Creating one’s own metal detector is almost every school boy and college student’s dream project. Few get successful, while a few other come close but fail to complete the task, while there are a few more that get stumped in the beginning. The reason is simple, you need to follow the procedure very carefully and with complete confidence. We bring you a simple procedure here using which you can easily make your own metal detector without much hassle. It was a technique illustrated in Easy Treasure for a simple Beat Frequency Oscillator (BFO) metal detector. The system basically uses a pair of oscillators each of which is sufficient enough to produce a specific radio frequency. The first oscillator employs a coil of wire that is usually known as search loop while the second one uses a much smaller coil located in the control box and is termed as reference oscillator. The frequencies of these oscillators are adjusted in a manner that they come to an equal level and the small difference between then can be heard as a beat note. The beat note alters slightly as and when the search loop goes near any other metal piece.
On a normal mode, it is suggested to fix the frequency of search oscillator close to 100khz and the reference oscillator somewhere close to 100-250khz. This makes the range of beat note go from 250hz to 0 to 250hz. The beat note gets out of line completely as and when the pair of oscillators come to an equal level.
The detector becomes most sensitive as and when beat note comes close to 0, even a small change of 5hz will be noticed very widely.
To make this detector, the makers will need following parts:
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Power Source: Any kind of 9v battery PP3 is very suitable.
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Capacitors: 2 off 220uF 16v electrolytic, 5 off .01uF polyester, and 5 off .1uF polyester.
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Resistors: All resistors 1.4 watt 5%- 6 off 10k, 1 off 1K, 1 off 2.2m, and 2 off 39k.
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Transistors: All BC 184B or 2N2222A, or 2N3904. Any small frequency signal npn with a upper limit gain of 250 and more will work in this case. You can choose from almost a hundred options.
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Audio Output: It is recommended to use earpieces or headphones, in case, you are not able to get those you can always go for a 2.5” 8 ohms speaker.
The circuit can be built within a few hours once you have obtained all required materials. You can either use copper clad strip board for making the circuit board or use our own facilities for making one.

Coils: You can always start by carving three circles from a 3mm plywood, two with 16cm diameter and one with 15cm diameter. Sandwich the 15cm circle between the two others with wood glue. Once the glue is settled, wind 10 turns of an enameled .25mm copper wire near the groove at the border of the previous one. Once you are finished, connect the coils as shown in the schematic. There is one more method of doing this, but this is the simpler one.
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