GB1476617A - Electric circuit arrangements - Google Patents

Abstract

1476617 Checking coins SODECO-SAIA AG 9 Jan 1976 [14 Jan 1975] 00834/76 Heading G4V An electric circuit arrangement for checking coins and the like comprising a digital sine wave generator 1 including a clock pulse generator 2, a shift register 3 and a resistive network 4, the output of the clock pulse generator being connected to the shift register and outputs of the shift register being connected to the resistive network, outputs of the shift register also being connected to a control circuit 6, to a first switch 7 and to a phase comparator 9; the output of resistive network 4 being connected to said control circuit 6, to said first switch 7 and to an L-C oscillatory circuit 5 formed by a primary coil and a capacitor; a secondary coil 11 inductively coupled to said primary coil and connected via a voltage comparator 10 to said phase comparator 9 and to a second switch 12; a low pass filter 14 connected to the output of said phase comparator; and means for evaluating signals developed in use in said arrangement and resulting from the passage of a metal object M between said primary and secondary coils. The control circuit includes a phase comparator and an integrator which in use supplies a D.C. control voltage to control the clock, pulse generator, the control voltage being proportional to the resonant frequency of the oscillatory circuit. The clock pulse generator is a voltage controlled oscillator and the phase comparator 9 is formed by either an exclusive OR gate or a flip-flop. Low pass filter 14 has an operational amplifier with a summation point to which a potentiometer is connected. The first and second switches are analog switches with controlled contacts, the switches having respective lowpass filters 8, 13, connected to their outputs. The oscillatory circuit is energized in use with its resonant frequency. The checking means described supplies four values in the form of voltages which can advantageously be used to approve or eliminate metal objects, particularly coins, in coin-collecting machines, coin operated telephones, vending machines and the like. The available values may be combined in various ways so as to ensure reliable approval or elimination.