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From: "Ken Taylor"
Subject: Re: HELP!!
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Tue, 8 Oct 2002 22:04:42 +1300
NNTP-Posting-Date: Tue, 08 Oct 2002 22:03:52 NZDT
"Groenewegen" wrote in message
> I need to design a cheap 'touch control' switch using basic logic devices.
> Touching the countacts with the users finger turns the output on/off,
> will stay on/off until the panel contacts are touched again.
> I have a CMOS Hex Inverter IC (74C14), an LSTTL J-K Flip flop (74LS76)
> a resistive divider.
> The output has to be used in conjuction with a visible LED.
Connect the panel to the input of the C14, with diodes to supplies for
protection. The 50Hz pick-up will be enough normally to work like that.
Rectify the output and have some capacitance for filtering, and use that to
clock the FF. If you're unsure whether the panel will reliably pick up like
that you could have a trace connected to the circuit ground going around the
edge with the bulk of the panel as the pickup inside this. Or if you don't
like 50Hz pick-up at all do a panel with a whole series of concentric
circles (or squares - make it pretty if you like) closely spaced so that
wherever you touch on the panel your skin resistance takes the input of the
gate high/low and use that to clock the FF.
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