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Looking for circuit that can detect a nearby tuned circuit...

Hi Help please...

I need a circuit that can detect a nearby tuned circuit...

The object with the tuned circuit embedded within it is made to look like a rock

The 'rock' is dropped into a detection coil which will pick up the resonant frequency to identify the type of 'rock'

There will be three types of rock each with it's own resonant frequency.

I am an electronics engineer but I have little experience with RF.

I need a relatively simple circuit that can give me three logical outputs one for each rock type.

This is for an educational facility and I am not commercially involved.

Any help much appreciated.

--
Cheers
Graham Law
Reply to
Graham &/or Annie Law
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It all depends, as they say ... Checkout "Grid Dip Oscillator", or more probably these days "FET Dip Oscillator" for simple devices that respond to a tuned circuit.

Alternately, there are some 'electronic' pet doors that do exactly this - the cat wears a small resonant circuit and the door opens to it (on a good day).

Dave

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Reply to
Dave Garnett

Something like that used in the Schlage/Westinghous access card system should be just the ticket.

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John Miller
email domain: n4vu.com; username: jsm(@)
Reply to
John Miller 

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If you use three oscillators, each tuned to one of the three resonant
frequencies and connected to the detection coil through a suitable
filter (for isolation from each other) then when a "rock" is dropped
into the coil it will suck out power from the oscillator oscillating
at its (the rock's) resonant frequency.  Detect that suckout and
you're done!
Reply to
John Fields

You can use a single oscillator, if you have the time to characterise the circuit.

Make your rocks around 3 different masses of an inductive material. When you drop each rock through the 'detection coil' (which should be part of the tank on your oscillator), they will perturb the output frequency and amplitude, but each will perturb it differently.

For best detection, integrate the output of the oscillator and watch the signal amplitude (now as a DC signal).

This is the basis of certain electronic coin scanners.

Cheers

PeteS

Reply to
PeteS

Investigate those security labels they stick on expensive good in some stores. They are tuned circuits that are detected when they go through the checkout.

Reply to
CWatters

More..

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Reply to
CWatters

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