I'm certainly no kind of expert when it comes to electrical engineering, so any help is appreciated. For a project I'm working on I need some sort of small motor (smaller the better) to spin a wheel one revolution and then stop. I feel like the easiest way to do this would be to have a timed motor that starts at the press of a switch and then stops after a second or two, similar to the motor in an automatic soap dispenser. Is there an easy way of doing this? Thanks!

  • \$\begingroup\$ Uh I wanted to suggest a stepper motor but that would be too expensive and too large. \$\endgroup\$
    – Bradman175
    Jan 2, 2017 at 23:34
  • 1
    \$\begingroup\$ I think this question has a pure mechanical solution. \$\endgroup\$ Jan 2, 2017 at 23:45
  • \$\begingroup\$ How about a modified DVD tray motor with rack and pinion with end stop switches, minus the tray. \$\endgroup\$ Jan 2, 2017 at 23:47

1 Answer 1


If you need to reliably turn once, then a time function is not going to work - as conditions change (battery voltage, temperature, the slow buildup of gunkies in the mechanical components), the amount of time for "one rotation" will be greater or less than it was the day you built it.

You want to detect "the motor has completed its path" ... There are several techniques. One popular, cheap, and easy one: There are "photo-interrupter" modules (basically a block of epoxy with a small IR LED pointed at a small photo-diode or photo-transistor) that you can pass a notched disc through. When the notch is in front of the photo-diode, you get a signal that would tell your circuit "stop now, please".

A simple R-S flip-flop (built out of two sections of a NAND or NOR gate) and a transistor to control the motor current would complete the circuit. (one minor gotcha -- the 'begin turning' pulse must be shorter than the time it takes to make a rotation ... if you can't guarantee that, a second chip can solve that problem)

Sparkfun has a "kitlet" with a photo-interrupter ... https://www.sparkfun.com/products/9322


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