Counterfeit coin detector circuit

• US 4,846,332 A
• Filed: 02/29/1988
• Issued: 07/11/1989
• Est. Priority Date: 02/29/1988
• Status: Expired due to Fees

• Current Assignee: Cubic Toll Systems, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Automatic Toll Systems Incorporated
• Inventors: Quinlan, Thomas
• Primary Examiner(s): Bartuska, F. J.
• Application Number:
  US07/162,190
• Time in Patent Office: 498 Days
• Field of Search: 194/317, 194/318, 194/319
• US Class Current: 194/317
• CPC Class Codes: G07D 5/02 Testing the dimensions, e.g. thickness, diameter; Testing the deformation
• CPC Class Codes: G07D 5/08 Testing the magnetic or electric properties

Abstract

A counterfeit coin detector circuit comprising an constant frequency and voltage maxima and minima square wave oscillator input to a tank circuit including an inductive probe and an adjustable capacitance. The tank circuit is driven at a fixed and stable frequency and has a variable peak to peak AC output voltage amplitude which is a function of the characteristics of the coin under test. The AC output of the tank circuit is converted to a DC voltage correlated to the peak to peak AC ouput from the tank circuit. A group of window detector circuits are employed to determine whether the DC voltage output falls within certain preset ranges corresponding to the presence of particular coins. The presence or absence of a window detect can be used to accept or reject the coin or to otherwise take appropriate action with respect to the coin under test. The circuit is capable of being retrofitted into standard toll booth coin collecting systems and provides a simple and very rugged circuit for detecting counterfeit coins or slugs which is also very temperature stable.

Claims

1. A coin testing circuit comprising:

means for generating a square wave voltage of substantially constant frequency and amplitude, said means having an output;

a resistor having an output and an input, said input being operatively connected to the output of said means for generating a square wave voltage;

a probe tank circuit including a capacitor and an inductor connected in parallel to each other, said inductor being positioned in magnetic field relationship with a coin to be tested, said probe tank circuit having a first operative connection to the output of said resistor and a second operative connection to ground and generating an oscillatory output voltage at said first operative connection having a frequency equal to the frequency of said square wave and a peak to peak voltage amplitude which is a function of the characteristics of the coin under test;

means for generating a direct current voltage output correlated in value to the peak to peak amplitude of the voltage, said means being directly connected at the first operative connection of said probe tank circuit to the output of said resistor; and

means for determining whether said direct current voltage output has a value less than a first predetermined voltage value and greater than a second predetermined voltage value at a particular time.

2. A coin testing circuit comprising:

means for generating a square wave voltage of substantially constant frequency and amplitude, said means including a clock oscillator, a binary divider, an amplifier and a voltage reference of substantially constant value, said clock oscillator having a voltage output of substantially constant frequency, said binary divider having an input operatively connected to the output of said clock oscillator and having a digital output of a substantially constant frequency which is a fraction of the frequency output of said clock oscillator, said amplifier having a first input operatively connected to the output of said binary divider, a second input operatively connected to the voltage reference, an output, and means for generating a voltage at said output having a substantially constant value in relation to the value of said voltage reference when a digital input is present at said first input;

a resistor having an output and an input, said input being operatively connected to the ouput of said amplifier;

a probe tank circuit including a capacitor and an inductor connected in parallel to each other, said inductor being positioned in magnetic field relationship with a coin to be tested, said probe tank circuit having an operative connection to the output of said resistor and having an oscillatory output voltage frequency equal to the frequency of the output of said binary divider and a peak to peak voltage which is a function of the characteristics of the coin under test;

means for generating a direct current voltage output correlated in value to the peak to peak amplitude of the voltage at the operative connection of said probe tank circuit to the output of said resistor; and

means for determining whether said direct current voltage output has a value less than a first predetermined voltage value and greater than a second predetermined voltage value.

3. A coin testing circuit comprising:

means for generating a square wave voltage of substantially constant frequency and amplitude, said means having an output;

a resistor having an output and an input, said input being operatively connected to the output of said means for generating a square wave voltage;

a probe tank circuit including a capacitor and an inductor connected in parallel to each other, said inductor being positioned in magnetic field relationship with a coin to be tested, said probe tank circuit having an operative connection to the output of said resistor and having an oscillatory output voltage frequency equal to the frequency of said square wave input and a peak to peak voltage which is a function of the characteristics of the coin under test;

a charge-coupled precision DC rectifier having an input operatively connected to the operative connection of said probe tank circuit to the output of said resistor, said charge-coupled precision DC rectifier having an direct current output corresponding in value to the value of the peak to peak amplitude of the voltage at said input of said charge-coupled precision DC rectifier; and

means for determining whether said direct current voltage output has a value less than a first predetermined voltage value and greater than a second predetermined voltage value.

4. A coin testing circuit comprising:

means for generating a square wave voltage of substantially constant frequency and amplitude, said means having an output;

a resistor having an output and an input, said input being operatively connected to the output of said means for generating a square wave voltage;

a probe tank circuit including a capacitor and an inductor connected in parallel to each other, said inductor being positioned in magnetic field relationship with a coin to be tested, said probe tank circuit having a first operative connection to the output of said resistor a second operative connection to ground, said first operative connection having an oscillatory output voltage frequency equal to the frequency of said square wave input and a peak to peak voltage which is a function of the characteristics of the coin under test;

means for generating a direct current voltage output correlated in value to the peak to peak amplitude of the voltage, said means being directly connected at the first operative connection of said probe tank circuit to the output of said resistor; and

window detection means for determining whether said direct current voltage output has a value less than a first predetermined voltage value and greater than a second predetermined voltage value at a given instant of time, said means including a high threshold voltage comparator, a low threshold voltage comparator, a first voltage reference having an output of substantially constant value equal to said first predetermined voltage value, and a second voltage reference having an output of substantially constant value equal to said second predetermined voltage value;

said high threshold voltage comparator having a first input, said first input including means operatively connected to the operative connection of said probe circuit and to said output of said resistor, a second input operatively connected to the output of said first voltage reference, an output and means for generating a signal at said output when said first input is less than said second input;

said low threshold voltage comparator having a first input, said first input including means operatively connected to the operative connection of said probe circuit and to said output of said resistor, a second input operatively connected to the output of said second voltage reference, an output and means for generating a signal at said output when said first input is greater than said second input;

means for periodically generating a clock signal operatively connected to said high threshold voltage comparator and said low threshold voltage comparator; and

means for determining whether an output signal is simultaneously present on both said high threshold voltage comparator and said low threshold voltage comparator during presence of said clock signal

5. A coin testing circuit comprising:

means for generating a square wave voltage of substantially constant frequency and amplitude, said means having an output;

a resistor having an output and an input, said input being operatively connected to the output of said means for generating a square wave voltage;

a probe tank circuit including a capacitor and an inductor connected in parallel to each other, said inductor being positioned in magnetic field relationship with a coin to be tested, said probe tank circuit having a first operative connection to the output of said resistor and a second operative connection to ground, said first operative connection having an oscillatory output voltage frequency equal to the frequency of said square wave input and a peak to peak voltage which is a function of the characteristics of the coin under test;

means for generating a direct current voltage output correlated in value to the peak to peak amplitude of the voltage, said means being directly connected at the first operative connection of said probe tank circuit to the output of said resistor;

window detection means for determining whether said direct current voltage output has a value less than a first predetermined voltage value and greater than a second predetermined voltage value at a given instant of time, said means including a high threshold voltage comparator, a low threshold voltage comparator, a first voltage reference having an output of substantially constant value equal to said first predetermined voltage value, and a second voltage reference having an output of substantially constant value equal to said second predetermined voltage value;

said high threshold voltage comparator having a voltage follower amplifier having an input operatively connected to the output of said means for generating a direct current output, said voltage follower amplifier having an output, a comparator having a first input operatively connected to the output of said voltage follower amplifier and a second input operatively connected to the output of said first voltage reference, an output and means for generating a signal at said output when said first input is less than said second input;

said low threshold voltage comparator having a voltage follower amplifier having an input operatively connected to the output of said means for generating a direct current output, said voltage follower amplifier having an output, a comparator having a first input operatively connected to the output of said voltage follower amplifier, a second input operatively connected to the output of said second voltage reference, an output and means for generating a signal at said output when said first input is greater than said second input;

means for periodically generating a clock signal operatively connected to said high threshold voltage comparator and said low threshold voltage comparator; and

means for determining whether an output signal is simultaneously present on both said high threshold voltage comparator and said low threshold voltage comparator during presence of said clock signal.

6. A coin testing circuit comprising:

means for generating a square wave voltage of substantially constant frequency and amplitude, said means having an output;

a resistor having an output and an input, said input being operatively connected to the output of said means for generating a square wave voltage;

a probe tank circuit including a capacitor and an inductor connected in parallel to each other, said inductor being positioned in magnetic field relationship with a coin to be tested, said probe tank circuit having a first operative connection to the output of said resistor and a second operative connection to ground, said first operative connection having an oscillatory output voltage frequency equal to the frequency of said square wave input and a peak to peak voltage amplitude which is a function of the characteristics of the coin under test;

means for generating a direct current voltage output correlated in value to the peak to peak amplitude of the voltage, said means being directly connected at the first operative connection of said probe tank circuit to the output of said resistor;

first means for determining whether said direct current voltage output has a value less than a first predetermined voltage value and greater than a second predetermined voltage value at a particular time; and

second means for determining whether said direct current voltage output has a value less than a third predetermined voltage value and greater than a fourth predetermined voltage value at said particular time.