How to force a floating pin (tri state?)
August 5, 2011
I am well on my way to making a fancy logic probe from a LCDuino. Just to fill in, I started with making a probe from a TL082 dual op-amp which works quite well. I assumed that making the same thing out of a microprocessor would be a peice of cake but man, this whole binary/digital thing is sorta getting me. I think I may be trying to make a (what is it?) tri-state thingie...
Basically, I have a simple, one-wire probe. When it is touching something high the micro sees a high and prints a corresponding message on the LCD. If it is low, a message is printed on the LCD for that as well. As it stands now, "floating" is seen as a low. I would like it to be seen as "nothing".
The question is, how does a micro tell if something is simply "not connected"? Not high, not low but floating? I thought about doing this through an ADC but quickly came to the realization that I had no idea how this route would help me. Then I thought about pull-ups and pull-downs and again, stuck. Right now, the only thing I can figure is to connect the guts of my logic probe to the micro and let the op-amp do the "floating" business for me.
I am REALLY open to thoughts on this one. I think I need a real-life circuit-nerd (EE).