warning lamp with Euro lights

[Phil Payne]

> You are correct that a steady magnetic field surrounds a wire carrying a
> steady electric current.  But what is required for that magnetic field to
> drive a current in a secondary wire is for that wire to cut through the
> magnetic field or, alternatively, for the magnetic field to cut through
the
> secondary wire.  The first is what the alternator of your car does.  A
coil
> of wire is turned within a magnetic field generating an alternating
> current.  The second is what a transformer does.

You could build a steady state detector using a Hall sensor.  A friend in
England has a 'clamp-around' probe for his multimeter that is effectively
both - it will indicate a DC component in an AC flow and vice versa.  Useful
device.

There's so much ripple and general electrical filth in most auto circuits
that you'd probably pick up a signal in the circuit proposed.  Wouldn't be
very reliable, though.

--
  Phil Payne
  http://www.isham-research.com
  +44 7785 302 803
  +49 173 6242039