Patent ID: 7537099

Claim:
A method of operating a coin discriminator by measuring how a metal coin affects a coil means when the coin is subjected to magnetic fields generated by the coil means external to the coin, and wherein eddy currents induced in the coin are detected by detection means external to the coin, the method comprising: inducing a magnetic field in the coil means forming part of a resonant circuit of the coin discriminator by driving the coil means by time varying signals produced by an oscillator circuit, the oscillator circuit comprising a voltage controlled oscillator and a phase selector which feeds, in sequence, two phase-shifted outputs from the oscillator to drive the coil means, measuring eddy currents in the coin induced by the magnetic field of the coil means, wherein the eddy currents are measured at two frequencies that are determined by causing the oscillator circuit to lock, in sequence, with the two phase-shifted outputs from the oscillator, and comparing the determined frequencies with predetermined values of frequency for different types of coins for determining a type of the coin.