Halogen light switch

The switch circuit, intended for low-voltage halogen lights, extended the life of the lamps, because it ensures that the filament current is increased gradually, thus obviating the high peak currents that flow through the lamp with normal switches, The addition of a timer would enable the circuit to switch the lamp off again after a[…]

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General purpose timer

The timer is intended to actuate an apparatus for a predetermined period of time, for instance, an ultraviolet exposure unit or a photographic enlarger. Periods may be set between 0.1 s and 999.9 s. The periods are set with the due aid of thumbwheel switches and stored in four Type 74HCT190 counters, IC4-IC7. The setting[…]

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House telephone

Telephones are now readily and cheaply available: two identical ones and a handful of components enable a simple house telephone to be set up. Since the two telephones are connected in series as shown in the diagram, half the supply voltage exists across either of them. Neither buzzer will sound since the potential across zener[…]

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