data logging engine RPM with 10V logger

Resistors. 1k

That should work. However, you might want more isolation than that for other reasons.

So, another possibility would be to use an optoisolator chip, like this one:

which you can get here:

Use the chip like it describes in the test circuit in the datasheet.

Regards, Bob Monsen

wonderful, thanks.

Is the RPM reading an analog voltage? It seems that this value would be available as a frequency or pulse width.

Most automotive tachometer signals will be a pulse, either square wave or sine wave with the frequency per RPM depending on number of cylinders and whether two or four stroke (usually based on number of sparks per revolution). Diesels & outboard boat motors are another story

Hope this helps, Dennis

What I am going to do is build a frequescy to voltage conversion circuit using an LM2917. The circuit is simple and will output less than 10V. A nice voltage graph will be better than looking at RPM pulses to try to figure out the RPM.

Here is the spec on the LM2917:

thanks d1