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?

You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –


    • LOL. Where were you two months ago when I needed you. Thanks for your post it's much appreciated. Just about to start my business here in NZ.

    • Hi Ausdroid,

      I could not send my address to you by private message.

      Name: Plinio Augusto Araújo de Almeida
      Address: Av. Água Verde 1800 - Curitiba - Paraná - Brazil
      Zip Code:80240-070

      Best Regards,

      Plínio Augusto 

      • Hi Plino,

        Did you get it?

        Did it work for you?

    • Hi Ausdroid,

      I also would like to test your prototype CHDK cable. Below are some pictures of my drone with Canon Sx260 Câmera. I will send my address to you by private message.

      Best Regards,

      Plínio Augusto


      • Plinio,

        Have you receibved your cable?

        Is it working for you?



    • Hi Ausdroid

      I am very interested to test your prototype, at present I work with a big UAV (3.0 m wing span) mapping high lands in Andean Range Mountain. I use a Sony A7r and Sony a5100, but the Canon S100 is very useful in very high zones due to low payload restriction. As you can see in attach pictures, now I use a push servo as trigger, mount in 3D ABS frame, but it is not a dependable method, i lost many pictures due to random fails. I am in Lima, Peru. I hope you let me test your work...

      .kind regards

      Juan Pablo Gayoso



      • Juan,

        Have you received the cable?

        how has it worked?

        • Hi Joe

          I am in fieldwork time, but I consulted about my mailing in my city, and one package from Australia arrived the last friday. The sender is Andre Preller. I am pretty sure that is your shipmment. I am excite to review it. I am returnt to the city the next week. So I estimate that i be able to test it in two weeks, I hope. Sorry for this long period but This is a bussy time for me....Thank you so much for your confidence...

          • Juan,

            How did it go?

      • Juan,

        PM me with an address and I will send one over. Would LOVE to see some of the pictures. What a fantastic area to be flying in.


This reply was deleted.


Hiroki Tanaka liked Hiroki Tanaka's profile
Oct 13
Derrick Davies liked lisa TDrones's profile
Sep 23