Frsky D4R-II 8 channels receiver with telemetry part1: data search

 This is an old receiver, you can still find the spec on web:

https://www.frsky-rc.com/product/d4r-ii/

Compatible with FrSky two way telemetry modules: DFT, DJT, DHT, DHT-U

manual: https://www.frsky-rc.com/wp-content/uploads/2017/07/Manual/D4R-II.pdf

If you jump CH3/4 signal pins with a jumper, it out put CPPM on ch1 and RSSI on CH2

push the button and power up, it will goes into bind mode, The I turn on my T18, select:

protocol Frsky D8 and press bind, it binds ok!

I have a invert cable for the telemetry port, this receiver  is the one in iris with a pixhawk(FMUV2, which px4 refer to Pixhawk 1).

But now a day, there is not much information on this receiver.

I remember read about a D port but now what have is this page:

https://docs.px4.io/main/en/peripherals/frsky_telemetry.html

Also ardupilot has some info, descript the data contain by D and S port protocol

https://ardupilot.org/plane/docs/common-frsky-protocol-info.html

The serial mapping is confusing:

https://docs.px4.io/main/en/flight_controller/pixhawk.html#serial-port-mapping

Pixhawk FMUv2 / Cube FMU v3 Serial Mapping

Sport lib for arduino

https://github.com/RealTadango/FrSky

2015 for X and Dport:

https://www.rcgroups.com/forums/showthread.php?2394886-LDU-as-FrSky-Telemetry-sensor

for D port:

https://www.rcgroups.com/forums/showthread.php?1874973-DIY-altimeter-for-FrSky-telemetry-receivers-with-Arduino-BMP085#post24749934

this confirm me that the baud is 9600

There was lot generation of telemetry with frsky, in this doc,

https://ardupilot.org/copter/docs/common-frsky-protocol-info.html

 it class into repurposed frsky telemetry (D and Smartport) and passthrough frsky telemetry(smart port)

So, I set the Serial2(telemetry2) to 9600, frsky D, I first want to know what are the information sent by pixhawk, so I connect it to pc with ftdi and found:

based on the code in the above link, 5E is the start byte, and following the data type:

But, base on what I found: this FrSky document 

it says:

for temp1 andtemp2:

https://docs.px4.io/main/en/peripherals/frsky_telemetry.html#d-port

temp1 is for flight mode and temp2 is for gps info as in S.port

here is how these 2 are decoded: https://github.com/Clooney82/MavLink_FrSkySPort/wiki/1.2.-FrSky-Taranis-Telemetry

a new one with https://github.com/zs6buj/MavlinkToPassthru

Tmp1	GPS status = ap_sat_visible*10) + ap_fixtype

Tmp2	Armed Status and Mavlink Messages :- 16 bit value: bit 1: armed - bit 2-5: severity +1 (0 means no message - bit 6-15: number representing a specific text

 

Today, with jumper T18, I have yaapu lua, but it does not support D port, only Sport.

 Inav lua still work with D port. But I did a test on it. pixhawk has gps fix, and using openTX discover new sensor, it does found gps data such as lat, lon.

But iNAV lua does not show it, but heading voltage is correct.

Sensor discovered in gps fix:

totally 16 sensors, I believe 1-6 comes from receiver itself.

Here is how to decode Dport with arduino:

https://ceptimus.co.uk/index.php/2017/04/21/decoding-frsky-telemetry-data-with-an-arduino/

the signal of output of TX pin of module is inverted, also the voltage need to be take cared. it use interrupt to handle the invert of signal.

it says that the packet header starts with 7E, from module on transmitter