DIY or Buy a Tachometer?
GreatScott! shows how to make your own RPM meter that works better than an inexpensive purchased model.
“DIY or buy” is a question creators must ask themselves all the time. Usually it’s a matter of purchasing something that simply works, versus spending your time to make something that eventually works, may still take some tinkering. In the case of this homemade tachometer by GreatScott, however, he was able to build a device that works much better than a unit acquired online, at a lower price!
The process starts out with testing the purchased tachometer, which has a decent build quality, and several interesting features. Unfortunately, optical measurements taken with it didn’t agree with the roller interface on the same unit, and after some analysis, neither actually gave a correct reading. He then hooked up an inexpensive IR sensor — which measures a reflected beam to indicate object presence — to an oscilloscope. This produced excellent results, and upon analyzing the circuit, he went to work creating an all-in-one tachometer setup.
GreatScott's DIY tach is controlled by an Arduino Pro Mini, and features a simple on/off interface. A small OLED display outputs the RPM, and can also show a “SLOW” message to indicate that the source needs to be sped up. A LiPo battery and charging circuitry is added to make it portable, and everything is arranged on a cut perfboard base.
More details and code are available in the project's write-up. GreatScott notes that DIY is the clear winner here, though if you were able to spend a bit more money on the buy version things might be a bit different!