Abstract: In a coin detection system, a coin passes between conductive plates which form a capacitor, which provides part of the frequency controlling capacitance of an LC tuned oscillator circuit. The presence of a coin between the conductive plates alters the capacitance, and consequently alters the output frequency of the oscillator circuit. The oscillator output is supplied to the clock of a counter, optionally following frequency division in a frequency divider. The counter counts the number of clock pulses received in a 10 ms period, and the count value is provided to a microprocessor via a shift register. The count value will be a measure of the frequency of the output of the oscillator. The microprocessor uses the output to determine whether a valid coin has been received, and if so, what the denomination of the valid coin is.