Hobby motor sized tachometer

[KeithSeeley]

Mech guy here who's out of his element

Looking to build a very inexpensive tachometer with small LCD display for a project using hobby sized motors (think R/C motors or smaller). I'm guessing I need either a mini inductive pickup or opto device wired into an LCD but I have no idea where to start looking. I deal with machine control systems (plc's and the like), so basic electrical I'm OK with. It's this small scale component stuff that I'm very uncomfortable with.

Total cost target is roughly $20. Is this something that's doable with off the shelf stuff? Any guidance would be appreciated.

 

[ScottyUK]

Have a look at slotted opto-switches. One of them in conjunction with a slotted disc and a little bit of electronics would give you a pulse train proportional to shaft speed.


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If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

As Scotty says.

For really low power consumption, you can also experiment with a little magnet glued to shaft end (if possible) plus a pick-up coil. That will not work at low speeds but OK above a few hundred RPM.

There are LCD units with built-in counters. One is available at

http://www.pongrance.com/ddfc-cc.html

and there are lots of others.

If your need is one off and you don't mind the looks, you can use a DMM with frequency range. The three dollar units do not seem to have frequency. But add a few dollars and you should get what you need.

If you need 1000+ units, you should have someone make them for you by your specification.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

I built a tach for a printing press. $1.99 for a toy DC motor that made a good tach generator. Then a voltmeter and a couple of scaling resistors to calibrate the meter in appropriate units.
After proof of concept with the $1.99 motor, we upgraded to a $14.00 motor that had better bearings for longer expected life.

Bill
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"Why not the best?"
Jimmy Carter

 

[Compositepro]

I was going to suggest the dc motor/tach generator with LCD volt meter. You might also look at bicycle speedometers. They now use a magnet and pick-up on the wheel, have an LCD, and you can program the calibration.

 

[MiketheEngineer]

Seems to me Radio Shack used to sell one - like less than $20. Try their website

 

[fsmyth]

If you can find an old 5 1/4" floppy drive, the
motor and the electronics are all there. Good
for up to about 10 kHz, IIRC. Been a while.
<als>

 

[KeithSeeley]

Thanks for all the suggestions. I will look into them, but the dc motor as tach seems like a good fit.