A company called Microswitch used to make these toroidal ferrite rings w/ a
slot in them.  They placed an analog Hall effect switch in the middle and
created a current sensor.  Now Honeywell has assimilated Microswitch and put
both analog and digital Hall effect sensors in the rings.  I used one years
ago, and it was great for my application.  Unfortunately, you will have to
power the Hall effect switch with a few mA of 5 or 12V power.  Sometimes
it's hard to beat a reed switch or loop of wires...

Check out the sensors at:

http://content.honeywell.com/sensing/prodinfo/current/

Tim

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Brendan Moran
Sent: Monday, May 03, 2004 1:21 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE:] Smartest binary way to detect current or no current
in a cable


Another way of doing this which may be more suitable for some situations is
to wind a coil on a toroidal core and pass one line of an AC source through
the centre of the core.

If you're trying to do it in DC, you're limited to resistors, current
mirrors or something I've been thinking of trying out: using hall effect
sensors as current detectors.

--Brendan

> I used to have a small device which had a line cord coming out one end
> and two outlets at the other end. I plugged my stereo turntable
> into one
> of the outlets, and my amplifier into the other. Whenever the
> turntablewas turning, the amp was on. When the turntable shut off
> at the end
> of the record, the amp turned off. Inside the box was a relay; its
> coil was
> connected in series with the turntable and its contacts powered
> the amp.
> The relay coil had a very low resistance; the relay may have been
> a low
> voltage (AC) type or it may have been specially designed for this
> device.
> John Power

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.