| 摘要 |
<p>A light unit (1) contains several light-emitting diodes (2, 3, 4) supplied from a low current source via a terminal (5). A light receiver (7) contains several phototransistors (8, 9, 10) in series with a load resistor (11) and supplied from a voltage source via a terminal (12). The phototransistors form a NAND gate. The output stage is a high gain amplifier (19) whose output is connected via a capacitor (20) to the inverting input of a comparator (21). The non-inverting input is supplied with a variable threshold voltage by a potentiometer (22). When one of the phototransistors is shaded from its light source by the object (6), the comparator output changes state instanteneously.</p> |
