Patent ID: 7490709

Claim:
A coin discriminating device, comprising a sensor electrode; an oscillator coupled to the sensor electrode, the oscillator being capable of generating an output signal with a frequency which is capacitively controllable; a capacitor for controlling the output signal, the capacitor comprising a first capacitor plate and a second capacitor plate for generating a capacitance therebetween, the first capacitor plate comprising the sensor electrode and the second capacitor plate comprising a coin positioned in a vicinity of the sensor electrode, the capacitor being free of a third capacitor plate coupled to the oscillator; a frequency detector for receiving the output signal from the oscillator as well as a reference signal from a reference oscillator so as to provide an output which comprises a difference between the output signal and the reference signal for detecting a frequency deviation in the oscillator output signal, caused by a variation in capacitance at the sensor electrode when the coin is positioned in a vicinity of the sensor electrode; and a processing device for determining a thickness of the coin from the frequency deviation, wherein the coin discriminating device is arranged such that the variation in capacitance occurs in a gap between the sensor electrode and a surface of the coin, wherein the size of the gap depends on the thickness of the coin.