Change pulse to constant voltage

Thread Starter


Joined Jan 11, 2007
Hi, thanks for all help in advance. Much appreciated.

For my project i need to convert a pulse (coming from an rpm sensor) to a constant output voltage, which needs to be between 0 an 6 volts (the output voltage is the input for a control circuit, controlling the speed of a fan).

The pulse will constantly change between 500 pulses per min and 7000 pulses per min. The output voltage will need to change in relation to the pulse rate, as a cirtain pulse rate will need to result in a cirtain output voltage.

To complicate matters, i need the ability to alter what level of voltage is given out per speed of pulse, ie the ability to control what output voltage is reached at the max of 7000 pulses per min.

Any ideas how such a circuit may be built ?

Again thanks for taking the time to read this and thanks for all help given :)


Joined Apr 20, 2004

It might be a lot easier if you used a microcontroller to count the pulses and do the controlling. Otherwise, you can probably rectify the pulses (may need to amplify the first) and filter them to DC with a capacitor. You may need to have a resistive path to pull current off the cap to give you the voltage proportional to speed. Tailoring op amp gains might give you the level of control over the output voltage you want, but digital will be better.


Joined Jun 30, 2006
An idea you'll have to work up to do what you want. Use the pulses to turn on a circuit that then applies DC to a capacitor. The circuit can be a transistor, multivibrator etc. The more pulses per second the higher the output voltage. You will need to do a bit of testing and work to make that scale between 0-6 volts. If that 0-6 volts is meant to actually drive something you might need to feed that voltage to something like a three terminal adjustable regulator and let the regulator handle the load.