This might sound a daft idea but it works.

A bridge rectifier in series with the lamp (Ac,Ac) and a led (opto and
resistor, across the +/- in parellel with a 5v zener and a small cap)
basicly when there is lamp that's on the led is also on on the opto the cap
just makes the signal 0 or 1 instead of a square wave princable is
extendable to large lamps by the size of the bridge. Make sure that the
semis can handle the cold current of the lamp its about 10 times the running
current for the first cycle. Should be cheeper that a ct and amplifier.

Just my 2p

Steve 

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Tim ODriscoll
Sent: 15 December 2005 17:00
To: Microcontroller discussion list - Public.
Subject: Re: [EE:] Detecting a blown lamp

Hi Everyone,

I've found a toroidal current sense pcb-mounted device for a little over one
UK pound. Excellent. It says it's suitable for 50Hz AC voltage and 1A to
10A. It's basically a rectangle with a hole in the middle for the
current-carrying cable, and two pins underneath it for the output.

The datasheet states that there is 50 ohms resistance between the two pins
and the graph implies that I should see 4mV to 5mV for 1A and 7.5mv for 2A.

That means I should be able to detect what kind of bulb is in the light too,
right? Cool. The two possible bulbs are 250W and 500W, and I live in the UK,
so it's 230vAC.

I've never used the A/D port on a pic before, but I've got a 16f628
earmarked for this, which has one I believe.

How does one connect up this current-sensing coil to a pic a/d pin then?
I'm assuming something nice and simple like I ground one end of the coil and
just wire the other directly into the a/d port, then it's all software?

Or would that not yield any input?

Cheers,

Tim.

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