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PICList Thread
'Interfacing to ac powerlines'
1997\12\08@065856 by Abdul Gaffaar Hoosain

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Hi all!

I need to do some simple interfacing to 220V powerlines.
A PIC16C84 must monitor eight different lights to determine if they
are switched on or not. All the switches are situated together, so if
I could find a way to "tap" the powerlines, and feed this to the PIC,
I don't hafta lay km's of wire to the lights themselves (this won't
be practical anywaty). I'm a little nervous about connecting mains to
the PIC. Also, I hafta keep the component count really low, mainly
for budget-, and space-related reasons.

Anyone have some simple suggestions that could help me?

Thanx!
Gaffs.

1997\12\08@093759 by Reginald Neale

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>Hi all!
>
>I need to do some simple interfacing to 220V powerlines.
>A PIC16C84 must monitor eight different lights to determine if they
>are switched on or not. All the switches are situated together, so if
>I could find a way to "tap" the powerlines, and feed this to the PIC,
>I don't hafta lay km's of wire to the lights themselves (this won't
>be practical anywaty). I'm a little nervous about connecting mains to
>the PIC. Also, I hafta keep the component count really low, mainly
>for budget-, and space-related reasons.
>
>Anyone have some simple suggestions that could help me?
>
>Thanx!
>Gaffs.

It is possible to sense the voltage directly. Use a couple of high-value
(several meg) resistors in series to a PIC input. Senses only the positive
half-cycle, of course; the internal diode clips the negative one. However,
there are safety issues here; doubtless you know about the potentially
fatal danger of having your logic circuitry share a common with the power
line. One safe way is to use a special optocoupler that HP makes for
providing a logic output from a power-line input.

Also, monitoring the switched voltage doesn't tell if you if a lamp has
burned out. Can you steal a few milliamperes from the lamp current to feed
the optocoupler? That would be more fail-safe.

If the lamp current is high enough, it might be possible to use a clamp-on
inductive sensor to sense lamp current and provide isolation at the same
time, but that's probably a more expensive approach.

Reg Neale

1997\12\08@120520 by Rob

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Hi,

I like to use the Hewlett Packard HCPL3700 AC/DC to Logic level
Optocoupler for high voltage interface.  They go for around 4 US dollars
each.

Rob


On Mon, 8 Dec 1997, Abdul Gaffaar Hoosain wrote:

{Quote hidden}

1997\12\08@141629 by steve

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Reginald Neale wrote:
>
> >Hi all!
> >
> >I need to do some simple interfacing to 220V powerlines.
> >A PIC16C84 must monitor eight different lights to determine if they
> >are switched on or not. All the switches are situated together, so if
> >I could find a way to "tap" the powerlines, and feed this to the PIC,
> >I don't hafta lay km's of wire to the lights themselves (this won't
> >be practical anywaty). I'm a little nervous about connecting mains to
> >the PIC. Also, I hafta keep the component count really low, mainly
> >for budget-, and space-related reasons.
> >
> >Anyone have some simple suggestions that could help me?
> >
> >Thanx!
> >Gaffs.

Hall effect current sensors could work well here. You would also be
isolated from the mains power.


Steve Collins

Petron Industries Inc.
Houston, Texas

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1997\12\08@153055 by Andrew Mayo

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Well, the low-tech solution is two ferrite toroids. Wind around 8 turns
of light-duty but mains-rated wire for the primary - this is in series
with the bulb, of course, and 16 or so turns of normal hookup wire as
the secondary. Assuming a 100W lightbulb you have around 0.5A per bulb
flowing which gives you plenty of current in the toroid. The secondary
voltage will probably be a volt or so - feed this to a comparator of
some sort - IC or a couple of transistors, depending on your preferences
and supply voltages etc, and there you are. Fully isolated and very
cheap. Also won't blow up if the light bulb shorts out.

{Quote hidden}

1997\12\08@155337 by Gary T. Pepper

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At 12:50 PM 12/8/97 GMT+0200, you wrote:
>Hi all!
>
>I need to do some simple interfacing to 220V powerlines.
>A PIC16C84 must monitor eight different lights to determine if they
>are switched on or not. All the switches are situated together, so if
>I could find a way to "tap" the powerlines, and feed this to the PIC,
>I don't hafta lay km's of wire to the lights themselves (this won't
>be practical anywaty). I'm a little nervous about connecting mains to
>the PIC. Also, I hafta keep the component count really low, mainly
>for budget-, and space-related reasons.
>
>Anyone have some simple suggestions that could help me?
>
>Thanx!
>Gaffs.
>
>

Another possible solution is to use a phototransistor,
cadmium sulfide photoresistor, photodiode or other light sentive device to
'stare' at each lightbulb (easy to do, even in the presence of ambient light).
Convert that to a logic level and you've got a photon based light monitor.
This is the same idea principle as in an optocoupler!  :)

Gary Pepper
e-mail: gpepperspamKILLspamcapitalnet.com

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