There are a few methods of doing this but the simplest is to have a tuned
circuit ballanced by a certain capacitance. Proximity or contact from a
human being will change that capacitance, throwing the circuit out of
balance and trigger an event. A piece of wood will not do this because it is
an insulator. The circuit does not detect the difference between a piece of
wood and you, it just doesn't detect the wood at all.

"Joe Bemier" wrote in message
...
On Sat, 09 Sep 2006 03:22:18 GMT, "CW" wrote:

Capacitance change is the trigger. Likely somewhat more sophisticated but
essentially like a touch lamp.

I wondered about this as well. I read an article on the net that said
it senses a *change* between the wood and say a hand/finger. But what
if the accident happened before or after cutting. For example, and
illustrative purpose only, what if one was to stick their hand
directly into the blade? This would not result in a change of any
kind.
I don't know much about electronics.

Anybody?

"The Other Funk" wrote in message
news:a4pMg.54$rc3.28@trndny03...
I
thought that the trigger was a voltage spike. I'll get back to you.
Bob

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