I made my own “multi-sensor” for the FrSky radio system. An Arduino Nano reads a few different sensors and sends all the data to the Smart-Port connector on the RC receiver. This way I can get information such as battery voltage, speed, altitude, GPS position, and temperatures on my RC Radio when I fly my RC planes. This is perfect for planes that don’t have a flight controller onboard.

My design and hardware is based on the FrSky library from Pawelsky: https://www.rcgroups.com/forums/showthread.php?2245978-FrSky-S-Port-telemetry-library-easy-to-use-and-configurable

I actually started experimenting with making my own telemetry sensors a few years ago. Therefore my code is actually quite old. Back then, this was the only library available. I still think it works well, but today there are also other alternatives available.

At first, I just soldered a GPS and a servo connector to an Arduino NANO. But later I made a few PCBs to make them easier to assemble. My first versions had voltage monitoring of the individual cells in the flight battery, but I found that it was annoying having to plug in the balance connector of the battery in the plane.

This is my third iteration of the board. It has a single input for LiPo battery voltage monitoring with a voltage divider and filter capacitor, a BMP280 barometer for altitude and variometer measurements, a connection for a Beitian BN-220 GPS or any other NEMA capable GPS for speed and position data, and two Dallas DS18B20 temperature sensors, one onboard and one attached with cables.

Update 2022-01-07: I fixed an error in the PCB design and made a few small adjustments in the code. The links are now the updated versions.

Link to my schematic and PCB: https://oshwlab.com/Axbri/frsky-telemetry-v3

Download link for my code, schematic and PCB gerber-files:
Axels FrSky tememetry sensor V4.zip