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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              • I see the problem, there must be multiple types of SparkFun converters, the one I received does not have a place to provide 5V from the servo rail. See photo below.


                • The picture shows the same one I have.  Is there another one?  I thought that supplying 5v to the servo rails via BEC (which is what I'm doing) would boost the current on the 3.3V Pixhawk output signal enough to make this device (Sparkfun) put out a clean 5v signal on the output (middle "5V OUT" connection).  Not true?

                  I'm simply connecting:

                  1. Pixhawk 3.3v (AUX OUT #5) "signal" output to the "1-4V IN" on the Sparkfun
                  2. "5V OUT" on Sparkfun to positive USB (Canon camera)
                  3. Pixhawk 3.3v negative to "GND" on Sparkfun and negative USB Canon (common gnd)

                  Is this not correct?

                  With a multimeter on #2 and #3 above, I am *not* seeing a 5v signal.

                  • Developer

                    >>> I thought that supplying 5v to the servo rails via BEC (which is what I'm doing) would boost the current on the 3.3V Pixhawk output signal enough to make this 

                    No. The two are not related.  The 3v3 output will remain at 3v3

                    You need to connect the level shifter to +5, signal, and Ground

                  • Gary,

                    After I posted the picture of the SparkFun converter I have I went looking for one with a separate 5v input. There isn't one on the SparkFun website. Then I thought that perhaps Craig really meant that the 5v should be connected to the Pixhawk as you did and not the converter, but that clearly doesn't work.


                    Perhaps you can show us a picture of the the one that works on all the vehicles there along with a wiring diagram. 

    • Paul,

      I feel your pain.

      I haven't read the rest of this thread, but have you established that you are getting a voltage at the pins? i.e., when you activate the switch on your TX, do you get 3.3V at the desired pin?

      There  are a number of things that need to be set such as the relationship between the input channel and the output channel (aux pin).

      My settings are;

      CAM_TRIGG_TYPE  is set to Servo

      CH7_Opt is set to camera trigger

      RC10_FUNCTION is set to Camera Trigger

      CAM_DURATION is set to 1 second

      CAM_SSERVO_OFF is set to 968

      CAM_SERVO_ON is set to 2070

      If you can see 3.3V at the pin when you want to trigger, then the issue is with the cable.

      I have just received the Sparkfun step ups, so I will let you know how I go with them.

  • Ok easy solution just use the Turnigy switch has PWM input trigger and you can have any voltage from 1-30v .. for chdk just tap into the 5volts from the servo wire going to Aux channel on the the pixhawk ..I will post a schematic if someone is interested.

    Cheers Reuben 

    • Hi Reuben

      Iam interested in looking at your schematic

      Do wish some one would just make a pixhawk ChDk Cable with circuitry built in

      Any one know if 3D robotics is going to make & sell one or any other premade

      was thinking 3DR must have solution that there using on the X8-M it uses pixhawk with a canon Sx260


      • Hi Zoom 

        Yes its pretty easy, just use an RC switch and if you need to short the two pins on a camera, do as the picture shows , or you can send 5v to the camera such as CHDK requires just follow the other picture (by adding a 5v line from the pixhawk to one side of the fet) Red line in the picture. Remember to set in MP to use the aux out set as "servo"..easy as that.

        Cheers Reuben3702677800?profile=original3702677967?profile=originaln

        • Hi Ruben,

          I have just found this. I am interested in your first picture and it makes sense to a certain point.

          I need to short two wires only to get my Samsung camera to trigger. I am however not sure which of the two wires are actually shorted.

          Is it the signal wire and the ground wire?

          Kind regards


  • You have to choose between RC control (pass through) or APM control.
    Use 10 for APM control or 0 for RC Pass Through.
This reply was deleted.


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