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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The risk is that there is some mistake in your wiring or defect in one of the components that affects the 5V source. If your source is the same source as used by your flight controller you will fall from the sky. Small BECs are cheap and light and well worth the price to get some redundancy.

Hi Craig,

Did these ever become available in the store?

This is a real Pixhawk killer for me. The APM does everything I need without modification.

@Phil, yes that's what I thought. I just saw the soldering pads on the PM... Thanks!

Sorry not yet Bill.  I have sent your request to the people who decide what products go into the store.  In the mean time, you can buy one from http://www.gentles.ltd.uk/buy.htm?i=131%20gentWIRE-USB%20Canon%20SX...

For example, the Wookong inserts a yellow triangle on the flight path during flight when the flight controller instructs the camera to shoot. Would be really nice on a 1 hour mapping mission that at least the camera is being triggered, thanks Kyle

Hi all,

here is my layout based on Marco's circuit:

I hope it helps. Since there is no "official" solution so far, maybe someone can put this on the wiki page.

Kind regards,


Hi Bill,

I just posted a layout based on Marco's suggestion. If you have a soldering iron it is much cheaper compared to the gentWIRE cable. 

Kind regards,


Hi all,

below you find some photos of the making of my Pixhawk CHDK cable.

Kind regards,




Cut and bend:

Place the cables:

Solder and cut:



Hi all,

this is just to confirm that it also works with dual camera setups.



What model camera are you using and do you have the blurring problems that have been reported with the S95 and S100? I have blurring with my S100 on a hex so I've given up on using that one.

You might consider adding an LED/resistor across the output for trouble shooting. It's sometimes hard to tell if there is a problem with the Pixhawk configuration or the camera configuration. There's an intermittent problem that CAM_TRIGG_Type will sometimes be reset to "0" from "1" and the LED helps troubleshoot that problem.


these are my new S110. I'll make some first tests with these next week. Normally I am using the ELPH 110 HS without blurring. So I hope the S110 are fine too. I'll report.

Kind regards,


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