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Permalink Reply by John on March 11, 2012 at 7:13am

I used this mod for use with modified Mikrokopter firmware.

http://www.mikrokopter.us/index.php/topic,3125.0.html

It works great but I really would like an SBUS to PPM converter. There was a guy (sebastian) on the Mikrokopter forums that made one and it was hit or miss if the one you got worked (Mine didn't). The code etc is online and open source. I really would like to see a reliable one available. I would buy several.

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Permalink Reply by Mike Estee on March 11, 2012 at 11:53am

Yeah, I checked out his code. It was pretty unreliable for me too, he tried to avoid adding a hex inverter by using one of the pins as an interrupt driven inverter. (Pretty clever actually.) I found it to be *very* susceptible to timing irregularities though. However, I was using a 16MHz part, so it may be that the extra 4MHz made the difference.

Also, the raw SBUS values didn't appear to be normalized, but that may have been taken care of in the PPM out timing circuit (which I never got as far as testing).

I made a hex-inverter based version which works beautifully, but then started thinking about rolling a board and decided the shortest distance between me and having my APM2 running was to just code it into the firmware ;)

Are there other places where a S.BUS -> PPM converter would be useful? Would it be possible to have it up on the DIYDrones store? I think I'd probably be pretty flaky too if I had to do order fulfillment ;)

What about a simple S.BUS demux? That's pretty easy to do as well.

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Permalink Reply by John on March 11, 2012 at 12:28pm

The Eagle Tree OSD system is supposed to be PPM compatible soon. Even though there is the Mikrokopter hack, as new versions of firmware are released, there is no guarantee that the hacked firmware will continue to be updated. There has been conflicting info on whether or not MK will ever officially support SBUS. The last I heard was that it will.I plan on building an Ardupilot quad soon but will probably use my TSLRS which has PPM out. I know there have been quite a few people interested in the sbus to PPM converter but I am not sure how many have not found an alternative solution already.

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Permalink Reply by Ron Curry on March 29, 2012 at 9:43am

Mike,
Wow! This is very cool. I've been wanting to implement SBUS on APM 1 and 2 for a number of months and have dabbled at it but haven't spent any serious time or brainpower. Your work will help. I want to implement it in the on-board PPM encoder. Have you looked at that? Apparently you got it working but I'm loath to add more load on the APM's host processor - it's already underpowered.

Thanks,
Ron

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Permalink Reply by Mike Estee on March 29, 2012 at 4:21pm

Yeah, the PPM encoder is probably a better spot. SBUS runs at 100kbps, so it takes a really short interupt cycle to keep up. I'm seeing dropped packets from over-interrupted SBUS processing in the above posted code.

There's enough high priority stuff going on that it seems like support should be moved off into its own chip, like the spektrum adapter.

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