods are also mentioned.
  click "menu"
  sleep 400
  click "down"
  sleep 400
  click "down"
  sleep 400
  click "down"
  sleep 400 
  click "right"
  sleep 400
  click "menu"
  sleep 400
This :slowsync" sub-routine will initialize the camera's flash setting into slow-sync mode. Note also the sleep commands, giving your camera time to respond to the new settings between each directional button-press. Button-press delay times may be camera specific. (Meaning it might be a good idea to set up a user-defined variable for these in some scripts to save on script-size and make the script more adaptable to more makes and models of cameras. A note could be made in the accompanying script's documentation on what button-press delays are needed per make and model of camera.)

click/press/release "display"

Actuates the camera's display button.
Note: press and release would not normally be used with this button, but without knowing each and every camera model's functions and the creative ways some might use scripts, these two command-methods are also mentioned.

click/press/release "print"

Actuates the camera's print button. (Note: actuates the shortcut button for S-series cameras.)
Note: press and release would not normally be used with this button, but without knowing each and every camera model's functions and the creative ways some might use scripts, these two command-methods are also mentioned.

click/press/release "erase"

Actuates the camera's erase button. (Note: actuates the FUNC (function) button for S-series cameras.)
This will often be used to select some shooting parameters like exposure-compensation, movie frame-rates, white-balance settings, ... any of the options that can be reached by pressing this button on your camera. It is then used in conjunction with directional button-presses to choose the desired settings.
Note: press and release would not normally be used with this button, but without knowing each and every camera model's functions and the creative ways some might use scripts, these two command-methods are also mentioned.
@title EXP bracketing 
@param a Number of +/- steps 
@default a 2
@param b Step size (1/3EV)
@default b 3

if a<1 then let a=2
if b<1 then let b=3

sleep 1000

print "Preparing..."
click "erase"
for n=1 to a*b
    click "left"
next n

for s=1 to a*2
    print "Shoot", s, "of", a*2+1
    for n=1 to b
        click "right"
    next n
next s

print "Shoot", a*2+1, "of", a*2+1

print "Finalizing..."
for n=1 to a*b
    click "left"
next n
click "erase"

In this "Exposure Bracketing" script, if you follow the embedded button-presses, you'll see that your Exposure Compensation setting is being selected by using the click "erase" command. The click "right" and click "left" commands are moving the Exposure compensation settings to the right and left (more exposure and less exposure), just as you would if you were doing this manually from one shot to the next.

click/press/release "iso", "flash", "mf", "macro", "video", "timer" (S-series only)

Actuates the S-series specific buttons.

wait_click / is_key

wait_click timeout (waits for any button is clicked; timeout is optional)
is_key x "button-name" (if last clicked key was "button-name" the 1 will be placed to variable x; for timeout checking "no_key" is used as button name)

  is_key k "set"
    if k=1 then goto "continue"
goto "wait"

  wait_click 5000

  is_key k "left"
    if k=1 then gosub "k_left"
  is_key k "right"
    if k=1 then gosub "k_right"
  is_key k "set"
    if k=1 then goto "k_set"
  is_key k "no_key"
    if k=1 then goto "timeout"
goto "loop"

print "Timeout"
goto "end"




set_tv / get_tv

set_tv, get_tv, set_av, and get_tv are OBSOLETE. Newer versions of CHDK require
set_tv96 get_tv96
set_av96 get_av96
There are several commands for getting and setting the aperture and the speed. They only work in Manual mode; well you can change the settings in any mode, but they are effective in manual mode, probably also in Av and Tv modes). I put a test script for these commands in the "user written scripts"

The commands are

get_tv target    
set_tv_rel val     
set_tv val    
get_av target    
set_av_rel val    
set_av val
Target is the name of a variable (a, b, ..z), val is an expression.
An example of setting and printing the values.
set_av c    
set_tv b    
print "AV,TV set to",c,b    
sleep 1000    
click "shoot_half"    
sleep 100    
get_av n    
get_tv m    
print "AV,TV got",n,m    
You can change the settings relative to existing values:
rem increase light (1/3+1/3 steps)    
set_tv_rel 0-1    
set_av_rel 0-1    
This might make bracketing easier and faster

For A710is the Av and Tv settings provide the following actual values; roughly +/-1 setting means +/-1/3 EV change.
set_av	 set_tv     set_tv     set_tv      
 9 2.8  -12 15"     3 0.5"    19 1/80      
10 3.2  -11 13"     4 0.4"    20 1/100     
11 3.5  -10 10"     5 0.3"    21 1/125     
12 4.0              6 1/4     22 1/160     
13 4.5   -9 8"      7 1/5     23 1/200     
14 5.0   -8 6"      8 1/6     24 1/250     
15 5.6   -7 5"      9 1/8     25 1/320     
16 6.3   -6 4"     10 1/10    26 1/400     
17 7.1   -5 3.2"   11 1/13    27 1/500     
18 8.0   -4 2.5"   12 1/15    28 1/640     
         -3 2"     13 1/20    29 ???       
         -2 1.6"   14 1/25    30 1/800     
         -1 1.3"   15 1/30    31 1/1000    
          0 1"     16 1/40    32 1/1250    
          1 0.8"   17 1/50    33 1/1600    
          2 0.6"   18 1/60    34 1/2000

For A610 the Av and Tv settings provide the following actual values:
set_av	 set_tv     set_tv     set_tv      
 9 2.8  -13 15"     3 0.5"    19 1/80      
10 3.2  -12 13"     4 0.4"    20 1/100     
11 3.5  -11 10"     5 0.3"    21 1/125     
12 4.0  -10 ?       6 1/4     22 1/160     
13 4.5   -9 8"      7 1/5     23 1/200     
14 5.0   -8 6"      8 1/6     24 1/250     
15 5.6   -7 5"      9 1/8     25 1/320     
16 6.3   -6 4"     10 1/10    26 1/400     
17 7.1   -5 3.2"   11 1/13    27 1/500     
18 8.0   -4 2.5"   12 1/15    28 1/640     
         -3 2"     13 1/20    29 ???       
         -2 1.6"   14 1/25    30 1/800     
         -1 1.3"   15 1/30    31 1/1000    
          0 1"     16 1/40    32 1/1250    
          1 0.8"   17 1/50    33 1/1600    
          2 0.6"   18 1/60    34 1/2000    
                              35 1/2500
For the S2/S3 IS the Av and Tv settings provide the following actual values:
Aperture              Exposure    
Value  index    Value index     Value   index    
F/2.7  0        15"  -12        1/15    12    
F/3.2  10       13"  -11        1/20    13    
F/3.5  11       10"  -10        1/25    14    
F/4.0  12       8"   -9         1/30    15    
F/4.5  13       6"   -8         1/40    16    
F/5.0  14       5"   -7         1/50    17    
F/5.6  15       4"   -6         1/60    18    
F/6.3  16       3"2  -5         1/80    19    
F/7.1  17       2"5  -4         1/100   20    
F/8.0  18       2"   -3         1/125   21    
                1"6  -2         1/160   22    
                1"3  -1         1/200   23    
                1""   0         1/250   24    
                0"8   1         1/320   25    
                0"6   2         1/400   26    
                0"5   3         1/500   27    
                0"4   4         1/640   28    
                0"3   5         1/800   30    
                1/4   6         1/1000  31    
                1/5   7         1/1250  32    
                1/6   8         1/1600  33    
                1/8   9         1/2000  34    
                1/10  10        1/2500  35    
                1/13  11        1/3200  0
For Tv, 2 values are equal, 1" and 1/3200 with 0.

CHDK Build 119 Remapped Values (* = change)

S3-IS (Should be the same on all camera models now? If so we can remove the previous tables. Please confirm on other models.)

     Aperture              Exposure
   Value  index    Value index     Value   index
 * F/2.7  9      * 15"  -12        1/15    12
   F/3.2  10     * 13"  -11        1/20    13
   F/3.5  11     * 10"  -10        1/25    14
   F/4.0  12       8"   -9         1/30    15
   F/4.5  13       6"   -8         1/40    16
   F/5.0  14       5"   -7         1/50    17
   F/5.6  15       4"   -6         1/60    18
   F/6.3  16       3"2  -5         1/80    19
   F/7.1  17       2"5  -4         1/100   20
   F/8.0  18       2"   -3         1/125   21
                   1"6  -2         1/160   22
                   1"3  -1         1/200   23
                   1""   0         1/250   24
                   0"8   1         1/320   25
                   0"6   2         1/400   26
                   0"5   3         1/500   27
                   0"4   4         1/640   28
                   0"3   5       * 1/800   29
                   1/4   6       * 1/1000  30
                   1/5   7       * 1/1250  31
                   1/6   8       * 1/1600  32
                   1/8   9       * 1/2000  33
                   1/10  10      * 1/2500  34
                   1/13  11      * 1/3200  35

Usage Notes

When using the set_tv, set_tv_rel, or set_av, set_av_rel commands it was found that it may not be effective if inserted into a sequence of commands that used the press and in some instances the click "button" commands. If when testing your script that you find these commands will not alter the shutter-speed or aperture, try moving them to a position just before any press "shoot_half/full" or click "timer" (unique s-series) commands. For an example see the "Lightning Photography" scripts on where the set_tv command had to be placed before it would work. It was tried in all other locations before the actual shooting was to begin, setting the shutter-speed in other locations in the script wouldn't work otherwise.

There also seemed to be no problem setting a set_tv 0 value on S-series cameras with 0 being 1 second or 1/3200 second, it always defaulted to a 1 second shutter-speed. Since the 1/3200 speed is only available with an f/8.0 aperture setting, it might take a special way to trigger the 1/3200 shutter speed using a set_tv 0. Perhaps it can be done with a set_av 18, set_tv 35, set_tv_rel 1 sequence. Obsolete info for CHDK Build 119 or later.

set_zoom / set_zoom_rel / get_zoom / set_zoom_speed

set_zoom x (where x is 0 to 8, 14, or 129, see Range)
set_zoom_rel x (x is +/- relative change)
x = get_zoom (zoom-step value placed in variable x)
set_zoom_speed x (where x can be from 5-100 range. Will do nothing for A-series)
(5 is 5% of high-speed, 100 is 100% of high-speed)
A-series: x = 0 to 8 or 14 (9 or 15 steps)
S-series: x = 0 to 128 (129 steps)

Note 1: Camera does not refocus automatically after the end of zooming. Use a click or press/release "shoot_half" command to implement a refocusing if needed.

Note 2: It was found that if using the slowest speed (5), that an S3 IS might shut down after it has waited too long for the zoom to traverse the whole range of 129 steps, a speed of 10 did not exhibit this behavior on an S3 IS. 5 is so slow though, that I doubt it would rarely be needed, except in movie-shooting scripts, and then the range could be limited to prevent camera shut-down.

Note 3: CAUTION! (found on S3 IS) If set_zoom_speed is not written into the script when set_zoom x is used, the camera will refocus some of your optics to make it where the camera is unable to focus on anything in any mode. The camera (when zooming without a set-zoom speed) appears to move an internal lens element that puts the lens into a Super-Macro mode where it focuses on internal lens elements at widest-angle. If this command is left out of a script using the set_zoom x command, you will have to shut down your camera and restart it to reset the zoom-lens' optics back to defaults. However, an interesting thing is found -- when running the "Zoom-Shoot" script by rem-ing out the set_zoom_speed command (removing it from being implemented), after the camera resets its zoom, the lens is now in a ZOOMED tele-macro SUPER-MACRO MODE! Giving you close-up focusing ability at fullest zoom! (as if you had placed a +4 or so close-up lens on your camera) Far surpassing the capabilities that Canon designed. Perhaps this "bug" could be put to great use? Or it might damage your focusing and zooming mechanisms. USE WITH CAUTION. Because you can hear the camera strain up against some internal lens-adjustment stops when it's trying to reset the zoom. And the only way to "un-do" this (really nice!) tele-super-macro mode is by turning the camera off and on again.

(Leaving this small chart here for reference, but is no longer applicable to the new set_zoom commands.)

S-Series Zoom Speed: 36mm-432mm or 432mm-36mm
slow = 6 seconds (available in single-shot & movie mode)
medium = 4 seconds (available in movie mode)
high-speed = 1 second (available in single-shot mode)

set_focus / get_focus

uBasic Syntax:
set_focus x (where x is the distance in mm)
sleep 500+? delay required after call to set_focus and before shoot/shoot_half (see below)
shoot or shoot_half required after call to set_focus (see below)
x = get_focus (the current focus distance in mm is placed in variable x)
get_focus may also be used directly in an expression where its numerical value might fit: set_focus ((3 * get_focus) / 2)
would set a new focus distance 1.5X farther than the current distance.
LUA Syntax:
If you are having problems using set_focus, try putting your camera into P mode (with no chdk loaded: press camera/movie button, click right to highlight P, press set).
Note that most of the set_XXX commands happen when they are supposed to happen during the camera shooting process. So they should be called before shoot or shoot_half is called, and likely will not read back what you set them to until after shoot or shoot_half has been activated. If no set_XXX has been called prior to shoot/shoot_half, the camera will default to determining the values automatically.
Note that set_focus (on all cameras?) requires the execution of "shoot" before it takes effect:
@title focusTest1 script
print "Focus Test1!"
for f=95 to 100
  set_focus f
  sleep 500
  rem need shoot for focus to take effect!
  print "Set to=",f," Actual =",g
next f
If you comment out the "shoot" above, you will see that the focus will not change.
Use of press/release "shoot_half" also works (focus is set correctly after the press and is retained after the release as well). And note also that the delay "sleep 500" after set_focus is required. If you remove the "sleep 500" below it will fail (Set!=B4, Set!=Aft).
@title focusTest2 script
print "Focus Test2!"
for f=95 to 100
  set_focus f
  sleep 500
  press "shoot_half"
  sleep 1000
  release "shoot_half"
  print "Set=",f," B4=",b," Aft=",g
next f

Furthermore, the delay required after set_focus depends upon the distance the focus motor has to travel. So a step size of 1 between focus steps might require a sleep 500, while a step size of 10 might require a sleep 1500. Also, if in your script you set_tv, set_sv, set_av, this may cause your camera to adjust focus itself in which case the focus motor travel may not be from your last focus position but instead from where the camera auto focus left it (so may require a larger delay). If in doubt, use a sleep 3000 until everything is working.
When larger focus step changes are made, the end result reported by get_focus may be +/- 1 focus step from the set_focus value. So use caution if you loop waiting for get_focus to match.
More expensive Canon cameras with a manual focus mode may need to be put into manual focus mode (by issuing the sequence of click "ButtonName" commands for your camera) for set_focus to work. Cheaper point-and-shoots do not have manual focus mode and do not require this extra step. If your camera is missing the CHDK SD (subject distance) override menu, set_focus may not work for you.

set_iso / get_iso

To perform the equivalent action, newer scripts may wish to use set_sv96 and get_sv96 (see below) which use the APEX standard values.
set_iso x (where x is one of the following values: 0 - AutoISO; 1,2,3,4,5 - 50(80),100,200,400,800; -1 - HiISO (where applicable))
x = get_iso (the ISO value placed in variable x)


LED lamp conControl


set_led a b c
  • Note: this command may not work on all cameras !

I tried with A560 and it worked, but there is no led 10 (and not 6). And I think these work with any A500-series camera.

Parameter a is the LED-lamp as follows:

Value of "a"        LED Lamp
 4            GREEN (by power switch on S3 and A560)
 5            YELLOW (by power switch on S3 and under green led on A560 )
 6            (not used)
 7            ORANGE (red LED on back of S3 and same place than green on A560)
 8            BLUE
 9            Focus Assist / Auto-Focus Lamp / AF Lamp (bright green on S3 and bright orange on A560)
10            Timer / Tally Lamp (bright orange lamp in front on S3)

Parameter b

0 LED is off 1 LED is on

Parameter c (optional)

brightness 0 - 200, (Fingalo says, "Seems to work only on the blue LED.")

Leds work on A560, but this don't work any led on A560


rem Turn on AF_Lamp, Focus Assist Lamp
set_led 9 1

rem Turn on Blue LED with reduced brightness
set_led 8 1 35

IMPORTANT NOTE: When using any LED lamp controls, remember to reset them to their original condition as they were before executing your script. Failure to do so may result in your power-indicator not alerting you that your camera still powered on. Or other important camera functions involving the LED lamps may not light at their proper times.

Note 2: When testing the Blue LED brightness by putting it in a for x=0 to 200 loop to ramp the value all the way up in 1 value increments, then and back down again, it doesn't appear to behave linearly. The LED ramps up, then turns off, briefly flashes, ramps up again, flashes, then ramps down and flashes (or something similar to that). I suspect it might be working from 0 to 127 using binary bit values. But I've not tested it for this.


Read the battery voltage, momentary value, varies a bit.


a = get_vbatt

Value is returned in mV, millivolts, 1/1000th of a volt.

get_vbatt acts as its own variable, This allows you to even use it within strings, i.e. if (get_vbatt <= 4300) then print "DEAD BATTERY!"


enable / disable RAW recording


set_raw a


a = 0 then RAW recording is OFF
a = 1 then RAW recording is ON


Returns enable / disable state of RAW recording. 1 = RAW enabled; 0 = RAW disabled

x = get_raw

As with most (all?) get_xxxx variables, the function can also be used directly in an equation or as a Boolean value:

if get_raw then [do stuff]

will execute [do stuff] if RAW is enabled.


Set "Dark Frame Subtraction" state (ON|OFF|AUTO); in earlier builds this was called "noise reduction" (nr).

Determines whether the camera will do a dark frame subtraction after taking a shot. Auto means the camera decides, OFF means no, ON means yes. Dark frame acquistion and subtraction typically occures for images with an exposure time of 2/3 of a second or longer. It does consume time (it's equivalent to taking another image at the same exposure time).

Note: although this command refers to "raw", it actually applies regardless of whether you are in RAW mode or not. AUTO is the state the camera normally is in. CHDK allows you to change this to the ON or OFF states, and this uBasic command allows you to change it in a script.


set_raw_nr a


the variable a determines the state: 0=Auto 1=OFF, 2=ON


This function returns the time, in milliseconds, since the camera was turned on. Note that this function format is a bit different from the standard CHDK uBasic function format.


t = get_tick_count
get_tick_count acts as its own variable, This allows you to even use it within calculations without first assigning it to another variable.


This function returns the number of seconds since midnight. Note that this function format is a bit different from the standard CHDK uBasic function format.


t = get_day_seconds
get_day_seconds acts as its own variable, This allows you to even use it within calculations without first assigning it to another variable.

For a simple example using this function to wait until a specific time of day before continuing, see get_day_seconds_example.

set_prop / get_prop

---> this section needs to be updated to reflect the actual state !

Read / Set PropertyCase Values

This is a powerful pair of commands. These are used to read and set "property-case" values in the firmware of your camera. They can be used for: detecting and setting the flash mode, mode-dial position, the internal self-timer delay, video frame rates, and more.

A new page has been created to describe the use of some of the more useful property case values. See this link The Property Case Use page

The presently known property-case values were originally taken from a list posed at a Russian authored List of known Property Cases. A more up to date list can be found here: this page of Property Case IDs [There now is a Discussion page section for user contributions to determining the values and uses of the property cases. It also has a link to script for exploring these items. You can find it here: Property case exploration.]



set_prop propid value
get_prop propid value

Where propid may be any of the following:

Prop_ID   Description

 0        Shooting mode dial position
 1        Photo effect
 5        White balance
 6        Drive mode (S3 values: 0=single, 1=continuous, 2=timer)
 8        Hi-speed continuous mode (S3: 1=OFF, 0=ON
 9        Metering mode (S3 values: 0=eval 1=spot 2=center)
11        Macro (S3 values: 0=normal, 1=macro, 2=super mac)
12        Manual Focus (S3 values: 1=manual, 0=auto)
14        Delay of selftimer (appears to be time in milliseconds)
16        Flash mode (s3: 2=flash closed, otherwise 0=auto, 1=ON)
18        Red eye mode (S3: 0=OFF, 1=ON)
19        Flash slow sync (S3: 0=OFF, 1=ON)
20        Flash Sync Curtain (S3: 0= first, 1 = second)
21        ISO value (S3: 0=auto, 1=ISO-HI, or actual ISO: 80,100,200,400,800)
23        Image quality (S3 values: 0,1,2 from best to worst)
24        Image resolution (S3 values: 0,1,2,4,8 for L,M1,M2,S,W)
25,26     EV correction (positive or negative, 96 units per stop)
28        Flash correction (same units as 25,26)
32        Exp bracket range (Same units as 25/26: e.g. 96 = +/- 1 stop range)
34        Focus bracket range 2=Smallest, 1=Medium, 0=largest
36        Bracket mode: 0=NONE, 1 = exposure, 2 = focus
37        Orientation sensor
39        Chosen Av (by user)
40        Chosen Tv (by user)
65        Focus distance
67        Focus ok: 1=Yes, 0=NO
68        Coming Av
69        Coming Tv
74        AE lock: 1=ON, 0=OFF
126       Video FPS (15, 30 or 60.  don't change here!)
127,128   Video resolution (S3: 2,1 for 640x480; 1,0 for 320x240)
177       intervalometer: #of shots (0 if not activated)
205       0 '1' during shooting process
206       "MyColors?" mode (See link below)
2,3,4,207,208,209,210 contain individual parameters for the "Custom" MyColors
218       Custom timer continuous: # of shots to be taken
219       Self Timer setting: 0=2 sec, 1=10 sec, 2=custom continuous

And value may be any that is appropriate for that particular propid.

Additional information (hopefully growing) about what values might work for some of these properties can be found at the following link: Property case exploration page. This link also has a more complete description of the MyColors settings (contrast, saturation, sharpness, individual color intensities, etc)

Example script for setting and viewing Prop_IDs.

@title popcase
@param a propid
@default a 0
@param b value
@default b 0
  is_key k "left" 
    if k=1 then set_prop a b 
  is_key k "set" 
  if k=1 then goto "lend" 
  get_prop a b
  print a,b
goto "loop" 

Enhanced & new commands

The Allbest build is a major rewrite of CHDK, in many ways. It also includes many new uBASIC commands. Below is a partial list of the complete list of available commands, those which are unique to the Allbest build. These have not been documented in total yet, and more uBASIC commands are being added frequently. (Please see the CHDK forum for discussions of any works in progress.)

NOTE: Syntax usage in most cases is command_name x, where x either sets or returns the value in that command. Unless stated otherwise, assume this usage syntax. Otherwise they may be acting as their own variable, and may be used :as-is in a command string. Example: get_vbatt is its own variable. It can either be assigned to another variable with x=get_vbatt, or used on its own as in print get_vbatt. The different types of uBASIC command syntax will be clarified as needed or as discovered. (Developers don't document things very well. We, as end-users, sometimes have to find these things by trial-and-error, or be perceived as a major nuisance by hounding them for any clues into what they did. :) I use both methods. :) )


For the functions listed below CHDK uses APEX values to set and calculate exposure.


This function returns the current aperature setting in APEX96 units.


This function returns the current brightness value in APEX96 units.


Get the depth of sharpness in mm, as calculated from your current focal length (zoom) and aperture (Av). Use it as a number in an equation: n = get_dof

You can do arithmetic directly with the get_xxxx variables. For example, to increase the focus value you already have stored in f by the depth of field, you can write

n = get_dof

f = f + n

Or you can combine the steps:

f = f + get_dof


Get the maximum distance of acceptable sharpness in mm. The difference between far limit and near limit is your depth of field. CHDK calculates the values from the cameras current focal length (zoom), aperture (Av), and focus distance.

n = get_far_limit

is the most basic use, but it can be combined into more complex arithmetic expressions.


Get hyperfocal distance

n = get_hyp_dist

Depth of field is that range of distances that are acceptably focused, given the lens's focal length (zoom), aperture (Av), and focus distance. Hyperfocal distance is the closest distance the lens can focus and still be sharp to infinity. When the subject distance (focus) is set to the hyperfocal distance, get_far_limit will equal infinity, and get_near_limit will be 0.5 * the focus distance.


get "marketing" ISO (See the Allbest's Firmware Usage page on ISO values for what is meant by a "Market Value".)


obtain ISO mode (the former get_iso)

Eg. the A620 list
0-> Auto "
50-> 50 "
100-> 100,
200-> 200,
400-> 400,


get real "value" ISO


Get the closest distance that is within the range of acceptable sharpness.

n = get_near_limit

Near limit and far limit combine to define the camera's depth of field (see get_dof), the range of distances that is acceptably sharp. CHDK calculates the values based on the current settings for focal length (zoom), aperture (Av), and focus distance.


Returns the Speed Value (ISO, image sensor sensitivity) that the camera is set to in APEX96 units. Use in conjunction with set_sv96.
uBasic Syntax: get_sv96 x
LUA Syntax: x=get_sv96()
Note that typically get_XXX is called at the beginning of a script after a shoot_half to grab what the camera would automatically set the value to. And then get_XXX is called after a set_xxx and shoot combination later in the script along with a print or log of the value to verify that the value read back matches what was set.
If you are unfamiliar with APEX refer to the wikipedia article: The values used by Canon and CHDK are the APEX value multiplied by 96 (thus the 96 in the name). The simplified explanation for APEX is that the amount of light hitting the film/sensor is dependent on the aperture value and time value (shutter speed) and should be matched to the brightness value of the subject being photographed and the speed value of the film/sensor (ISO value).


Returns the Time Value (shutter speed) of the camera in APEX96 units. Use in conjunction with set_tv96 described below.
uBasic Syntax: get_tv96 x
LUA Syntax: x=get_tv96()
Note that typically get_XXX is called at the beginning of a script after a shoot_half to grab what the camera would automatically set the value to. And then get_XXX is called after a set_xxx and shoot combination later in the script along with a print or log of the value to verify that the value read back matches what was set.
If you are unfamiliar with APEX refer to the wikipedia article: The values used by Canon and CHDK are the APEX value multiplied by 96 (thus the 96 in the name). The simplified explanation for APEX is that the amount of light hitting the film/sensor is dependent on the aperture value and time value (shutter speed) and should be matched to the brightness value of the subject being photographed and the speed value of the film/sensor (ISO value).


the former get_av. Get custom installation av (in the manual modes) for ID in CHDK

Eg. the A620 list
(9, 288, "2.8")
(10, 320, "3.2")
(11, 352, "3.5")
(12, 384, "4.0")
(13, 416, "4.5")
(14, 448, "5.0")
(15, 480, "5.6")
(16, 512, "6.3")
(17, 544, "7.1")
(18, 576, "8.0")
The first of values-in ID CHDK. The move to the next ID is, in fact, a shift in the 1/3 ev. The second value is a av * 96


returns custom av * 96


returns CHDK identifier for the established user manual modes tv.

Eg. the A620 list
(-4, -128, "2.5")
(-3, -96, "2")
(-2, -64, "1.6")
(-1, -32, "1.3")
(0, 0, "1")
(1, 32, "0.8")
(2, 64, "0.6")
(3, 96, "0.5")
(4, 128, "0.4")
Important: earlier scripts just use the "get_tv" and "get_av" commands, these must be changed to this newer "get_user_tv_id" and "get_user_av_id" commands to make them work properly if using Allbest builds.
This is part of possible values. Meaning load deflection on the id-the same as in the case of av


returns value installed in the user manual modes importance tv * 96


Directly set the aperture, without allowing Canon to round to the nearest 1/3 stop. Theoretically precise to 1/96 of a full f/-stop, though the mechanics of the camera is unlikely to match that precision. Works in any mode.

Unlike the recommended set_tv96_direct which simply changes a timer, since this moves the aperture motor, use caution when using this function. It may be safer to use set_av96 below (assuming it alters your value to a safe setting before applying - I don't know...)
Note that most lower cost Canon point-and-shoot cameras do not have a variable aperture and simply rely upon the shutter speed to determine the amount of exposure to the subject light that is allowed to reach the image sensor. See set_tv96_direct below.
set_av96_direct should allow you to use in-between values not in the table. Convert the desired aperture (f-stop) to and Av96 value with the formula:
Av96 = 192 * ln(f-stop) / ln(2)
(answer must be rounded to a whole number)
f-stop = 2 ^ (Av96 / 192)
CAUTION: The formulas above don't acknowledge any limits to the width or narrowness of your camera's aperture. Attempting to exceed the limits of your model may damage the aperture motor or mechanism.


see "set_user_av_by_id_rel (compatibility)


the installation av * 96 in accordance with acceptable Canon list for the camera. Works in any mode

Note that most lower cost Canon point-and-shoot cameras do not have a variable aperture and simply rely upon the shutter speed to determine the amount of exposure to the subject light that is allowed to reach the image sensor. See set_tv96_direct below.


see "set_user_av_by_id (compatibility)


the installation of a regime ISO.


Direct installation ISO. It works similar to the installation of the ISO interface CHDK


Used to set the Speed Value (ISO) with a APEX96 value. The Speed Value is the sensitivity of the camera's image sensor. Typically: higher sensitivity used for fast action shots at the expense of detail versus lower sensitivity used for slow/static shots with higher detail, but requiring longer exposure times.
uBasic Syntax: set_sv96 x
LUA Syntax: set_sv96(x)
Note that you can determine the APEX96 value for ISO XXX by first setting your camera to ISO XXX then running a script which calls get_sv96 and prints the result. To set your iso: when chdk is not loaded: press set, then up to the top line then right to select the iso value, then set again. (Not sure whether the APEX96 values versus ISO values match from camera to camera, so this method will always work.)
If you are unfamiliar with APEX refer to the wikipedia article: The values used by Canon and CHDK are the APEX value multiplied by 96 (thus the 96 in the name). The simplified explanation for APEX is that the amount of light hitting the film/sensor is dependent on the aperture value and time value (shutter speed) and should be matched to the brightness value of the subject being photographed and the speed value of the film/sensor (ISO value).
Note that most of the set_XXX commands happen when they are supposed to happen during the camera shooting process. So they should be called before shoot or shoot_half is called, and likely will not read back what you set them to until after shoot or shoot_half has been activated. If no set_XXX has been called prior to shoot/shoot_half, the camera will default to determining the values automatically.


This is the recommended method of setting Time Value (shutter speed) for new scripts. It uses a APEX96 value. Note that set_tv96 (no "direct" in the name) will attempt to round the setting passed to nearest camera standard shutter speed and can have unpredictable results (using get_tv96 you may read back values that differ from what you set). While set_tv96_direct will set the value you passed it without attempting to alter it. If you wish to stay within your camera's published shutter speeds (not required, but maybe you want to for other reasons) you can still use set_tv96_direct using the standard values. For standard values, refer to the table below (note that they are simply multiples of 32: N*32).
uBasic Syntax: set_tv96_direct x
LUA syntax: set_tv96_direct(x)
Note that most lower cost Canon point-and-shoot cameras do not have a variable aperture and simply rely upon the shutter speed set by this time value to determine the amount of subject light that is allowed to reach the image sensor. But don't be concerned; because of the increased sensitivity of digital image sensors (versus film), the results are still excellent after the cost reduction of removing aperture control. Note that these lower cost cameras use the Neutral Density Filter to compensate for the lack of aperture control (see You will likely want to disable this filter by issuing the command set_nd_filter(2) to give yourself complete control of exposure.
If your exposures still seem to contradict what you expect, try setting your camera to a fixed ISO setting (instead of auto iso). When CHDK is not loaded do: press SET to bring up the hidden menu most do not realize is there, scroll up to the top entry (usually) then right/left to choose iso speed. Alternatively, in your script, perform a get_sv96 at the beginning of your script after a shoot_half (which will grab the autoiso value the camera thinks you should use, or your fixed setting if not autoiso), then perform a set_sv96 (with this grabbed value) coupled with your set_tv96_direct before the actual shoot/shoot_half when taking your shots.
Just as with set_focus, you may need to add a delay (sleep 1500) after set_tv96_direct and before a subsequent set_focus or shoot/shoot_half. (Not sure why this is, but, seems to be required in my case.)
If you are unfamiliar with APEX refer to the wikipedia article: The values used by Canon and CHDK are the APEX value multiplied by 96 (thus the 96 in the name). The simplified explanation for APEX is that the amount of light hitting the film/sensor is dependent on the aperture value and time value (shutter speed) and should be matched to the brightness value of the subject being photographed and the speed value of the film/sensor (ISO value).
Note that most of the set_XXX commands happen when they are supposed to happen during the camera shooting process. So they should be called before shoot or shoot_half is called, and likely will not read back what you set them to until after shoot or shoot_half has been activated. If no set_XXX has been called prior to shoot/shoot_half, the camera will default to determining the values automatically.
Non-standard Shutter speed tv96_direct values can be calculated with this formula:
Tv96 = -96 * ln(shutter time) / ln(2)
Answer must be rounded to nearest whole-number value.
shutter time = 2 ^ (Tv96 / -96)
Table of standard shutter speeds and the corresponding tv96 value (where " is shorthand for second):
speed = tv96
64.0" = -576
50.8" = -544
40.3" = -512
32.0" = -480
25.4" = -448
20.0" = -416
16.0" = -384
12.7" = -352
10.0" = -320
8.0"  = -288
6.3"  = -256
5.0"  = -224
4.0"  = -192
3.2"  = -160
2.5"  = -128
2.0"  =  -96
1.6"  =  -64
1.3"  =  -32
1.0"  =    0
0.8"  =   32
0.6"  =   64
0.5"  =   96
0.4"  =  128
0.3"  =  160
1/4"  =  192
1/5"  =  224
1/6"  =  256
1/8"  =  288
1/10" =  320
1/13" =  352
1/15" =  384
1/20" =  416
1/25" =  448
1/30" =  480
1/40" =  512
1/50" =  544
1/60" =  576
1/80" =  608
1/100" = 640
1/125" = 672
1/160" = 704
1/200" = 736
1/250" = 768
1/320" = 800
1/400" = 832
1/500" = 864
1/640" = 896
1/800" = 928
1/1000" = 960
1/1250" = 992
1/1600" = 1024
1/2000" = 1056


see "set_user_tv_rel_by_id" (interoperability)


Not recommended as results can be unpredictable. See set_tv96_direct above.

direct tv installation * 96 from a list of valid values CANON (this value type N * 32. N for the A620 can have values from -12 to 32. works by installing excerpts from the CHDK interface


see "set_user_tv_by_id" (interoperability)


av installation on the current user on bias. The offset indicated in Id. The Id rationale was listed above.


Custom Installation av according to the Id in CHDK. The point above id-


custom installation av * 96 in the manual modes


custom installation on the current tv on bias. The offset indicated in Id. Id rationale was listed above


the installation of custom tv permissible, in accordance with Canon ID for CHDK


the installation of custom Tv * 96. Of the number of allowable and non C

Example Exposure Setting Script

If you are using this to set a shutter speed, set it to 138*ln(x), where x is the time in seconds.
Example of usage (set_shutter for Ixus) by Allbest
@title Shutter TEST
sleep 500
rem initiation
press "shoot_half"
release "shoot_half"
get_tv96 t
print "Tv set to",t
is_key k "set"
if k=1 then goto "k_set"
is_key k "down"
if k=1 then t=t-32
is_key k "up"
if k=1 then t=t+32
set_tv96_direct t
goto "set_shutter"


Simulates the movment of the jog dial one click clockwise.


Simulates the movment of the jog dial one click counterclockwise.


parameter checking autostart for scripts

Syntax: x=get_autostart (or used as it's own variable-string in calculations, see get_vbatt example)


Setting this option to autostart scripts

With these commands should be cautious. Specified Autorun leads to the script when you turn a camera on.


checking for USB connectivity. Works for series A and S-as a minimum.

Syntax x=get_usb_power


Simply powers-down the camera. Useful for Remote USB scripts where the USB signal may wake up the camera, execute some script function, and then shut down the camera again when done, to save on power for lengthy remote-shooting needs.
Example, if x=(some calculation) then shut_down, or just used as a line on its own at the end of your script.
Note : in Lua, you can also use post_levent_to_ui('PressPowerButton') which may prove to be more reliable as it will be treated by the camera firmware just like a real power button press



Returns values in KB. You can build scripts now which stop when specific disk limit exceeded. For easier calculation divide by 1024 to return value in MB.
Syntax: x=get_disk_size, x=get_free_disk_space
Example, to print the space left in megabytes, print get_free_disk_space/1024 (this, among some others, is one of those commands that acts as its own variable)



Syntax: x=get_jpg_count, x=get_raw_count (acts as its own variable which may be assigned to other variables)
Returns the calculated value of how many JPG or RAW shot space is left available on the SD card. (JPG value is approximated and taken from an average of file-sizes, using Canon's own algorithm, the same as shots remaining left in your EVF/LCD display.) Use this command to detect when not enough space is remaining for your required script task to either end the script or shut_down the camera.


Controls the ND (Neutral Density) filter


0 = OFF
1 = ND filter IN
2 = ND filter OUT

This ability replaces aperture override menu entry for most Ixus series cameras and also some of the cheaper Axx cameras.


Returns the condition of your NR (noise reduction setting).
Syntax: x=get_raw_nr

USB Remote Cable-Release Function

This amazing feature was found by a talented Ukrainian programmer known as Zosim. You may find his original source code and executable binaries for the A710 IS camera at CHDK binaries and source and photos to build simple cable-release switch. Fingalo and Microfunguy have both added this remarkable addition to their builds of CHDK.

Be SURE to also check out the Special Builds Features in the Firmware Usage page for two new Script Menu items on how you can use this feature to completely operate your camera by remote control only. From turning it on to executing your last loaded/used script.

Using nothing more than a 3-volt button-battery and a small switch, you may turn any USB extension cable into a remote shutter release by running a small script. Or by using this script method as a subroutine within your own much more complex scripts.

NOTE: This feature is only available to camera models A610, A620, A630, A640, A710, and S3 IS so far. It is unknown at this time if it is adaptable to the other cameras supported by CHDK. (Though, I get the feeling someone will eventually find a way.)
The above is no longer true. Most all the cameras are supported for the Remote USB feature, and most all of the different builds also include it now.
IMPORTANT: With this remote function in these builds the camera will not enter download mode when connecting your computer's USB cable while CHDK is loaded. For normal camera to computer download mode just disable CHDK by turning off write protect on the SD card. However, while CHDK is running a USB-Remote script you may use the USB connection of your computer to easily test that all is working properly. When connecting camera to computer the 5-volts on the computer's USB port will be detected and activate your script command(s).
The above is no longer true on more recent builds of CHDK. There are now two new functions available in the Scripting Menu to enable or disable remote sensing so that you may still download images from your camera while CHDK is still loaded and running as well as a setting to allow activating the last loaded script. See the "Special Build Usage" section for a little more info.


special remote camera button, used in is_key commmands with is_key x "remote"

Running this small script (or the loop embedded as a subroutine in more lengthy scripts) is all you will need:

@title Remote button
wait_click 1
is_key k "remote"
if k=1 then shoot
goto "loop"

Or, if using Fingalo's builds you may like his version with the simpler while/wend loop commands:

@title Remote button
while 1
  wait_click 1
  if is_key "remote" then shoot


There are many ways of using this "remote" key function, these are just two of the more simple (and faster) ways to implement it.

That's it! That's all you need! Well, one of those little scripts, the right CHDK build, and the cable-switch (this link is 404 - Soapytoo 22:50, July 14, 2010 - use instead) too. :-)

Between MX3's Motion-Detection options and this amazing USB cable-release method, there is no limit to the various ways you may control your camera by remote means. Any simple electronic circuit that can close a switch and feed a 3v to 5v DC signal to the USB port's proper contacts (observe proper polarity!) can now be used. There is also no limit to the length of wire that you may use, as long as you keep the final contact voltage at the camera-end between the 3vdc and 5vdc range. Use sound-sensitive circuits to record when sound-events happen. Use light or motion changing events to trigger shooting sessions. Use any CHDK intervalometer scripts or electronic intervalometer circuits to trigger shots. (There are thousands of simple circuits like these all over the internet.) Have your mouse or cat press a switch to record their vanity-quotient for a science-fair project! The sky (literally) is the limit to how many ways you may use these functions.

Have fun!

Debugging: uBasic

Understanding the Unk Alert, uBasic only

This tiny version of uBASIC includes some debugging help. When running a script with a bad command you might sometimes get a uBASIC:nn err statement printed in red in the top-left corner of your EVF or LCD display. This will alert you to why your coding didn't work, albeit in a very abbreviated format giving the line (nn) and error message.
Some exmaples of what you might see, and what they will mean:
uBASIC:24 Unk label Line 24 Unknown label 
uBASIC:32 Parse err Line 32 Parse error - syntax error in uBASIC command
See the following sections for IDE and debugging aids ideal for both novice uBASIC developers as well as the more experienced.

Some unexpected behaviour of uBASIC

These are my observations, which might be inaccurate.

do not "execute" labels

After release #68 this is not true, you can leave out the "goto "nega"" statement. Also the extra space after the label is not necessary any more.
if a<0 then goto "nega"
let a=5*6
goto "nega"      
rem If this line is left out and a>=0 then an error 
rem (unk statement or unk label) will be generated

Debugging Scripts on a PC or Mac

There are now two ways you can test your CHDK scripts without needing to load them into the camera every time, finding the error and then changing a line, loading it into the camera again and again. The first way is to use the ubasic_test program, a simple batch program which only runs under Windows. The second way is to use the UBDebug program which runs under Windows or Mac OSX.

Using UBDebug - an Integrated Development Environment for Scripts

There's now an interactive development environment for uBasic scripts. Written in java with native support5 for both Windows and Mac OSX it lets you load a script and step through it line by line, inspecting and setting variables. You can also set the values to be returned by functions (such as get_usb_power) and alter the value of properties. A simple breakpoint mechanism is available. Scripts can be edited and saved to disk. For details see here

Using the UBASIC_TEST.EXE Console

Download this small file (BEWARE - LINK TRIES TO INSTALL ADWARE ON YOUR COMPUTER!  SUGGEST FINDING THE FILE ELSEWHERE).  UnRAR (like UnZIP) it to your scripts working location on your hard-drive. You should have a file named ubasic_test.exe in your scripts-work folder now. You have to run this program from a Windows Command Prompt (the old time DOS window). Some people have a "Launch Command Prompt Here" on the right-click menu of Windows Explorer, so you can just right-click on the folder where your scripts and ubasic_test.exe file reside. (You can get this by installing "Open Command Window Here" Power Toy, available here.) Or you can go to Programs > Accessories > Command Prompt (where I have mine for some reason). And use the CD command to Change Directories until you get to where your scripts and ubasic_test.exe file reside. For example, if you start out in root directory C:\ and your scripts are on drive D: in a sub-folder called CHDK\Files\Scripts\, at the command prompt just type
cd D:\CHDK\Files\Scripts
and you'll be where you're supposed to be. (You might want to rename that little program to just test.exe to make it easier to type each time.)
To test one of your scripts in that folder, at the Command Prompt, just type "ubasic_test scriptname.bas" (without the quotes). Where "scriptname.bas" is the name of the script you want to test. It will use the default settings you have assigned to your variables. For testing you should change some of those values to make sure everything is working properly under new user-defined settings. (The reason I suggest you rename that ubasic_test.exe to just text.exe, is then all you have to type is "test scriptname.bas", saving you a few key-presses.)
The easiest way to run console programs is to use a file manager which has a command line. For example, Far Manager or Total Commander.
You can also test your scripts via drag&drop with a batch file. Here's how to do it:
Open a texteditor and put the following lines in there:
@ubasic_test.exe %1
Save this as "ubasic_test.bat" in the same folder where your ubasic_test.exe is. Now you can drag a script with your mouse onto this batch file and it will be executed. (This would also work without making a special batch file, but we need the "pause" command to read the output).

You may need to modify your BAT file to have the @ubasic_test.exe %1 line to include the full path to your ubasic_text.exe file, as well as enclosing the variable %1 in quotes, in case your script's filename includes any spaces. For example:
@H:\Tests\CHDK_Files\SCRIPTS\ubasic_test.exe "%1"
If you run into problems and this still doesn't work (using this drag & drop method):
  • 1) Make sure your ubasic_test.exe file and scripts are not in any path that contains spaces. (Example: you can't have it in a sub-folder path of "D:\CHDK Files\Script Tests\ubasic_test.exe" Change those spaces to _ (underscores) in your actual folder-names if need be.)
  • 2) Your BAT file association may have become corrupted. Here's a handy page of Windows® XP File Association Fixes Get the one for Batch Files. (Save them all, they may come in handy one day!)
(How did I find this out? I had all these problems going for me. :-) )

An alternative drag and drop method (WinXP):-

1) Rightclick on uBasic.exe and make a shortcut on desktop,
 2) Find/search for your script.
 3) drag your script to uBasic icon letgo and it runs!

You may have to adjust the 'Icon' properties to keep the result on-screen

The addition of a few extra print and rem statements will help debugging, also include values to replace the @defaults.


  1. 1.0 1.1 1.2

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