shift light

We may earn a small commission from affiliate links and paid advertisements. Terms


i want to make a shift light/beep so that i dont have to look at the gauge to know when to shift, question is how do i read RPM?

how does the ECU know what RPM it is at? there most be some wire that has RPM on it but i cant seem to figure out which one on a p30 ECU.

p30 ecu pinout



the RPM is usually a square wave output
looks something like this
   ___     ____     High
__|   |____|    |___  Low

The peak or part that goes up is called a high. it's usually a
pulse from 0 to +5vdc . You'll need to read this wave . as RPM increases the spacing between the waves gets closer.
you'll need to be able to sense the change in frequency to track the RPM. if you can do this you'll be able to make something beep at a certain RPM.

It isn't as simple as just hooking something up. You'll need to develop some type of electronics to do it. You'll need a frequency to voltage converter. and you'll need to trigger a relay (at whatever voltage correlates to the frequency produced at whatever shift point you want to shift at) to enable the buzzer to work.

The easiest way would be to use the signal from the sift light itself. and hook a buzzer or something that will emit a sound in parellel with the shift light.
when the shift light lights up the buzzer will go off.
oh, i know how to do it, i can read pulse width modualtion through a PIC processor and have all the controls i want,

but where is the signal to read RPM from the ECU(what pin) or engin(where)?

thanks, :)