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 discovered that two changes have to be made to get this sequence to work on 3.1.5:

        1) All waypoint commands have to have at least a 1 second delay or else the subsequent DO command is skipped.

        2) Waypoints with zero Lat and Lon are treated in 3.1.5 as though you really do want to go the the Gulf of Guinea off the coast of Ghana, Africa, contrary to the description on the Wiki. The Wiki description should say "Beginning with Release 3.2, if left as zero it will hold the current location." You will need to load your current (or desired) location as the waypoints.

  • Finally got some time to test this circuit and it seems to work fine with power supplied by USB to the middle rail of the AUX pins. The plan is to use this in an RVJet and power it from the BEC/ESC. 

    I used 1/2" protoboard from Sparkfun and kynar wire which makes for a nice small package but it makes for tough soldering. I need to make another one but this time I'll use a 1" circle protoboard. Here's a couple pics taken before the cable was heatshrinked. 

    3701686308?profile=original

    3701686272?profile=original

    Anyone know if there's a BEC on the ESC board for the Iris?

    • It would be nice if 3DR made a cable for the Pixhawk for this purpose.

      • Hi guys, I have read all the forums about this issue and I cannot trigger my camera on any Aux port from my pixhawk.  I am running Arducopter 3.1.5 using this rc switch http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...

        I have tried many aux ports, different combinations of servo/relay, I have powered the aux bus with 5v with no joy.

        I am trying to trigger my CanonS100 with CHDK loaded.  The cable and rc switch combination works when triggered from my Wookong FC.

        Can anyone out there give me a hand to trouble shoot this problem please, 

        • I wish they would have considered this issue when they designed the Pixhawk.

          I probably would have opted for another APM instead of the Pixhawk had I realized this.

          • The issue is the ARM Cortex processor's output signal is 3.3 volts. However it is a very simple circuit to make work. I've built two with spare parts I had. I do think 3DR should make a trigger cable for this. They would sell off the shelf quickly.

            • I don't think it would hurt the sells of their Pixhawk either.

              I sent a message to Chris Anderson some time ago about 3DR providing the cable. He replied on April 1 that it was on it's way. Guess it's not a big priority for them. Wish someone else would go ahead and make them available.

              • Developer

                We are trying to get them in the store as fast as we can get them made. 

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