Re: Induction sensor

Roger Dewhurst wrote:
"John Popelish" <jpopelish@xxxxxxxx> wrote in message
news:BM6dncOeet4FzbTbnZ2dnUVZ_uPinZ2d@xxxxxxxxxxxxxx
Joseph wrote:

Despite the small costs of the available units I'd still like to build
one
myself.

I have some pot cores and magnet wire for the coil, and uPs and relays
etc
for the logic and output. But...the oscillator and detection circuit is
new
to me and where I need some direction. I've googled and found some good
theory but very little on circuit specifics (except a 'hobby' metal
detector). Any help is appreciated.
I don't have a construction article for you, or even a
schematic, but I think you might get started by building a
Hartley Oscillator and sense the change in its DC supply
consumption as the sensed metal quenches its oscillation.
http://www.electronics-tutorials.com/oscillators/oscillator-basics.htm

How about an oscillator of which an induction coil is a component.

Sorry, I meant to say that, but must have assumed it was obvious. The oscillator inductor is the coil that produces a field in front of the sensor.

The
frequency changes when metal approaches the coil. An appropriate filter
lets through the changed frequency. The level of the signal is detected and
if high enough a buzzer sounds. Would that work?

The ones I have seen have the oscillator actually lose enough gain to stop oscillating, and the supply current takes a step (down, I assume). The logic output just detects the changes in the supply current to the oscillator.
.

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