APM to CHDK Camera Link Tutorial

[Edit 12/31/2015: Note for Pixhawk users that Canon cameras require a 5V pulse to trigger so a voltage step-up from Pixhawk's 3.3V output is required. See compatible cable and link to more instructions here.]

ArduPilot Camera Tie-In Tutorial

This tutorial will show you how to get your CHDK-enabled camera connected to your ArduPilot Mega (APM) without buying any extra hardware or decoding PWM outputs. You might want to make this connection to take advantage of the camera trigger function based on distance covered, to ensure a certain overlap and to avoid excessively high overlap. This modification is not necessary, if you have a CHDK camera and want to keep it simple, you won’t gain much by switching to this method right away.

For this tutorial, I’ll use an SX260 HS but this should work equally well on any CHDK-supported Canon Powershot camera. You’ll need just the supplies below to make the cable. The SX260 uses a USB Mini-B connector. Most Powershot cameras come with a USB cable, you can just use that one to be safe.

APM CHDK Connection

If you don’t have a crimp tool to attach the servo connector, just take a spare servo wire and solder the wires together instead.

We’ll only be using the Mini-B side of this cable, so measure whatever length you need from that end depending on how your camera and autopilot mount in your airframe. I’ve measured out about 14″ and cut the cable completely through. Inside are four wires, we only need the red and black wire so cut away the green and white wires. Strip the ends of the red and black wires.


If you have the crimp tool, crimp and insert the wires into the first and third positions of a 3-position header. If you don’t have the crimp tool, solder these two wires to the ground and signal wires of a spare servo wire. Insert the ground wire into the side with an arrow so you can tell which wire is which later on.


Cover the connector with heatshrink. Be careful with the hot air near the connector as it can cause the locking plastic pieces in the receptacle to deform.

CHDK Cable

Now plug this cable into pin A9 on the side row of APM. The text doesn’t line up exactly so be sure to count rows. SPI takes two rows, then A11 and A10 are two more so there should be 4 rows of free pins, then our new connector.

APM Relay Pin A9

If you already have CHDK installed, just install the script file (right click, save link as) into the scripts directory on your SD card. If not, follow instructions for installing CHDK from the page corresponding to your camera atthe CHDK wiki. Load up CHDK and go into the menu then navigate to Miscellaneous Stuff -> Remote Parameters and make sure the Enable Remote setting is checked.


Now connect to your APM and open the Full Parameters List in the Config/Tuning tab. Set the parameters as following:

  • CAM_TRIGG_DIST: Depending on overlap required.. be sure to keep in mind the normal downwind speed of your plane as well as the maximum rate at which the camera can take pictures. For the SX260 and the E382 that’s once every 2.7 seconds and about 18m/s. I plan to operate below those condition in most cases but I do like to get as many pictures as possible, so I set my distance to 49 (meters).
  • RELAY_PIN: 13



All that’s left is to test it out. Load the E38_APM.bas script file like any normal CHDK script and start running it. If you can get a 3d fix inside, you can test it on your lab bench just using USB power. Just set the CAM_TRIGG_DIST to 1 or 2 meters and let your plane sit on the desk. Small movements between GPS readings will cause the distance value to count up slowly and it should trigger the shutter every few seconds.

If your camera lens closes and opens instead of taking a picture, make sure the CHDK remote enable setting saved properly. If nothing happens at all, take your APM outside and walk around to make sure you are getting some distance covered.

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  • T3

    @AndyC, try to reduce CAM_TRIGG_DIST to maybe 3, Enable Remote on your camera, and check that your scripts works properly. Then it should be no problem. Also be careful that you are really using A9 and not A10.

  • @Thorsten. Thanks for your help. Currently I've got CAM_TRIGG_DIST=1 and I'm trying to use the signal pin; my problem is that's not working. I'm interpreting the fact that the camera does trigger when I connect to the power pin as indicating my problem lies with the signal being sent to the A9 signal pin, due to the way I've set my parameters.

  • T3


    it is ground and signal not power and signal. Also check CAM_TRIGG_DIST.



  • Thanks for the great tutorial. Can anyone help me work out why my camera won't trigger from the A9 signal pin?

    I know my cable and CHDK are okay because the shutter triggers continuously if I connect the USB signal wire to the + power rail. I'm using APM 2.6, ArduCopter 3.1.5, Mission Planner 1.3.7, with CAM_DURATION=1, CAM_TRIGG_TYPE=1, and RELAY_PIN=13. Any suggestions very welcome.

  • The script also plays with exposure to maximize the settings you want (like shutter speed).. but realistically you can just use the Tv mode and get the same result 99% of the time.

  • Thanks for the tutorial!  Is that script really necessary?  I can already trigger the camera by the trainer switch on my Tx.  So if I set up the Mission Planner to send a servo signal on the same channel, won't that trigger the camera?  Or is there something else you're trying to accomplish with the script?

  • Im using ArduPlane. I believe its version 2.78 on the APM and 1.3.0 as well as 1.3.1 on Mission Planner. I guess Ill try reloading my APM firmware as much as I'd hate to. My plane is flying like a dream and just as soon as I reload the firmware on it... :(    Anyways, here's a pic just to show.. The list is in alphabetical order and as you can see, there is no Relay_Pin parameter. 3701728174?profile=original

  • I am having a similar issue to Jamie.  I can not find the RELAY_PIN in my parameter list either.  I can trigger the camera with my radio, and I can also trigger it by right clicking on the map and selecting trigger camera now, but I cannot get the automatic trigger camera by distance to function at all.  I am using arducopter and MP v 1.3.1.

  • It was in  ArduCopter V3.1.2, not sure about V3.1.3.

    RELAY_PIN value 13 = APM2 A9 pin

    I switched back to ArduCopter V3.1 and is also available with it.

    You might expand Jeff's images indicating the locations in full parameter list to make sure you are looking in the right place.

  • Yes I still have that parameter using even 3.0.2 released just a few days ago. And that's running Mission Planner version 1.2.99 I think. You're not using ArduCopter, right? I'm not sure about that, this is all in reference to ArduPlane.

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