www.circuitcellar.com did an article (i think last year) that measured the
amps on lines. it used a coil with a number wire wound a number of times
around the coil and one leg of the main passed through the coil. this
created a small ac signal proportional to the amps being drawn. they feed
this signal into an ADC but if all you need is on/off you could use a
comparitor.

michael

-----Original Message-----
From: Luis Fernandez <radiobit@DRAGONET.ES>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Thursday, April 23, 1998 2:01 PM
Subject: Detecting AC power line on/off


Hi list,

Would like to know your opinion in how to detect activity (power on) of
devices connected to mains power supply (220V 50Hz here) in order to provide
a clear input into a PIC I/O pin.

Goals are: Isolation from power line, Reliability, Low cost and low size

Relays with 240V AC coil are usually big because they are made to switch
heavy loads, so expensive and the coil can fail. The samallest I could find
was a 24V AC relay + resistor, but still not very reliable.

What about using a neon lamp and some kind of optical detector
(fototransistor) and may be an RC network to integrate the pulsing light of
the neon. What kind of optodetector can be used with this arrangement ?.
Any other idea ?




Luis Fernandez Cormenzana
RadioBit Sistemas, S.L.
    Sistemas de control de rondas
                         Patrol presence controllers
    Control de patrullas y vehmculos
                         Patrol vehicle fleet control
http://www.dragonet.es/users/radiobit
Tel/Fax: +34-96-5856457