a coin box monitoring circuit for use in pay telephones , providing coin detection , coin volume totalization , and full coin box signaling to the telephone central office . an included coin chute assembly has three channels that cause nickels , dimes , and quarters to pass through specific locations within each channel . light sources and light detectors detect the passage of coins . a microprocessor is utilized to control the light sources , monitor the detectors , and volumetrically count the coins passing through the coin chute . on reaching a full condition , a microprocessor then controls a relay to signal that the predetermined coin box level has been reached .