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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Hi Martin.

Yes 0.5w is fine as there is hardly any load .. you can mount everything to a small piece of proto board or just solder the legs of the components and use heat shrink.

Hi Zoom ..No Worries ..Just send me your details.

Rueben, any chance you can sell me one plus shipping?

I've built and tested Marco's circuit.  It works.  I'm giving up on the Sparkfun device until someone can post a wire diagram that has been tested and proven to work.  Unfortunately I don't have a lot of time for experimentation.  I'm going to flight test with Marco's circuit after Christmas, it should be fine.


Nice! ;-)


I've built Marco's design as well. It works very well on my hexacopter. However your drawing is very clean compared to the way I built on freehand on protoboard. Great job laying it out. Now I want to build a couple more following your layout.

Thanks for sharing.

And thank you Marco for sharing so many month ago. 

Can't take credit for the diagram, that was posted by Thorsten back on page 6 of this thread :-)

He also posted pictures.


Hi Bill ..you just need to pay the postage .. I don't mind helping out ..One thing though .. would you guys be expecting a camera plug on the other end ? If you do, I will have to find the correct plug and schematic for Canon.. I dont use canon Cameras I use Sony NEX ..

Hi Reuben,

Currently I'm also using nex5 for mapping with IR trigger that sometime misses the shoot.

Do you use USB trigger on your nex camera with that cable ?
Do you mind to produce the cable for me?

Many thanks in advance.

Hi Reuben, I can order a cable for the canon from ebay and have it shipped to you.  This thread shows the cable and the modification for APM 2.5/2.6:


Hi Waladi 

Yes, I use the usb trigger on my NEX. I find it better and more reliable to use. If you want you can make the cable just use the Turnigy Rc switch its really easy .. you would just need the special usb for NEX it is not the standard Mini B usb cable.. I can do everything for you, but I would have to buy the parts from china and it will take a while for them to arrive.. 

let me know if you want me to proceed.

I guess I will also wait to hear if anymore people want cables before i order the parts ..



Ok seems there is some interest in trigger cables. WHO WANTS ONE !  speak now or forever hold your peace.  lol

Regards Reuben

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