read gas engine rpm from cdi to my radio by RP2040 #102

[xiaoyigg]

My DLE55 gas engine works with cdi ignition which has a connection(3 wires like servo connection) to an external tachometer (rpm meter).
How can I connect the ignition box to the arduino to get the rpm then send to my radio(Frsky X18 ethos and TD R10 receiver)