PIC 12F509 2009/08
There is a very smart design on micro-examples.com, I like it.
Here, I do some modifications, change the output pin to pin 5, reserve pin 6,7 for ICSP, and add a speaker.
The sensor coil is made by #23~#25 wire on 10~11 cm diameter, around 30 cycle, 450uH
The OSC frequency is around 1MHz, but no critical. you can use regular AM radio to detect the frequency.
Since this metal detector work by frequency shift, you have to move the detector side to side to detect an object.
For detail, Pls. visit micro-examples.comsee website or see the source code.
There is another smart, simple metal detector "A Simple BFO Metal Detector" from http://www3.telus.net/chemelec/Projects/BFO/BFO.htm
MD509 Hex & C source Code
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Philip Sun / TAIWAN