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Carl invited me to "drop by the Tech forum sometime and let folks know what's going on". I have four metal detector designs either published or scheduled for publication during this year. Here is some information:
* MATCHLESS METAL LOCATOR. I just had an i.b. metal detector published in Silicon Chip magazine (June 2002). Its active components are a 7556 dual timer i.c. and a BC549 transistor - thirteen components in all, plus the two coils, an on/off switch, and battery. It operates at around 1kHz. One half of the 7556 serves as the transmitter. The BC549 serves as Rx preamplifier, and this feeds the other half of the 7556, wired as a high performance sine-square convertor. The output of the convertor goes straight to the headphones. A Victorian penny seems as good a standard as any (31mm or 1ΒΌ" diameter) - it will pick one up clearly at 150mm. The trade-off for such simplicity, however, is some drift.
* B.F.O. METAL LOCATOR. I have a small b.f.o. metal detector scheduled for publication in Silicon Chip magazine (June 2002, I think). This has a 4093 Schmitt NAND i.c. at its core, with NAND reference and search oscillators. Their frequencies are mixed by a third NAND gate, with the fourth gate providing amplification for headphones. It employs eight components, plus the coil and battery. It operates at around 80kHz. It has good stability and easy tuning, and will pick up a Victorian penny at 70mm.
* EPE BOUNTY (working title). I have an i.b. metal detector scheduled for publication in EPE magazine October 2002. This uses two gates of a 40106 Schmitt hex inverter to set up the alternating magnetic field in the Tx coil. The Rx coil is coupled to a sensitive 072 preamplifier, which incorporates hysteresis, thus returning the signal to a square wave. The signal is then fed to a third gate of the 40106, which is wired as a peak detector. The transmitter operates at around 1kHz, and with the 40106 output being virtually rail-to-rail, output volume is good. Stability is good. This design will pick up a Victorian penny clearly at 200mm, maximum 240mm.
* LITTLE BIG B.F.O. DETECTOR (working title). I have another b.f.o. metal detector approved in concept for EPE magazine. This is at the moment under development. It has a single 40106 Schmitt hex inverter i.c. at its core, incorporating reference and search oscillators. It uses about a dozen components. The frequencies of the two oscillators are mixed using signal diodes. Then I take a spare 40106 gate, and use this to give the reference oscillator a wobble. This reduces the problem of frequency lock, and gives a Geiger-like click-click in the headphones to indicate accurate tuning. It operates at around 80kHz. It will pick up a Victorian penny at 80 to 90mm. Since it gives either a clear signal or none at all, its sensitivity is effectively higher than similar quoted figures.
With kind regards,
Rev. Thomas Scarborough,
in Cape Town.
E-mail [email protected]
* MATCHLESS METAL LOCATOR. I just had an i.b. metal detector published in Silicon Chip magazine (June 2002). Its active components are a 7556 dual timer i.c. and a BC549 transistor - thirteen components in all, plus the two coils, an on/off switch, and battery. It operates at around 1kHz. One half of the 7556 serves as the transmitter. The BC549 serves as Rx preamplifier, and this feeds the other half of the 7556, wired as a high performance sine-square convertor. The output of the convertor goes straight to the headphones. A Victorian penny seems as good a standard as any (31mm or 1ΒΌ" diameter) - it will pick one up clearly at 150mm. The trade-off for such simplicity, however, is some drift.
* B.F.O. METAL LOCATOR. I have a small b.f.o. metal detector scheduled for publication in Silicon Chip magazine (June 2002, I think). This has a 4093 Schmitt NAND i.c. at its core, with NAND reference and search oscillators. Their frequencies are mixed by a third NAND gate, with the fourth gate providing amplification for headphones. It employs eight components, plus the coil and battery. It operates at around 80kHz. It has good stability and easy tuning, and will pick up a Victorian penny at 70mm.
* EPE BOUNTY (working title). I have an i.b. metal detector scheduled for publication in EPE magazine October 2002. This uses two gates of a 40106 Schmitt hex inverter to set up the alternating magnetic field in the Tx coil. The Rx coil is coupled to a sensitive 072 preamplifier, which incorporates hysteresis, thus returning the signal to a square wave. The signal is then fed to a third gate of the 40106, which is wired as a peak detector. The transmitter operates at around 1kHz, and with the 40106 output being virtually rail-to-rail, output volume is good. Stability is good. This design will pick up a Victorian penny clearly at 200mm, maximum 240mm.
* LITTLE BIG B.F.O. DETECTOR (working title). I have another b.f.o. metal detector approved in concept for EPE magazine. This is at the moment under development. It has a single 40106 Schmitt hex inverter i.c. at its core, incorporating reference and search oscillators. It uses about a dozen components. The frequencies of the two oscillators are mixed using signal diodes. Then I take a spare 40106 gate, and use this to give the reference oscillator a wobble. This reduces the problem of frequency lock, and gives a Geiger-like click-click in the headphones to indicate accurate tuning. It operates at around 80kHz. It will pick up a Victorian penny at 80 to 90mm. Since it gives either a clear signal or none at all, its sensitivity is effectively higher than similar quoted figures.
With kind regards,
Rev. Thomas Scarborough,
in Cape Town.
E-mail [email protected]