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.
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.
- 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 :)