hi,

Can anybody tell me where to find hall effect switch from junk electronic appliances. I cant find it in supply stores in my place.

thanks, boyabs

 

You can find them in most floppy drives, VCR's also use them - sometimes as reel sensors, but if not the capstan and drum motors (DC brushless motors) usually have three each.

 

Hi Nigel,

thats interesting,
i didn't know they were there.
could you elaborate on that a bit,
so that i could recognise them,

Cheers, John

 

To use a VCR capstan motor as an example, if you remove one from a VCR there is a large flywheel on the bottom, and the capstan sticking up through a bearing at the top.

They are usually held together simply by a circlip on the capstan at the top side of the lower bearing. Remove the circlip and pull the flywheel downwards, sliding the capstan out of the bearings - it takes a little force, as the flywheel is a magnet and trys to hold on.

Once that's out of the way there's a PCB underneath, with individual 'piles' of driver coils around the outside. Also on the PCB are a number (usually 3 or so) hall effect devices - they look like tiny black transistors, but with more wires.

These motors are known as 'DC brushless motors', a conventional brushes motor uses the brushes to switch different coils in to circuit to give rotation - in these motors the coils are switched by transistors, but the circuit needs someway of knowing whereabouts the rotor is to switch the coils at the correct time - that's what the hall effect sensors do.

 

You can also canibalized a bipolar hall-sensor from damaged PC-fan.
The bipolar hall is very interesting thing: with magnet nord-pole switch on, and south-pole switch off.

 

Hi nigel,

Thanks a lot for your info. on where to get hall effect switch from
junk floppy disc driver. I found three inside, but my problem is, it has four legs. I dont know where to connect the +,ground, and out wires which are common on three legged hall effect i.c.


boyabs

 

Have a look at http://www.cybench.co.uk/salv/hall/hall2.htm, which might help you, although it only shows three pin ones. Try following the circuit on the old drive to see what goes where.

 

Hope this helps, I managed to find a circuit diagram for an old Hitachi VCR capstan motor - it shows the three 4 pin hall effect sensors. It looks like the outputs require feeding into a differential amplifier.

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