Dirt stupid "good enough" rpm meter



i would like to have a simple, good enough, easy to use, rpm meter.

i found the dt2234+ on banggood
it is a bit cheap ($12)

but it seems to do the job.

my typical usecase is that i have a spinning motor running at constant speed (hopefully)(typically turnigy), that i may control with odrive (and then i just want a quick and dirty way to check that it spins as i beleive it does). sometimes it’s with another controller (and here i dont have a clue). and sometimes it’s not even a brushless motor.

ideally i woudlnt connect anything mecanically. dont have to use/configure an oscilloscope.

i just want a second pair of eyes

what would you buy/make? how do u do this?


Last time I needed a tachometer but didn’t have one, I used a laser + LED (as crappy photo-diode) + oscilloscope.
I don’t think this is a good suggestion for your situation, but I just wanted to share ;D.