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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SO the only route is to build one?

I really had hopes for the gentWire USB2! Anyone else guys that did have some luck with it?

Hi thre,

is it easy to configure? You just need to go to pixhawk camera gimbal menu, set the PWM values and then set these values as shutter range for triggering the camera's shutter? 

Hi Reuben - is this still an offer?

I was delighted to to find your solution and ordered all the bits from ebay and dug out the old solder iron. 2 days later with burnt and cut fingers i realise my eyesight is just not what it was. I have made 3 types including the EFL600 LED version and none will work but I'm not sure if it is my workmanship?

It may be that there is some other problem but I can get my Canon to shoot with a plain USB connection when i unplug it. I have installed a BEC.

Am happy to pay - just want it to work now

David :-)

Yes quite easy: setting the PWM value on MP and setting the stratosnapper using their smart tool according to your camera type.
Try to lower the PWM value if it try to trigger continuously.

I prefer to use the WIRE type trigger eventhough Stratosnapper also support IR trigger.
It's more reliable to trigger compare with the IR shutter type.

I seconf to that... But if you're aiming to trigger canon camera, i think Marco's circuit with CHDK work perfectly with only $1 cost.

Hi there,

thanks very much for the input. So I guess that I connect the USB to servo cable directly on the strattosnaper, correst? Using two wirew only, ground and signal, yes?

Hello and thanks for the help.

I will try to take the schematic to a shop nearby and see if they can make it for me.


Can someone help me with this please. I have been able to get this to work with a Pixhawk and Marco's circuit but the only value returned by get_usb_power() is 116.

The WIKI suggests I should get a value between 5 and 16 but as I get 116 I get an error message.

if k < 5 then gosub "ch1up"
if k > 4 and k < 8 then gosub "ch1mid"
if k > 7 and k < 11 then gosub "ch1down"
if k > 10 and k < 14 then gosub "ch2up"
if k > 13 and k < 17 then gosub "ch2mid"
if k > 16 and k < 20 then gosub "ch2down"

To get going I have modified the script to execute the command I want when the a value of 116 is returned so its working for me now..

However I would like the ability to execute different routines. Can some point me in the right direction so that I get correct values from the get_usb_power() function. I am using a Canon A2400 IS camera with CHDK 1.3




Have you connected a USB cable to the +3.3V output? If yes, which wires did you use please?



I want to  trigger my camera with Pixhawk by CHDK such as your method.

So, I try to make a cable myself such as attach files. Is that right?

And the setting of MP is 

  • RELAY_PIN: 54

And the connection of Pixhawk and my canon S100 also like attach files.

actually, I am not sure whether the connection is right or not...

The script of CHDK I use is E38_APM.bas.


The camera still cannot work, no matter how I try to do!!

Is there something wrong with CHDK or MP setting?

Is there something still need to set I ignore?



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What 4 trigger modes?
Will it work as a relay? Or is it only a PWM switch?

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