About 2 years ago now I posted about some bumpers I made from an under-door seal:
Short version: The aluminum door seal mount is the ground, the rubber seal is the bumper, and has foam inside lined with foil, which hooks via a pull-up resistor to an input pin. When the bumper hits something the foil connects to ground, and we can read that we've hit something. This was working.
Since then another baby was born, things got put on hold, and are starting up again. The controller board has moved from an STK500 to one I've built, the bump switches now connect to a TI PCF8574 (i2c IO expander). And this aren't working so well.
So far I've had 2 PCF8574 chips stop working. One failed when, while testing the bumpers, my hand touched the aluminum holder (ie -ground). I'm now wondering if this was such a hot idea.
Can anything be done to make this safer? I had an idea to put diodes on the PCF8674 pins, so nothing can back-feed in (they can only go to ground). Is the danger of static discharge to the ring going to mess things up no matter what ?
-Chris