Jeti CDI-Sensor

I stumbled on a plane with gasoline-engine and as a telemetry-freak I “needed” the propellers rpm. Kinda straight-forward, the CDI-box has a tachometer output and on top of that it’s opto-isolated so let’s make some telemetry with it.

Jeti CDI-Sensor

You need to jump into magnificent world of Ebay once again, parts needed:

  • Arduino Pro Mini 3.3V 8Mhz (Or equivalent) Example link to Ebay here.
  • One 2.4kΩ resistor
  • Little wire and shrink-wrap.


  • Shows engine RPM as reported by CDI-box


Connecting Jeti CDI-Sensor to CDI-box is easy:

  • Tachometer output brown wire -> Arduino GND
  • Tachometer output yellow wire -> Arduino pin 5

Check connections in pictures below.

You also need the connection to Jeti receiver:

  • Arduino pin 3 -> 2.4kΩ resistor AND receiver signal
  • Arduino pin 4 -> 2.4kΩ resistor
  • Arduino RAW -> Receiver positive
  • Arduino GND -> Receiver negative

NOTE: Some boards have GRN where my boards have GND. Do NOT use GRN, use GND!

If you wan’t to use Arduino Nano, read this post.

RCT CDI-Sensor Schematic

Programming Jeti CDI-Sensor

Go and get the suitable .hex or .ino (Named RCT_CDI) file from my Github here. Easiest method is XLoader + .hex-file. With Arduino and .ino you need to use the libraries included in Github repository. For info on how to use these look in RFID-sensor how-to here.


In the transmitter – Installation and Usage

Usage is really simple. Due the way rpm is calculated Arduino is slow on sending sensor-names. That is why for the first 15 seconds after power-up sensor does not count rpm. Easiest way to install is to in transmitter go to “Main Menu” -> “Timers/Sensors” -> “Sensors/Logging Setup” and then power up the model. You should see one added sensor “RCT CDI” with one telemetry-value “RPM”:

After that you can have the engine rpm displayed on main screen (up left):

There is also a Jetibox screen but since no settings are needed it’s just a static screen:

That’s it. really simple!

Important note! – Testing

Alltho this is opto-isolated we need to remember that engines may give disturbances to RX. So make sure to test thoroughly with range-check with engine running on various speeds. Remember safety with propellers!

Tested with DLA20RA + CB200 + DC-24 fw 4.23.

Version history

  • 1.0 Initial release


Always make sure everything works as it should. Do not use faulty devices. neither RC-Thoughts and/or me are in any way liable or responsible for anything you do with your equipment or to others with equipment used as described here. You should never use LUA-apps for operation-critical functions.

If you find something that is not working or is behaving strangely please let me know. I’m a car-mechanic by training, not a programmer-geek :)

Most important thing

Is to have fun building, this will not bankrupt you in any way :)