Hi,
Out of curiosity - how do those hand held AC proximity sensors work ? (e.g. the pen sized devices that you hold near to a live mains wire which light up when AC is present). Is there an off the shelf IC that you can purchase to make one yourself ? Anyone have a circuit diagram for one ?
Reason for asking, I want to build an electronic circuit to detect the presence of 240v in a wire - without disturbing the wire.
Many thanks, Tim.
Electrostatic charges are on the surface of the wire. Those simple probes you're thinking about are just hi-z input sensing circuits via a couple of diodes to rectify charge on the surface so it can drive a CMOS or FET type sensing circuit. Normally input load are tailored to work in the desired range and maybe a clamping protection diode to save the day. Electricity produces charges on the surface of the conducting material. If you would like a PDF file on the subject of how electricity flows? I think I may have something designed for students. You can email me if you wish.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
The simplest form of that uses an NE-2 neon glow bulb. They don't work very well, but they don't need any batteries. It just uses the AC electrostatic field and the fact that you are providing the connection on the other side of the bulb.
The modern ones use a little bit of electronics. You don't need much. Just a high input impedance and enough output current to drive the LED. There is no need to rectify and level detect or anything like that. The amplified 60Hz is basically applied to the LED directly.
If it wasn't for the ESD problem, this circuit would work:
D1 470R C1 !!-----!
-- Many thanks, Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com Please visit my GURU\'s LAIR web site at http://www.tinaja.com
Calling that circuit "basically a 60Hz e-field radio receiver" is kind of an insult to all the Real Radios out there, Don. :-)
Very simple, they use CMOS logic where the first (inverting) gate is biased in the linear region with a high value feedback resistor. That makes the input sensitive to small signals that get amplified by that gate; the output is then passed to the second stage which amplifies it more and saturates (signal swings from ground to supply voltage). That signal swingcan be detected by another gate, which can drive an LED. I have seen three variations of this, and one of them had an adjustable sensitivity.
Your battery symbol is upside-down.
Yeah, I've always thought that it should be the opposite, since the can on carbon-zinc batteries is the (-), but that's the standard..
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
So, then, Don's symbol is "right" in that the thick black one, the carbon, is plus, and the thin line, the zinc envelope, is minus.
That's the way I've _always_ done it, and I don't care if everybody else in the world does it wrong. ;-)
Cheers! Rich
:-)
As long as you label the side _you_ designate as + it won't be misunderstood, even if you do it *right*. :-)
Ed
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