The Shop > Electronics & IC Programing

Hall Effect Sensor

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drmico60:
I used an optical sensor for my tachometer. I had already fitted a 60 hole index wheel to the spindle. I fitted an ir diode/photo transistor sensor salvaged from a defunct computer printer. One revolution of the index wheel then provided 60 pulses, so 1 rpm gives 60 pulses/minute or 1 per second. All that was needed was to add a cheap digital frequency meter to get a direct reading of rpm. More details are here:

http://mikesworkshop.weebly.com/tachometer.html

Mike

BaronJ:
Hi Mike,

I'll bet in that same printer there was either a long strip of plastic with index marks along its length and/or a plastic disc with index markings around its outer edge.  Both these devices work in exactly the same way as your tachometer, by producing pulses interrupting a light source.

Those printers are an excellent source of precision ground free machining steel bar.  Often there are one or more stepper or servo motors as well.  I've salvaged useful materials from several similar items usually given away free !

atunguyd:
I made a RPM counter for my mini lathe and used an optical sensor - much easier than a hall effect sensor.

Get yourself a photo transistor like this:
http://za.rs-online.com/web/p/reflective-optical-sensors/4889790/?origin=PSF_438298|fp&cm_sp=featureproducts-_-FeaturedProductsContent-_-4889790

Then if your spindle is shiney add a square piece of black insulation tape to it, or it is is black then add a square piece of aluminum tape to it.

Focus the photo transistor just above where the added tape rotates on the spindle and you have a circuit that gives one pulse per revolution.

I then fed this into a digital techometer from Hong Kong on ebay:
http://www.ebay.com/itm/0-56-LED-Display-Digital-Motor-Tachometer-Speed-Measure-Meter-panel-30-9999RPM-/190898639450?pt=LH_DefaultDomain_0&hash=item2c7272125a

And you have a digital tachometer.

To finish it off I added support for taking power from the mini lathes speed controller (so that tachometer switches on with the lathe) and mounted it all inside the mini lates control box so that it looks like a factory installation - if i remember when I get home I will post a picture.

Hall effect is a pain as you need to make sure your magnet stays in place, either gluing or drilling the spindle, also if you are going to use high revs then you need to balance your magnets so you end up with multiple pulsesetc...

vtsteam:
Too late for Norman, his works well now.

But a nice simple tach for reference.

Looks like these digital tachs are actually pretty universal, and can use Hall effect, NPN,PNP, dry contact and wet contact inputs, so Norman could have switched his sensor if he'd wanted. His came with the Hall sensor packaged for a little higher price.

Some of these on Ebay seem to include a connector with leads, some don't.

I ordered one to have on hand for projects.  Thanks for the note :thumbup:

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