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?

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        • The circuit that uses two transistors ( BC547 &  BC557 ) is needed when the camera ground (0V) must be at the same potential as the pixhawk.  Apparently Sony cameras need this while Canon Powershots do not.  So the Powershots can use a "floating ground" approach and thus a simpler one transistor circuit.

        • And is it possible to add an LED to show it is receiving/passing signal!

          •  Reply by Sandy Sound 9 hours ago

            And is it possible to add an LED to show it is receiving/passing signal!

            If you want to add an LED, change R2 to 1K ohms and put the LED in series with it.  Connect the camera across the combined R2 & LED circuit.

  • Hey guys, have a complete ''Plug & Play'' solution for you that support over 100+ camera models and multiple brands. Features ON/OFF function for Sony MULTI equipped cameras and multiple trigger modes. No need to make custom DIY solutions and they could end up damaging your equipment and costing as much as complete solutions. 

    Check out Seagull MAP @
    Don't forget to use 10% discount coupon: DIYDRONES

    Hope you found this to be helpful :)

    • Nice looking solution.

      But at $75 US$ (plus international shipping) it's going to be a lot more expensive than the simple one or two transistor DYI solutions proposed here.  Still,  there is some value to a pre-built solution.

      Unfortunately,  it appears like this device will only work with a few of the more expensive Canon "point & shoot" cameras (i.e. larger ones with a jack for an external shutter release device).  It won't work with the smaller Canons that you would want to use on a UAV (with CHDK and a suitable UAV specific script).  So a DYI cable (or one of several other commercial solutions) is still the way to go there.

      • Hi Walter,

        If you choose Priority Letter shipping method, the price is around $43 to the U.S - or around $53 if shipped with registered mail w/ track & trace.. :)

        Orders to the U.S will arrive within 3-6 weekdays + customs time. :)

        • Thanks for that note.  That means the total cost to someone on the west side of the Atlantic comes to about $115 US$ then.

          • Not exactly... ;) the prices mentioned above is the total at checkout for one Seagull #MAP with camera cable after choice :)

  • Juan Pablo, Plinio,

    I will send the cables on Friday and send you tracking numbers.

    Can you both still;

    1) Make a friend request.

    2) Private Message Me



  • We have also developed a CHDK cable to be packaged with a mapping drone we are about to release. Our preproduction prototypes are in and we are currently testing them. We have a few extra if anyone is looking for a CHDK cable for mapping. I would be happy to send a few out at no cost provided we get feedback.

    If anyone wants one, please PM me and send me a photo of your drone, ready to fly with canon camera installed. I only have 5 to send out so first in.....

    I have attached our draft manual which may be of interest (and may be completely wrong)!

    Triggering CHDK from Pixhawk.pdf
This reply was deleted.


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