Using AUX pins as relays for CHDK

I'm confused and a bit frustrated, would appreciate any help as I'm not sure how to proceed.

Setup: I have a pixhawk autopilot running Arduplane 2.77, using Mission Planner 1.2.95

I've been following this guide to get my CHDK enabled camera working with my pixhawk. I'm interested in getting the camera triggering based on distance traveled.

Obviously the guide was written with APM in mind, so it needs to be adapted a bit for pixhawk; specifically the setting for RELAY_PIN. I've kept the rest of the settings the same as in the tutorial.

Pixhawk has 6 AUX ports according to the quick start guide, I am assuming that the numbers above the pins correspond to the AUX port numbering. When you mouse over the RELAY_PIN parameter, it says that pin 54 corresponds to Pixhawk FMU AUX1.

Tried setting RELAY_PIN to 54, no joy. Did a bit more looking, discovered in the release notes for 2.77: 

"Improved relay code
The relay and servo set code has had a major overhaul, with up to 4 relays now supported for MAVLink control and much better support for the DO_SET_SERVO, DO_SET_RELAY, DO_REPEAT_SERVO and DO_REPEAT_RELAY MAVLink commands. Along with these changes is a new parameter BRD_PWM_COUNT which allows you to specify how many auxillary PWM outputs to enable, with the remaining outputs being available as digital relays. This allows you to re-assign some of the aux servo outputs on Pixhawk for use as relays, by setting the RELAY_PIN, RELAY_PIN2, RELAY_PIN3 and RELAY_PIN4 parameters. The pin numbers for these pins start at 50 for the first aux servo pin, and go to 55 on Pixhawk."

Additionally,I found this github issue about this same problem that states that the Pixhawk can't trigger CHDK because its relay pins operate at 3.3V instead of 5V.

So i suppose my specific questions are:

1) Is AUX1 pin 50 or 54?

2) Can anyone confirm that the relays, when working properly, won't be able to trigger CHDK?

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        • Previously I am following this method for APM :

          I try for Pixhawk and it's work after trial and error with cable connection...

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          • Follofwing the discussion from the first and doing the test myself using a voltmeter, when triggered the signal pin giving a 3.3v while the middle pin (+) giving ~5v when triggered.

            I think you follow the method differently. Most of us (and of course the one on the link that you mention) connecting the Red usb cable to signal pin and black cable to the ground pin on the pixhawk, while from your photos, you are connecting the red usb cable (+5) to middle pin on pixhawk (+5). Although it different, it shed a bright light.

            I have built marco's circuit and able to perfectly trigger my camera on pixhawk same as apm did. But using your approach will save a bit more space on my tiny quad as there's no circuit required. Will try this method tonight to see if it's working on me as well.

  • Hello mates,

    I'm a total electronics ignorant so I'm unable to do my own cable to trigger my Canon SX260HS from Pixhawk. Would any compassionate soul of you be willing to sell me one of these trigger cables? (I live in Spain and of course I would assume all the reasonable costs/pricing).

    Does the gentwire-usb cable work for pixhawk without need of additional step-ups or similar circuitry? I can buy one but I'm not sure if it works as my knowledge about electronics is certainly limited.

    Thank you very very much

    • I've tested this Ricoh trigger and it works with CHDK on the SX260.
      CHDK has a setting for this triggering protocol.
      This is triggered off an RC out and works the same on PH or APM with no voltage issues.
      • iskess,

        If I'm reading the description of the Ricoh trigger correctly (, Robert will need to supply 5 volts on the Pixhawk power rail (since the Pixhawk doesn't supply its own) and will need to learn how to used CHDK along with the script for interpreting PWM signals (tutorial here:

        Is that correct? Do you already have a CHDK script that works with this trigger that you can share?

        Ricoh Switch
        • It's been a long time, I no longer use the Canon. Yes, the servo rail must be powered with 5 volts, I fly planes so that was never a thought. It did not require a special script. There was an option already built into the CHDK menu to use different triggering protocols. Ricoh's was one of those options.
          • iskess and Robert,

            OK, after doing some searching I found here (  that you need to go to the CHDK main Menu > CHDK Settings > Remote Parameters >Switch Type and set it to CA-1

            Good Luck!

            • Phill and Iskess,

              I thank you so much for looking into this. I initially thought it was enough with this cable and I didn't have to supply the 5V anyhow. Could you please tell me where exactly I will have to plug a 5V battery?

              Regarding the script, I intended to use the one provided by 3DR:

              Among its triggering options are USB and PWM (as well as intervalometer, etc.). Thanks Phill for telling me I will also need to set the switch type to CA-1!

              • Robert,

                About four posts above your first post is the discussion about connecting a 5 volt UBEC to the Pixhawk servo rail, that's what you (or a electronics knowledgeable friend) needs to do.

                With regards to the script, it seems needlessly complex to me if all you want to do is trigger the shutter. I don't think you'll need to set the switch type to CA-1 if you use the script since it's monitoring the PWM pulses directly and determining which of the 6 functions it's going to perform.

                • Actually,  while setting the output type to CA-1 is wrong for what you are doing, it also will not hurt.  When CHDK is running a script, the USB remote setup values for input and output types in the CHDK menus are ignored.

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