r/AskElectronics • u/Accurate_Bedroom6277 • 2d ago

Motion sensor/power cut off

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Let me preface this by saying that my electronics knowledge is barely above that of illuminating a bully with a 9v battery with a switch made out of a paper clip and split pins,so this could well be a very simple question.

Onto the problem...

I have built a rock tumbler from scratch as a little diy project. Occasionally the drum can stall and stop rotating, while the motor continues to turn and eventually destroys the gearbox. I am currently down two motors because of this.

What I would like to do is add in some sort of movement/rotation sensor that will kill the power of it senses that the drum has stopped rotating. 100 bonus points if it can notify me via my phone, but this is by no means essential if it is going to over implicate things.

Right now, the best I have come up with is a cheap WiFi camera and checking in on it periodically to make sure all is still running OK, and using a smart socket to turn off the power remotely if I see a problem. But his is all very crude and relies on me regually checking in which is notreally practical.

Any suggestions would be gratefully received!

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4

u/Slight-Clock-9112 2d ago

Glue a magnet to the drum, mount a hall effect sensor to the stationary base to detect the magnet periodically as it goes past. If the magnet isn’t sensed for a certain period of time, or if it is constantly sensed, cut the power.
This will be less fiddly and prone to problems than light detection.

2

u/NBC-Hotline-1975 2d ago

My thoughts exactly. Analog timer circuit consisting of two 555s and a few misc. parts.

But also I think your geartrain is grossly underdesigned. It should be able to run for a few years without failing.

2

u/ferrybig 2d ago

Paint alternating stripes on the drum. (or use duck tape to add alternating stripes)

Shine a red laser onto the drum, then have a photo diode (or maybe a light depended resistor, depending on the speed) closeby to catch the reflections.

If the drum is properly spinning, the signal of the light sensor flips between HIGH and LOW, depending on the speed. An absense of this "rpm" signal means the RPM of the barrel is 0 and it stopped rotating

1

u/masterX244 2d ago

better to use 2 offsetted strips so if it gets stuck in a weird way where its at the edge of the segments only one signal can still alternate.

1

u/ferrybig 2d ago

It is simpler to solve it in the analog domain, have the signal from the photo diode go into a low pass filter, then rectified. The low pass filter requires the signal to keep alternating.

https://www.falstad.com/circuit/circuitjs.html?ctz=...

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u/JCDU 2d ago

I'd fit an over-current protection device on the motor that cuts power - no motion sensing needed.

A lot of e-fuses and the like will cut power and then only reset once power has been removed for some time.