AM Radio Metal Detector.

[techstar]

I am looking to build a good AM radio metal detector, if good is possible that is. Any projects any where ?.

[waltr]

I would not consider this good but a simple demonstration of a BFO MD.
But lots of info on the web on how to make one of these.

[Tim]

There are thousands. Try this one from Talking Electronics with windings and (1n) caps adjusted to around 100 kHz. From distant memory I went 30 turns .25mm, 150mm coil, 22 or 47 nf caps replacing the 1n's., with a ten turn 100R pot seriesed on the + input for fine tuning. Best beat was around 1000 on the AM tuner.

[kt315]

http://www.geotech1.com/cgi-bin/page...obox/index.dat

[kt315]

http://www.geotech1.com/forums/showt...11150-2-boxxxx-)

[techstar]

Thanks tim I will try your recommended circuit. What maximum in ground depth would you expect on say a medium sized coin, would 3 inches be too much to expect.

[homefire]

Some can do better then your expecting. 5-6 inches in ground that's not so hot.

[Tim]

As homefire says. But you do need good audio to hear the change in tone. Also it might be worth trying a H-bridge oscillator (for extra sensitivity) or centre tapped coil design (to negate mineral effect).

[techstar]

Thank you for the advice.