On Tue, 23 Sep 1997 14:22:29 -0700 ERIC SCHLAEPFER writes: > Hi All, > > Does anyone here know a really good static control method that >works > with the PIC16F84? I have six I/O lines that go outside of the > project's case and go through really long wires to switches. Some >of > the wires are exposed and will be fiddled with by people, and I >don't > want the chip damaged. I've checked the Microchip application >notes, > and they say to put at 10000 pf capacitor from power to ground. >Is > this all that is necessary? For input only lines I'd recommend resistors (100K to 1M) in series with the inputs and placed near the chip. The internal pull-ups can't be used then, add pullup resistors on the "outside" end of the isolation resistors. For real heavy-duty protection split the resistors in two and put a zener, MOV, or similar device between the midpoint and ground. Also be sure the resistors have adequate voltage capacity so they won't flash over internally. Stay away from physically small resistors like 1/8W or SMD ones. Small capacitors on the PIC pins to ground would further attenuate static spikes that may couple capacitively through the resistors. > > I thought of putting in a TTL buffer or an optoisolator, but the >data > lines need to bidirectional. Bidirectional lines are tougher to isolate. A series resistor may still be tolerable if the loading is light. For example if its a matrix scan, make the pullup resistors rather large and add some delay so the long RC times can settle.