piclist 1999\05\09\165944a >
Thread: Optical pickups and pics
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face BY : Mark Willis email (remove spam text)



Hi, Brian;  How about using a 24C01 or some such part, with a bunch of
protection?  Or a Dallas iButton with protection if needed?  (I haven't
looked at those yet, I know the postal service uses those for tracking
mail delivery persons' performance, so they must be pretty ESD safe, I
imagine.)

 Call me paranoid if you want, but if you mount a 24C00 in a PC board
soldered between a DB-09M connector's solder pot end, bring out Ground
on pins 1, 3, and 5, and to the outer shell, put Vcc on pins 6 and 9;
put SCL and SDA to pins 2 and 7, and 4 and 8, respectively (Multiple
redundancy here.)  Connect a 1N5231 5.1V Zener and/or something in an
SA5.0A transzorb across Vcc-Gnd, and maybe SCL-Gnd, and SDA-Gnd.  16
bytes should cover you, I'd think?  <G>  And they say 4kV ESD protection
on all pins, a little help should keep 'em pretty safe...  (Ground the
shell of the receiving socket through a 1M resistor, use that as a
static drain-off, then pin 1 or 5 should usually contact first, giving
you ground before Vcc; you can use pin 3 as a "poll back" pin with a
weak pull-up, in the receiving machine - when it's pulled low, you know
a 24C00's being inserted into the socket.)  Probably put a .1uF cap
across Vcc/Gnd on that PCB.  Might just SMD it all, it's a pretty rugged
IC.  And inexpensive, 40 cents or so.  In addition to the (2-10k)
pull-up's to Vcc on SCL and SDA, you could put small series resistors in
there to reduce peak current for ESD strikes, say 100R or so.

 In reality, if you drain the shell with that 1M resistor, and put 100
ohm resistors in series with SCL and SDA, plus maybe a 5.1V Zener & a
0.1uF cap across Vcc/Gnd, that's quite probably all you'll need (100
ohms both on the 24C00 side & attached to the input to the PIC on the
machine you're plugging it into <G>)  This may still be overkill <G>

 I like modules like this where it's hard to plug it in backwards, and
hard to kill it.  Working with "Joe Ten-thumbs" gets you designing
things that way.

 CF would also probably work, but I'd think this is cheaper by far (a
2Mb CF card runs about $15ish, and is harder to interface a PIC to.)

 Mark

Brian Gracia wrote:
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<3735F6FE.DA2F86DA@nwlink.com> 7bit

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