Hall Effect Sensor

[NormanV]

I wish to fit a tachometer to the milling machine that I am building, I have bought one but the sensor is too large to fit in the available space. I have almost no knowledge of electronics, could anyone suggest a smaller replacement for the sensor that I have, it measures 62mm long x 12mm dia. The diameter is not the problem, it is the length.
Here is the data from the sensor that I have.
Thanks, Norman

[John Rudd]

Norman,
I got some Hall effect sensors from EBay.......
Already mounted on a pcb with connections ready to wire up to tacho....around a couple of quid iirc....
Only thing is they come from afar if you can wait?

http://www.ebay.co.uk/itm/Hall-Sensor-Module-for-Magnetic-Field-Detecting-0-15V-/320748421434?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item4aae18813a


http://www.ebay.co.uk/itm/Hall-Entry-Sensor-Module-for-Magnetic-Field-Detecting-0-15V-DC-/181192549703?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2a2feae547        ,
Even cheaper.....

[NormanV]

Hi John, thank you for your speedy reply.
This is the sensor that I have.
It is completely enclosed, and safe from debris. I was hoping that there might exist a similar product but in a smaller package.
Norman

[Chuck in E. TN]

You can use a hall effect transistor, about the size of a pencil eraser, and enclose the leads and the sensor itself in heat shrink tubing. Should be available at your local electronics shop.
The hall effect uses a small magnet to trigger it. I used one for the pickup on my X2 mill.
Chuck

[John Rudd]

Chuck,
Trouble is here in blighty that we don't have shops like you that side of the pond....so he'd struggle...

I suggested the little module to save him the aggro...
His choice......

[BaronJ]

Hello Norman,

what you have there is an "Inductive Proximity Sensor".  You can get them as small as 6 mm diameter and 20 mm long.  As far as "Hall devices" are concerned RS Components will sell you one over the counter or by post.  They are not very expensive !  The last time I bought some they were much less than £1.00p.   Now if you want to play around and salvage some, any computer case cooling fan will have at least one and usually two in it.  An old floppy drive motor will have upto four in there.

You should also be aware that there are several types of hall devices.  Some are simple sensors that will give you a variable output that depends upon the magnetic field strength, others are switches that will give a digital output, positive or negative going depending upon how they are wired and the magnetic polarity.  Some of the switch ones require one magnetic pole to turn them on and the opposite pole to turn them off.

HTH.

[micktoon]

Hi Norman , as Baron said RS Components will sell what you need but its not too easy finding what you want at times when buying there. Another option you could look into is I have used the same type sensor as yours on my lathe but have also used a sensor from what I remember that was exactly the same but much smaller say 6mm diameter and 30mm long on a kit car speedo, I got mine from a place called Green Gauges that I think no longer exsist but if you google kit car speedo sensors you might find easy place to get one from without all the tech spec being needed ?

  Cheers Mick

[NormanV]

Hi Mick, I've searched Ebay but can only find sensors in moulded plastic housings for £30 or more. I've given up the idea of a neat assembly and will mount the sensor that I have, it will just have to stick out!
Thanks everyone for your help.
Norman

[hopefuldave]

I just spent a tenner.on eBay.for a 'gear tooth sensor' chip which comes with a built-in Nd magnet and supposedly works up to 5kHz, which works out to roughly 4000 rpm on my lathe, a bit faster than I need... It takes 5 - 24. Volts dc in and produces nice neat square waves, compensating for sensor gap etc. Much easier than making it up as I go along!
The chip is an ATS667, to me it looks ideal....

[BaronJ]

There are other ways Norman could go...

Optical !  Using a reflective surface or broken beam.  Very cheap and very easy to implement.
Again if you know where to look, lots of salvageable parts sent to landfill.

 

[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