| 摘要 |
<p>Automatically timed lights 9 for entrances and stairways in a mains circuit are selectively actuated by switches (4, Figs. 1,3) fed by transformer 10 and rectifier 11 to operate at very low voltage and small current. In conditions of low natural illumination, closure of one of the switches causes integrated circuit 15 to deliver a pulse of duration determined by potentiometer 16 to an isolation device 7 containing an optical coupler and a zero passage voltage control whereby the pulse is delivered to triac 8 which switches on the lighting network while the switching assembly is isolated from the mains voltage by transformer 10 and device 7. When natural illumination is above a level set by potentiometer 27, a photoresistor 25 acting through transistor 26 inhibits the action of integrated circuit 15. <IMAGE></p> |
