I have begin a electronic project who can measure real time air temp,water temp,boost pressure and also rpm.
I use 4x20 lcd display with microprossesor and temp,pressure, sensor.
Soon I post and pics.
But how I can measure the rpm of engine?
I hear that you can take the rpm from diagnostic box but I am not sure.

 

Check this thread, it might have the info you require:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/help-w-shift-light-pill-225183/

 

Thanks
I read this thread and doesnt help.
It said that you can take rpm reading from IG from diagnostic box or from ecu but if you connect a volt meter to IG and Gnd what you read is the rpm?
I dont think so.
I think that this value who I read from IG I have to convert it with some mathematics to rpm.
That type I would like to know.

 

Yes, you need to decode/read the signal. While I don't know exactly what you need to do to accomplish your goal, it seems you can probably find what you need from using Google.

Since there are universal tachs which can all read the signal, there must be a standard.

Either way, that's where you'll pick up the signal.

 

If the volt who I read from IG is linear with rpm for example 700mv is 900rpm and 4volt is 9000 rpm then it is easy to write a programm to microcontroller to convert volts/rpm.
If it is not linear then it is a problem.

 

That seems like something very easy to test and confirm.