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Decoding LED indicator and sending via audio tx

Discussion in 'General Discussion' started by mroberts, Sep 15, 2013.

  1. mroberts

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    Anyone looking for a challenge?

    I was thinking it might be possible to tap into the signals going to the LED and send back an audio tone via a spare tx channel.

    There should be a number of the old LED modules floating around now, so there'd be some to test with.

    [​IMG]

    [​IMG]

    The theory is you tap into the board itself where its sending the red and green signal to the LED (I'm assuming you can't use the wires themselves as it looks like a serial setup to handle both LED out and USB I/O). Feed that into an Arduino, and based on the R/G/RG signal generate a n audio tone that you send down a spare audio channel - I don't know if anyone actually listens to their camera audio.

    You'd have a constant beeping, but you'd get BVR feedback of GPS loss and confirmation of which mode you're in.

    If you wanted to be super-speccy, you could throw in a DTMF encoder / decoder pair and build a visual indicator that mirrors what's flashing on the Phantom.
     
  2. marcus_canada

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    Or you could run a line of fibre optic line from the LED to the corner of your filed of view.
     
  3. mroberts

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    I'd originally rejected that idea because I fly on the same cam I record with, and didn't want a coloured light in the corner, but thinking abotu it more, that bit will likely get cut off by ProDrenalin in post.

    Adding a gimbal makes things problematic though.

    Would you just get an offcut of fibre from ?somewhere?
     
  4. Driffill

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    Jay, the creator of the FBOSD has look into this. He didn't say it was impossible, but if anyone could do it, it would have been him. A few things to remember, first of all, the led flashes for more than just what flight mode you are in, it also shows a bunch of data when starting up, as well as satellite and battery data while flying. Being able to program to ignore or skip those flashes would be quite impressive.

    Second, the flash codes DO change, so what ever you make to read these code would need to be firmware upgradable. I just updated my naza FW to 4.00 and now the flight mode indicator on the OSD is having a Fit . . . Until jay, or someone continuing the development updates the FBOSD FW to match the newer flash codes, it will probably stay faulty. To be able to "read" them, you need an good quality oscilloscope and good software writing skills

    Third, something jay had pointed out when being asked about tapping into the led and GPS wires going to the naza. You need to take in to consideration that anything you connect on those wire may cause undesirable results with the data being sent (I.E. tapping into the LED wires could affect/prevent the USB from working correctly) the data being transmitted via the 4 wire GPS Plug is a DJI proprietary code, and although it may be crack-able, being able to sell any device that uses that code would/could be illegal, and I'm sure DJI would be straight onto it. Hence the reason the FBOSD connect directly to the GPS puck.

    Lastly, only minor point, not all VTX's have the audio option, using the fibre optic mod is probably an easier and less complex method of archiving flight mode indication at the ground station.

    Having said all that, if one came out, I'd probably look into it, I can never have to much electronic gizmos :) I would have to upgrade my VTX to a 2 ch vid/Audio unit too.
     
  5. mroberts

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    Hmm.

    My assumption is that there would be a small microcontroller on the board that decodes the signals to the LED, which means you should be able to monkey with the LED itself without feeding back anything untoward into the system.

    If you're interfacing at the LED end of the system, that's theoretically public domain in the sense that DJI publishes the LED codes. All I was suggesting was three tones that signified red / green / yellow, which certainly would be a cacophony on startup, but would then settle down. Having a system that decoded "green green" to "GPS mode, 6+ satellites" would be nice but a lot harder.

    I wonder if you could do it from outside with two LDRs and appropriate filters instead - tape them right up against the LED cover so there's not much additional light.