US 4,593,184 AGranted

Counterfeit detection circuit

AssigneeBrandt, Inc.

InventorsDavid Bryce, William Sherman, III

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Abstract

A magnetic sensor including a coil for sensing a changing magnetic field developed by paper currency moving past the magnetic sensor. A capacitor forms a tuned circuit with the magnetic sensor coil to pass only those signals lying within a predetermined frequency range. A comparator compares the signals lying within the pass band with a predetermined threshold to determine the presence or absence of genuine currency. The tuned circuit significantly improves the signal to noise ratio of the sensing means and hence, significantly improves the ability to determine the genuineness of the currency. In a second embodiment, the presence of a magnetic field having a field strength above the predetermined threshold is utilized to pass timing pulses for clocking a counter. A decoder gate coupled to the counter indicates the presence of a genuine bill, only after a predetermined count has been reached. A reset circuit is provided for resetting the detecting circuitry immediately after each bill is examined and before examination of the next bill.

Claims15

Dependent claims

Apparatus for detecting the presence of a genuine bill comprising:

magnetic sensor means including coil means positioned adjacent to the path of movement of a bill for generating a signal in the presence of a changing magnetic field created by the moving bill;
capacitance means forming a turned circuit with said coil means for passing signals within a predetermined band pass range in accordance with the impedance value of said coil and said capacitor;
means for amplifying the detected signal;
means for converting the detected signal to a DC level;
comparator means for comparing the converted signal against a predetermined threshold;
first storage means for storing the result of the comparison operation by said comparator means;
second storage means;
bill sensing means having a first output state as the bill is passing said magnetic sensing means and having a second output state when said bill has passed said magnetic sensor means;
said second storage means being responsive to the change of said bill sensing means to said second state for transferring the contents of said first storage means to said second storage means;
delay means responsive to the change of said bill sensing means from said first state to said second state for resetting said first bistable means a predetermined time interval after the contents of said first bistable means has been transferred to said second bistable means.

7 more elements

Dependencies are inferred from the claim text.