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.

I have one of those handhelds. There ok. If you can spare $70 a better option is an Eagle tree elogger V4. You get real time or data logging/graphs at 50hz sample rate for rpm, temp, amps/volts/watts and more. I mainly bought mine for rc aircraft but have used it more on non rc related things. Good bang for the buck

Bill, i’m confused here

Are you refering to this => https://www.amazon.com/MicroPower-V4-eLogger-Wire-Leads/dp/B0016KB9OO/ref=sr_1_1?ie=UTF8&qid=1541657542&sr=8-1&keywords=eagle+tree+logger+v4

assuming yes, how do you transform it into a not invasive RPM meter with a laser?

Yes. That’s what I’m referring to. It does require an optional rpm sensor. Either optical,
or the brushless type that connects to 2 of the 3 motor wires.
An example of how the optical sensor would work is by having a small silver colored or polished shaft collar mounted on the motor shaft with 180deg of the surface painted (or sharpie markered) black. The magnetic sensor would use 1 or more magnets mounted to the similar shaft collar example above. More magnets = higher resolution.