|
(11) | EP 0 300 782 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Coin discriminator |
| (57) A coin (1) is tested for its thickness by bouncing a wave packet of ultrasound off
the surface (1′) of the coin, and timing the arrival of an identifiable element (7)
of the reflected wave packet at a sound receiver (Rx). A zero-crossing point (7) of
the reflected wave packet is used as the element, and is detected by converting the
output (B) of the receiver (Rx) into a rectangular waveform (C) by using a comparator
(8), and then using a microcomputer (10) with a timing function to time a particular
edge of the rectangular wave. A flip-flop (11) is armed by an arm signal (D) from
the microcomputer to await receipt of that pulse edge, and the time of clearing of
the flip-flop is measured by the microcomputer to determine the coin thickness. Measurements are also periodically made with no coin present of the position of the coin support surface (2) to take account of any change in position of the transmitter (Tx) and receiver (Rx). |