Sensing AC voltage by non-contact means.

Fit clamp diodes to Vdd and GND on the relevant pin plus a current limiting resistor in series with the sensor.

Graham

What accuracy did you have in mind ?

Rene

I assumed he meant on - off. A cmos gate based sensor won't do better than that for sure !

Graham

You already have. The pen-shaped things do exactly what the CMOS circuit does -- sense the electric fields around the conductors, which propagate through the insulation just as well as magnetic fields from current do. You don't need current flow.

So, attach a CMOS inverter to an insulated wire, which you'll then place next to the AC input. DON'T LEAVE THE INPUT WIRE BARE -- the circuit depends on capacitive coupling through the insulation. It should sense any voltage through the insulation. You should get a 60Hz (50Hz?) square wave out. Rectify the ouput of the input inverter, send the rectified voltage to a second gate, attach an LED to the output of the second gate, and you have a mains voltage sensor. I doubt that you really need to protect the sensing input -- very little energy can get through the insulation.

Note that this is not a measurement tool, it is a sensing tool. Measurement depends on too many things to attempt it through two layers of insulation. It may also be too sensitive, so you may have to try some added grounding resistors (multimegohm, probably) to the sensing input.

Note also that the pen gadgets are intended for internal unshielded wiring. At least where I live, the power company has individual conductors anchored to the house up high, then a shielded 2-conductor cable carrying the mains supply down to the meter. This circuit (or one of the pens) is unlikely to work through the cable shield. But it'll work fine on individual, insulated wires.

John Perry

For what purpose- to locate the cable or verify voltage presence.

Makes no sense, it is only a cb away from being an interior cable.

"David Collier"

** Stick a fine sewing needle through the insulation.

You can use any convenient AC voltmeter then.

........ Phil

"David Collier"

** Seems most unlikely there is ever zero current flow in a *live* conductor feeding a main fuse box.

Nor any current whatever in a *dead* one.

So, in the absence of any need to get a voltage reading, a sensitive current clamp will do for a live/dead descriminator .

.......... Phil

In article , David Collier wrote: [...]

This is not a "standard circuit". It is a "substandard circuit". It will detect the AC or perhaps the static build up in your clothes until the CMOS gate gets zapped.

Those things that use a Neon bulb are most likely what you really want. They will tell you that there is AC voltage there.

If you want to actually measure the voltage, that's another matter all together. You can measure AC voltages with a fair accuracy without making electrical contact. The design of such things in not a prject for the beginner because it involves mains voltage.

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kensmith@rahul.net   forging knowledge

If it is an incoming cable,it should have a steel wire mantle(in my house it has),so any voltage will be shielded from you,and you may measure anything between zero and full voltage.

2 diodes take care of that.

they wont work with no contact

I doubt that stopped many folk on this ng

NT

I'd give that answer an A*

I am simply looking for a go/no-go so I can call out the right engineer, ( off a list of 3 ). It all saves money, and improves time - to - resume

- service. I've got 8 hours of back-up battery to get it fixed, and I can't afford to call out all 3 engineers in succession, apart from the cost. This lot could be 50 miles from the nearest house, let alone depot.

My only point is that I'd like to be able to BUY one of these things, rather than make one. Why can't I ( pout ).

I am hoping that I can access the live tail just where it enters the board fuse - I appreciate it will be well shielded all the way to there, but I'm hoping the shielding stops short enough for my purposes.

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

DONG - wrong answer.

We have

board fuse ( may trip ) meter ( may go faulty , though unlikely ) first consumer unit ( may trip ) second consumer unit ( may trip )

I'm not allowed to connect to the wires before the exit from the 1st consumer unit, ( safety rules ), but I must diagnose any of the above faults, as most of them need to call out a different engineer :-( David Collier

email can be sent to Dexdyne.com , under name from_usenet@

Agreed, which is why I'd like to buy it in with the bugs taken out. I'll pot the thing or stick it in a biro tube or something, which should avoid too much risk of static....

Gadzooks, a new idea. Do we really reckon a neon bulb with one end free will detect electricity from a mains cable enough to light up? I could make an opto-coupler up with it, and that would be really sexy, and, as you say, actually robust and safe.

ain't a beginner :-)

and anyway I have no intention of going inside the cable insulation, that's the whole point!

but I don't want to measure, just detect presence.

TVM.

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

"David Collier"

** My comments are fine.

YOU failed to explain your wacky application !!!!

** Then you need to sense ALL the cables concerned to see if they are live.

NOT just the incoming supply as you FALSELY posted !!!

" I need to detect live voltage in a mains cable, from outside the cable, without electrical contact. The cable is the one INTO the main fusebox, so no toucheee. "

......... Phil

What is it about Aussies that makes them so easy to start an argument with?

actually no....

** Seems most unlikely there is ever zero current flow in a *live* conductor feeding a main fuse box.

I have a consumer unit with a single cct breaker running a single load. Either the RCD, or the cct breaker can trip, and give me zero current each side of the board fuse, while it's all still live.

Even in a domestic situation tripping the RCD would contradict you.

But let's not start a flame war about it.

Thanks for caring enough to answer!

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

"David Collier"

** What is it that makes pommy pricks into such pig arrogant cunts ??

All bastard sons of trollops and vile pommy bitches - I suppose.

** Was a " main fusebox " in your OP.

Be a f****ng pink elephant next.

** Shame how several major household appliances are *NOT* fed from an CD - plus all the lighting circuits etc ** Never need to throw flames at a complete FOOL who would not know if his arse was on fire.

Like it is right now.

** Drop dead.

......... Phil

[snip]

Fortunately Phil is NOT your typical Aussie. I've found the Australians to be marvelously friendly people (Phil and Bill excepted ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
     It\'s what you learn, after you know it all, that counts.

Oh crud, they are cheap and easy to find in Los Angeles and any other city where there are established IBEW locals. I have one. I bet i can find another. If you really want one, send your address to joseph_barrett "at" sbcglobal.net I will even send you a copy of the receipt.

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JosephKK