Late at night, by candle light, oeguet@[EMAIL PROTECTED]
penned this immortal
opus:
>Hi Bob,
>
>my experimental measurement system has already a scope, spectrum
>analyzer, digital lock-in amplifier, signal generator and much more.
>
>So this experiment is a typical proof of concept which is saying: it
>is working!
>
>Basic operation of the laptop metal detector:
>Harmonic sine wave is sent through the earphone output. The impedance
>of the earphone output is round about 20 Ohms which delivers enough
>current for the transmitter coil. The transmitter coil has a capacitor
>connected defining a LC resonant tank. The transmitted frequency is
>the resonant frequency of the LC tank.
>The receive coil is in inductively balanced position (less coupled to
>transmitter coil) and has also a capacitor which also defines a LC
>resonant tank (same of transmitt frequency). The receive coil is
>inducing a small signal. The signal amplitude and phase will change
>upon a metal target nearby the search coil appears. The sound-card is
>used in full-duplex mode (while transmitting a signal, the receive
>signal is acquired).
>The digital lock-in amplifier (a two channel I & Q lock-in amplifier)
>detects the signal magnitude and phase of the receive coil. While the
>laptop knows the reference frequency (internally generated), it
>detects the changes by the receive coil.
>
>This is the most simple and sentive metal detector ever designed. You
>don't need any active electronics between the laptop and search coil.
>Search coil has only some capacitors and the inductors (transmit &
>receive coil). All the rest is done by the software using a high
>definition sound-card operated at 96 kHz sampling rate and 24 bit
>resolution.
>
>The experiment is showing amazing sensitivity results. It can compete
>with professional VLF detectors.
>Aziz
Why lug along a lap-top if the needed circuitry fits in a box the size
of a cigarette pack? All you need is a LED display and possibly a
beeper.
- YD.
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