🚀 go-pugleaf

In article <1993Jan2.104609.4196@arizona.edu> dparker@ece.arizona.edu (Douglas R. Parker) writes:
>Greetings.
>
>Quite a while back I attempted to repair the tape deck
>in my Toyota. I found that one of the plastic shafts that
>rotates the casette's tape wheel had cracked, leaving a gap
>in the gear teeth. I assume the reason for malfunction and
>subsequent devouring of many a tape was a perpetual End of
>Tape being recieved. I tried using similar salvage parts to
>replace the gear but this didn't work. The reason for this,
>I think, is that the original gear had a small disk magnet
>fixed to its base, and beneath it was a small surface mount
>component. I assume this is some sort of a tape speed
>regulation. My question? The matter is rather academic at this
>point, as this was a good excuse to buy a CD unit. However,
>I am still very curious as to how the thing worked. Although
>my EMAG is rusty, I would guess that a rotating B field was
>somehow used to induce current in this sensor, which was
>then used as a feedback. Does anyone out there have experience
>with this type of arrangement?
>Just extremely curious,
>
>dparker@helios.ece.arizona.edu
>
> 

Good chance that it is (was) simply a Hall effect sensor.  A micro in the
deck used the square wave from the sensor to control the speed.

I don't pretend to know the physics behind it, but a Hall effect sensor is,
in effect, a magnet-controlled switch.  Hysteresis makes the output kind of
"spongy", though.