Does anyone know how this TL082 opamp-based circuit works?

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Elektronman

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This is a dollar tester circuit, it is used to distinguish fake notes from the real ones. The magnetic ink present in US dollar is detected through a magnetic head (like those used in tapes audio recorders). and a LED lights up if the note is real
Does anyone know how this work in practice?
Here there is a picture of the device:
https://www.smartkit.net/start.php?d_B_1101_E_Dollar_Tester.php

I've posted the schematics here:




Thank you
 

TL081 is dual OPA. Magnetic head is connected to the first OPA which is noninverting and has gain about 470. Second OPA is Schmitt triger connected to the output of the first one. Head has to be pulled over certain part of note. Induced voltage in magnetic head is amplified and trigers Schmitt stage which lights LED. Pot is used to set working point of circuit (sensitivity).
 

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