Lights do not always need to be on at full power. Often it would be useful to be able to turn off the more powerful lights to achieve softer illumination, but this requires an installation with two separately-switch-able circuits, which is not always available. . . Energy-Saving Switch Circuit Image If the effort of chasing out channels and replastering for a complete new circuit is too much, then this circuit might help. Normal operation of the light switch gives gentle illumination (LA1). For more light, simply turn the switch off and then immediately (within 1 s) on again. The circuit returns to the gentle light set-ting when switched off for more than 3 s. There is no need to replace the light switch with a dual version: simply insert this circuit between switch and lamp. . Energy-Saving Switch Circuit Diagram Parts List: Resistors: R1 = 100Ω R2 = 680Ω Capacitor: C1 = 4700µF 25 V Semiconductors: D1,D2 = 1N4001 Miscellaneous: K1,K2,K3 = 2-way PCB terminal block, lead pitch 7.5 mm F1 = fuse, 4AT (time lag) with PCB mount holder TR1 = mains transformer, 12V @ 1.5 VA, short-circuit proof, PCB mount B1 = B80C1400, round case (80V piv, 1.4A) RE1 = power relay, 12V, 2 x c/o, PCB mount RE2 = miniature relay, 12V, 2 x c/o, PCB moun How does it work? Almost immediately after switch-on, fast-acting miniature relay RE2 pulls in, since it is connected directly after the bridge rectifier. Its nor-mallyclosed contact then isolates RE1 from the supply, and thus current flows to LA1 via RE1’s normally-closed con-tact. RE1 does not have time to pull in as it is a power relay and thus relatively slow. Its response is also slowed down by the time constant of R1 and C1. If the current through the light switch is briefly interrupted, RE2 drops out immediately. There is enough energy stored in C1 to activate RE1, which then holds itself pulled in via a second, normally-open, contact. If current starts to flow again through the light switch within 1s, LA2 will light. To switch LA1 back on it is necessary to turn the light switch off for more than 3 s, so that C1 can discharge via R2 and RE1. The printed circuit board can be built into a well insulating plastic enclosure or be incorporated into a light fitting if there is sufficient space. . PCB-Layout Caution: the printed circuit board is connected directly to the mains-powered lighting circuit. Every precaution must be taken to prevent touching any component or tracks, which carry dangerous voltages. The circuit must be built into a well insulated ABS plastic enclosure.
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