Hi together,

i want to use a D4R-II together with APM2, PPM and RSSI are no problem. What i want to connect as well is 

the serial port of RX and APM2 to send compressed GPS information over the FrSky data downlink to my antenna tracker. in principle i have that working, currently with an arduino pro mini evaluating an attached GPS sensor, compressing the GPS data and sending it over the downlink. So tweaking arducopters software to do that as well will be no big deal. I use NewSoftSerial with the arduino as it provides the inverted TTL signal, that is expected from the FrSky RX.

Question now is:

1) Can FastSerial in Arducopter 2.6 somehow be used for generating an INVERTED TTL signal?

2) Which Pins/Port should i use on the APM2 to connect the FrSky RX serial port?



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You don't want to be using oddball signals.  It's a bad idea.  

Very interesting topic as I wanted to get this working as well.

Problem is I believe we don't have enough processing power left on the APM to run NewSoftSerial.

I have heard however, that it can simply be inverted using hardware?  Simply use a transistor?  But I stopped there as I have too many project on the go and this started getting too complicated.

@Jake: what do you mean by oddball signals? Never heard of that phrase, but i am not a native speaker though...

@R_Levebre: Jupp, using an transistor inverter, thats another option. I just thought it might be possible to enhance FastSerial, that it can handle inverted signals. I agree using NewSoftSerial is not an option.

Will keep you posted.

Im going to try this with my mini.. slightly different setup tho. I have been planning using the mini as an i2c interface port to the AMP1 for the sonar digital port. ie. sonar ->digital out -> Mini -> i2c -> APM.

would be nice to have just the GPS data going to the RX - as its not fast enough for the whole kit and kaboodle in the mavlink data on the uart port.

I wonder what the best way to get the data would be? listening to the GPS when it sends data to the APM would be the least intrusive and wouldnt involve any changes on the apm side. but is that possible with i2c? or would it tie up the mini too much waiting for data like that?

Chris, my one and only goal with this concept is to transmit data to the FrSky Tx using the FrSky Telemetry Hub protocol.  That way I can simply plug in the FrSky Telemetry Display on my radio and see the data on my Tx, just as if I had a Telemetry Hub installed on the plane.  I just want something simple that allows me to see speed, G-Froce, etc, while flying.  I don't want anything more complicated than that as I already have an Xbee/3DRadio, etc.

Ok, now i ran into a problem it thought would not happen....

The CPPM Mode of neither D4R-II nor D8R-SP works with the Arducopter 2.6 Firmware on APM2....ARGH

Tried both variants:

1) Bridged signal input pins 2 + 3 and connected sum signal to chanel 1 input: Result NOTHING

2) soldered the liddle bridge ppm->-->Ch5 and connected sum signal to Channel 5 Input on APM2: Result NOTHING.

Any Ideas on that?

I am currently using D4R-II with Flyduino / MPNG without issues.

You must bridge 3+4, not 2+3. PPM will be output on CH1

For D8RSP you already have CPPM on ch8 by design without any bridge.

Of course i bridged 3+4 on the reciever to get PPM OUT. The reciever works, i can confirm that.

What i mentioned above under 1) is bridging the INPUT pins of the APM2.

So the APM2 is not accepting the PPM signal. From the LED it seems to be fine, but i do not get any movement in the mission planner.

Un soldered the bride ppm. It doesn't need that to have CPPM to work.

I just removed the bridge mine and it's still not doing anything.

Hmmm... I'll have to look at this.  I have used PPM input from a D4R, D8R, D8R-II, and D8R-SP.  No problem.  I have a D4R-II, but I don't think I've actually fired it up yet.  I'll let you know what I find.

I'm pretty sure you're just doing something wrong.

Did you figure this out? I just soldered the bridge on my APM 2 and I don't seem to be getting anything from my D4R.  


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