Subject: Re: Single Contact Touch Sensitive Switch
Organization: Nobody nowhere
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
Date: Sat, 4 Jan 2003 02:28:50 -0000
NNTP-Posting-Date: Sat, 04 Jan 2003 02:29:03 GMT
"Dan McDaid" wrote in message
> 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
> were bridged by the skin on your finger, it was just one. At the time I
> building a lamp as part of a school project - the idea was that to turn
> 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
> in the end gave up.
> I came across this earlier and it reminded me, its a similar kind of
> 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.
It works on mains-hum pickup. Like when you touch or get your finger close
to a high impedance input of a amplifier you get a big hum out of the
loudspeakers. This circuit is just a high gain, high impedance amplifier
that takes that hum signal, smooths it and turns the relay on.