Tachometer and frequency meter build in the same device

Thread Starter


Joined Aug 23, 2012
I am in need of tachometer and frequency meter build in the same device. For the tachometer I need
to measure a range up to 550000rpm- five hundred fifteen thousandths (dental hand piece).
I need to measure higher rpm. It is important that it starts from
150000rpm up. With the frequency meter I need to measure range up to 40 KHz.

I found this project on the internet and it has a incorporated frequency meter and tachometer

It looks like it is not a hard job to make it. I am not sure (I am a beginner in electronics) Does AT90S2313
need to be programed or not, because I did not find that it is written anywhere. If programing
is needed, where could I find the program. Has any of you done anything similar to this?
Which hall sensor would be best for this application?
Thank you in advance


Joined Jul 21, 2012
A tachometer & a frequency counter do very similar things.
A tacho reads out RPM(revs/minute),& a Frequency counter Hz(cycles/second),kHz,MHz,etc.

A car tacho normally looks at ignition pulses,counts them over a set period,applies a correction factor for the number of cylinders,either in calibration or in software.

A frequency counter could look at the same pulses(with an appropriate interface so you don't blow it up) & give a readout in Hz,etc.

You could then calculate the rotational speed in RPM,applying all necessary corrections.
The counter may do this in software,so that it becomes a frequency counter/tachometer.

Note,though,that spark ignition engines provide a convenient signal to count.

Electric,or pneumatic motors,do not,so the conventional ways to measure the speed of the devices are to either fit a sensor of some kind to the motor which will provide the necessary pulses,or use a stroboscope,which illuminates a mark on the rotating shaft.

The stroboscope is calibrated in RPM,& the rate of the light flashes is adjusted until the rotating part appears stationary.
The speed in RPM is then read off the stroboscope dial.


Joined Mar 31, 2012
Where is your signal coming from? I'm guessing that to achieve those kinds of speeds the device is air driven and has air bearings. The balance of everything is pretty critical, so you are going to have a hard time adding any kind of sensor or suitable marking.


Joined Feb 11, 2008
You can use any frequency meter, then to get RPM just multiply the freq reading in Hz by 60. That converts from events per second to events per minute.