A simple but usefull build to send two voltages and rpm to an frsky receiver.

this code relies heavily on this up-stream s.port project https://github.com/RealTadango/FrSky/blob/master/examples/SimpleSensor/SimpleSensor.ino you will need to add his libraries to your arduoino environment for it to work.

Measuring voltage will need voltage dividers - you cannot send more than 3v to the arduino A pins. Suggested divider ration is 10k / 2k. This will be sufficient for a 2s lipo to be used for the pack and ignition system.

Most CDI units will output 5v to the signal line. This is too high for for some arduinoboards.
A 10K resistor on the RPM pin line will drop the 5v down to 3v.