Frequency to voltage conversion

Thread Starter


Joined Jan 5, 2013
Hi all,

I am working on a project where I am driving LEDs based on the RPM of an engine.

It isn't the typical method where you just listen to the ignition events of a coil, rather, it is coming from a standalone ECU that outputs 0-12V square wave (frequency depends on RPM).

I know I can use the LM2917 to do this conversion, however, I am not able to simulate it in Multisim. I tried looking up the circuit diagram for that chip, but I don't know how I would immitate a "charge pump".

In any case, I hope someone has some insight into my options or has a solution.



Thread Starter


Joined Jan 5, 2013
You can breadboard the LM2917 circuit per the app. notes without simulating it...
I am not sure what you mean. But if you are saying that I should test it on the board without simulating it in the program first, then I don't really like that option because I want to be able to show this design on paper.


Joined Aug 21, 2008
If you would rather not use the LM2917, you can get the same functionality, though with lower linearity by merely triggering a monostable multivibrator with the signal from the ignition coil, then low-pass the output of the monostable.

To obtain good linearity, pulses out of the monostable should be a couple tens of percent of the shortest period (at the highest RPM) that the circuit would encounter.


Joined Sep 9, 2010
I built one of those, a 555 frequency to voltage meter. It was in the Forrest Mims booklet on the 555. It worked quite well. I fed it tones from my guitar tuner and the output voltage was quite linear in that range.


Joined Oct 18, 2012
The LM331 can be fun as a frequency to voltage converter and only requires a few capacitors and resistors to function.