| 摘要 |
<p>A switch for operation by a finger F at a side of a glass plate (106) remote from the switch has an infra red emitting diode (104) and a phototransistor (107), which are mounted close to each other and the glass plate. A moulding (109) prevents transmission directly from the diode to the phototransistor whereby circuitry provided can detect presence of the finger according to whether the finger reflects transmission from the diode to the phototransistor or not. In one embodiment, the circuitry includes means (115) for sampling and holding the received signal, means (117) for amplifying it by a certain percentage and means (116) for comparing the held amplified signal with the non-amplified signal.</p> |
