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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Could you post a picture of the tuffwing cable and bec connections? It would be really helpful to see how they connect to the pixhawk.

I am using a 4-in-1 25A ESC (http://www.hobbywing.com/product_show.asp?id=292). It has a 3A/5v Switch BEC. Does it mean that I am stealing 5v from the Pixhawk and running into the risk of a brownout?

If you're using the 3DR power module then everything is OK.

Anyway, the current consumption of the trigger is very small. There is no risk of a brownout.

Check this link for instructions on how to connect the cable and set it up in Mission Planner.


To see (or order) the cable, scroll down this page to UAV Mapper Parts from the following link


Here's a pic.

I have tested the cable with a 5 volt UBEC and with 4 Afro ESC's with 0.5A linear BEC's. It works both ways. The UBEC gave me 5.33 volts on the AUX OUT rails, the linear BEC's gave me 5.03 volts on the AUX OUT rails.

I had the UBEC pluged into AUX OUT 6.

Here's a pic of the TuffWing cable connected to AUX OUT 5 on my Pixhawk. The Afro ESC's have 0.5A linear BEC's that give me 5.03 volts on the AUX OUT rails.

Hi Bill

I've added this cable to the end of the CHDK wiki page here. I figure no point reproducing your user guide in a dedicated page ... and this is the first place people looking for a chdk solution on the wiki will go.

OK by you?



OK by me.

Thanks Hamsih,


HighYoyo: is magical... ;-)

But it's huge!

Hi Marco , Bill and Iskess

Sorry Guys I have been away ! One of my elderly family members has been seriously ill and It was time for me to leave my country of residence and travel overseas to take care of business .. But now I am back at home with a lot of Catching up to do .. 

I will be sending Bill and Iskess some new updated cables soon , I have now received my special icomm module, this cable will be able to do Sony and Canon cameras. Actually the unit will be very small You can see the module on top of a servo plug for size comparison! I also have received the Sony S2 Usb plugs I ordered too .. plenty of parcels waiting for me when I returned home ! 

Best Regards


12 grams

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