Building a digital tachometer

Thread Starter


Joined Apr 16, 2009
Hey people,

How do i build a digital tachometer using infrared transceiver and receiver to get an output of a varying voltage that feeds into an analog input of PIC? Do get back to me asap!



Joined Sep 9, 2010
You'll need what's known as a frequency-to-voltage converter. You can make one with a 555 timer circuit. You may need some signal conditioning to use the IR receiver to trigger the 555.
Last edited:


Joined Jul 17, 2007
I'm not certain why you'd want to go that route.

Instead, consider using a Hall-effect sensor near a gear or drilled hole or square/hex nut, backed up by a weak magnet. Hall-effect sensors are available in a wide variety of configurations. You'd want something like a single-phase switch, perhaps an AH337, or ATS137.

Then tie the sensor output to an I/O pin, and have it trigger an interrupt to increment a counter.

Have another counter keep track of the time. When this counter overflows, calculate what the frequency of the input from the Hall-effect sensor is, and from that determine the RPM.


Joined Sep 9, 2010
How do i build a digital tachometer ...?
Sarge is right. What's more important, making the tach or using the strategy you started with? If you want digital in the end, it's better to maintain the tach signal pulses as digital. No reason to convert to an analog voltage.