AW: AW: [basicstamps] URGENT PLEASE HELP/done

Archiver

Hi Mike,

how would I be protecting the stamp against static discharge? Why is it
necessary? I have a 1.5 Ohm resistor between the user and the stamp, would
that do?

Thanks for warning me,

Uli

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Urspr

Archiver

>how would I be protecting the stamp against static discharge? Why is it
>necessary? I have a 1.5 Ohm resistor between the user and the stamp, would
>that do?

Uli,

Where an I/O pin is looking directly at the outside world, you should
anticipate repeated static discharges of several KV from a capacitance
equivalent to a few hundred pF (human body model).

I'm no expert on ESD protection, but I suspect you need at least one series
resistor from the touch pad, a transient suppression diode to ground, and
then another series resistor to the Stamp I/O pin. The second resistor
protects Stamp input protection diodes, because the voltage across a 5V TVS
diode actually goes way beyond 5V during an ESD event! Each resistor should
be a few K ohms. The first resistor will arc internally if it's hit with
several KV, so you might need a spark gap at the touch pad as well.

I'm sure you're thinking, by now, that all of this protection stuff is
going to cost more than a switch. Good thinking...

Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!

Archiver

I was thinking there was a touchpad one-shot example in the 555 cookbook.
This might be a safer interface.

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Original Message

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I can't sleep since I read your mail... ;-) My circuit is still running but
maybe you are right in what you expect it to do. Is there an easier way to
connect touchpads to a stamp? Are their ready ones? Doesnot even have to be
cheap because the customer pays...

Any suggestions welcome, thank you.

Have a nice day and pray for peace, uli