----- Original Message -----
From: "Alan B. Pearce" <A.B.Pearce@RL.AC.UK>
> >it's easy to tell that the LED leads are maybe a little
> >more magnetic than I'd like, but I think I can get away with it.
>
> I think you will find that many IC's, transistors, and other components
like
> LED's will have steel based lead frames in them. This is a consequence of
> having a material that matches the temperature coefficient of the
> encapsulating material.

Actually, you'd be surprised.  The most common culprits are diodes.  Most
transistors are fine.  We don't even use through-hole transistors now, as
they are too magnetic.  Capacitors, surprisingly, even electrolytics are
just fine:  almost completely non-magnetic.

> In the case of LED's you may be better off using surface mount examples,
and
> having a plastic "light pipe" to where you want the light if you cannot
> mount the led in a suitable place.

Well, that is a good idea, but the problem is that the LED's in question are
a pair of superbrights that are in a MS optical mouse. (I have tested, and
while the mice don't provide exact counts/mm they do produce repeatable
results.  For instance, on the 1 count/mm setting, the MS optical mouse I'm
usign produces roughly 2.16 counts/mm

> P.S. this sounds like super-conducting magnet territory :)

Believe it or not, that 0.35T field is comming from a permanent magnet (!!)
it weighs in at 17 metric tonnes of steel.  But NMRI is the game, and that
used to be exclusively superconducting, so you're on the right track ;)

----- Original Message -----
From: "Peter L. Peres" <plp@ACTCOM.CO.IL>
> I don't know about the 16F877 but most chip grids and part legs are made
> of mildly annealed iron which becomes magnetized quite easily plus may
> have some chrome plating in it that becomes even more so.

Well, my 16F877 only has just enough ferromagnetic material in it to just
barely hang onto one of the poles of the magnet (I just checked) so that's
not too big a problem.

> Also you will eventually have the Hall voltages in the semiconductor upset
> normal function. I'd say that the first to suffer will be the A/D and the
> voltage regulator (Hall voltage is directly proportional to current).

Now, this does worry me.  We do have a fair bit in the way of digital
electronics operating in the area near the magnet already, but we seem not
to have too much trouble with them dying.  The parts of the PIC currently in
use are: PORTB as digital I/O PORTA as digital in PORTE as digital inputs,
and the AUSART in synchronous mode.

> It would be interesting to know what you find ... please share it.

Once I have something interesting to tell you, I will ;)
Preliminary testing in the magnet should be today or tomorrow, though the
PIC's going to be at a bit of a distance until after that testing is done.

--Brendan

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