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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Replies

    • Thanks.  I'm still looking to prevent people from wasting time trying to get the Sparkfun device to work, since (like me) they might just look at the Wiki and assume (like me) that it will work in the way you would expect.

      Craig?  We're all busy, but we should be trying not to waste each others' time.  We just need a simple connection drawing, which should also be added to the Wiki.

      I'm attaching a diagram of the first connection method I tried, which I could not get to work.  This seemed to be the intuitive (or read naive :-) method.  Power supplied to the rails via BEC.3702537803?profile=original

      Gary

      • Developer

        Gary, you have the signal out of the Pixhawk connected to the +5V.  That is not going to work for you.  I recommend trying this level shifter https://www.sparkfun.com/products/12009

        SparkFun Logic Level Converter - Bi-Directional
        The SparkFun bi-directional logic level converter is a small device that safely steps down 5V signals to 3.3V AND steps up 3.3V to 5V at the same tim…
        • Gary,

          I've built Marco's design as well. It works very well on my hexacopter. However your drawing is very clean compared to the way I built on freehand on protoboard. Great job laying it out. Now I want to build a couple more following your layout.

          Thanks for sharing.

          And thank you Marco for sharing so many month ago. 

        • I've built and tested Marco's circuit.  It works.  I'm giving up on the Sparkfun device until someone can post a wire diagram that has been tested and proven to work.  Unfortunately I don't have a lot of time for experimentation.  3702773588?profile=originalI'm going to flight test with Marco's circuit after Christmas, it should be fine.

          Gary

          • Ηι,

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

            Thanks

          • Developer

            Nice! ;-)

            • Can't take credit for the diagram, that was posted by Thorsten back on page 6 of this thread :-)

              He also posted pictures.

              Gary

  • Replying to Craig Elder's post:

    I wrote:

    >>> 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

    Craig wrote:

    >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

    Craig -- sorry but I'm not following you.  Your description above is not sufficient to know how to wire this thing.  You have to realize that a lot of us are not electronics experts.  The diagrams of Marco's circuit helped because it showed exactly how to wire it up, and despite being more complicated, I was able to get it to work.

    So -- here is another (failed) attempt to wire up the Sparkfun device.  It doesn't work.  All I see is a constant 5V on the output.  Can someone (Craig?) please post a wire diagram of exactly how you are connecting this device, or at least look at my diagram and tell us what is wrong?

    Gary3701897027?profile=original

  • Good post.  You should be selling these for $6 each.  A tax on non-googling things I guess.

    What's all this trying to ghetto together a "relay" talk anyways?  Just get a real relay!  They're less than $1.

    • Can't believe someone is not selling these (3DR)!!!

This reply was deleted.

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