Q: circuit suggestions for a contact sensing circuit.

Too vague to give any meaningful suggestions.

So this will probably turn into one of those long threads where everyone offers a solution for what they think the problem might be.

This sounds like one of those threads that may attract unnecessary sarcastic replies to a reasonable question. But let me try to make the problem statement more clear.

I have two pieces of metal, tightly clamped together and need to be able to sense if they begin to separate. I need to sense the very small separations on the order of .005". This situation is such that proximity sensors won't work because of physical and other constraints and strain gage type sensing of contact related strain would drain a battery powered system over a long period of time.

I suspect that this problem has been solved before and I assumed that this might be a reasonable forum to ask about it. I actually have an idea in mind that would involve fashioning a switch in which and isolated region of two contacting surfaces could act as a switch but this would be too difficult to explain using only text.

If anyone knows of any types of contact sensing circuits I would welcome any input and will determine if the suggestion is adaptable to my situation.

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Uuue touchy, let me be the first to come up with a solution to one of a wide range of problems covered by your description.

I suggest you take a strip of white paper and clamp half of it between your two pieces of metal. Look at the protruding half with an optical sensor as it goes past due to the rotation of your two peices of metal.

When your two peices of metal separate the paper will fall out and you will stop sensing it. The sensor is not rotating so you don't need a radio link or battery supply.

Wouldn't it be easier cure the problem and fix them together better rather than try and detect failure?

Perhaps look into remote sensing strain gauges. This works as follows... You tighten up the joint. Fix the guage across the gap and zero the output. When the joint moves the load is transferred (in partl) to the guage which reports this typicalyl as a change in resistance (but there are lots of types).

More...

Radio for remote strain gauge/load cell outputs...