From: Spehro Pefhany
Subject: Re: Single Contact Touch Sensitive Switch
X-Newsreader: Forte Agent 1.92/32.572
Date: Sat, 04 Jan 2003 03:18:08 GMT
NNTP-Posting-Date: Fri, 03 Jan 2003 22:18:08 EST
On Sat, 4 Jan 2003 01:25:06 -0000, the renowned "Dan McDaid"
>Several years back I came across a circuit that was just that, a touch
>sensitive switch that was a single contact. I.E, it wasnt two contacts that
>were bridged by the skin on your finger, it was just one. At the time I was
>building a lamp as part of a school project - the idea was that to turn the
>lamp on and off, you only had to touch the base.
>Well, in the event I couldnt get this circuit to work, and since I didnt
>understand how it worked I was lost. I could find little on the subject and
>in the end gave up.
>I came across this earlier and it reminded me, its a similar kind of thing -
>except this works through glass and I think it is a different method to
>actually having an electrical contact.
>Ive seen this kind before where an electronic light switch was made - a
>blanking plate put in place of the light switch and on the back of the
>plastic plate was a square of foil.
>Can someone please explain to me how this works. I've always wondered and
>dont have a clue, I just dont see whats going on.
They (sort of) explain it- the circuit runs "hot" @ 240VAC 60Hz
relative to earth. Putting your hand near the foil sheet is like
putting a 240VAC signal with a few pF in series into the base of Q1,
which acts as a rectifier and amplifier. It depends on the hysteresis
in the relay operation to make it switch cleanly, there is no
"it's the network..." "The Journey is the reward"
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