Yo folks...

Long time no see... Been busy, and trying to hold on to job. Anyhow...
What I am looking for, and would like some input involves the best way to trigger a pin when the resistance becomes 500K or less Anything more than 500K, the pin remains open (I guess closed would be ok too, for I will be checking for a change in the bit, and turning on a motor).

I want the fewest parts possible. It doesn't have to be exactly 500K. I have about a 10% tolerance or so.

My thoughts and ideas are as follows:

1. Pull up resister on a pin...Since I can use a chip with a pull up resistor, I am thinking that it may be possible to use some kind of grounding resistor, and when that pin is shorted to ground with a 500K (or less) resister (in parallel , it will trigger the pin to fall).

2. Some kind of Ladder situation in which voltage could be measured and compared to a value.... 5 V being open, 2.5 volts being 500K, 0 volts being 500K or less. This could be done on a A/D converter or comparator of some kind, but this will involve more material. (Hey , if I can do it with just one resistor, I will <smile>)

I would prefer #1, but I have not set up anything to experiment with it yet. I was wondering if any of you had played with this kind of toy?


Dwayne