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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Bill, I made my own cable based on Marco's circuit. My pixhawk will take pictures even with the motors dissarmed. This includes arming with the remote and the arming button. Hope that helps.

No, it's not important with the "relay" function, only with "servo" option.
Check with a multimeter the "5V pulse output" in the "mini usb" port.

What pins do I test on the "mini usb". Could someone post a pic showing the contact points for the positive and negative when testing?

I'll be on the road for a few days and will get back into this when I return.

Thanks for the help everyone. What a wonderful community.


VCC and GROUND, of course.

Thanks for the clear graphic Marco.

Much appreciated.

I will check it out when I get home (Friday) and post my findings.

Hi all,

Thanks very much for the useful info. I myself have been trying to setup the Canon HS280 to be triggered by the Pixhawk that has a BEC 5V connected to AUX rail, with no luck. Since I am very bad in building circuits, I would like to confirm please that if I buy the 132 gentWIRE-USB2 Canon cable I will be able to trigger the camera with pixhawk flying in a predefined waypoint mission. This cable contains a circuit similar to what Marco advised?  Should this be cable be connected to the AUX ports or the relay ports?

I would also like your help if possible in understanding what is the difference between the pixhawk's AUX ports and the "relay" or "digital" ports.

Thanks very much for your help


I need to get a multimeter with smaller contacts. Anyway I checked the two wires coming into the back of the mini USB and the are getting a constant 5.33 volts.

The gentWIRE cable by itself doesn't work.


Thanks for the reply. You mean it is not sufficient to trigger the shutter . What else is needed with it?

Has anyone tested this using a strattosnapper?


I have a gentWIRE USB2 which some people claimed that it should work if provided with 5V. I also bought a cable called Intellishoot from Event38 which was supposed to solve the 3.3V to 5V issue to trigger the camera, but it hasn't worked so far. It's a money pit. 

My personal opinion: stratosnapper is the most suitable trigger since even it can work with the "most" complicated Sony S2 Multiport.

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