battery supply timer

— t--- —22 • 104 • C1 • in For those in doubt the "try it and see" method may take longer but will work just as well. If required, the two darlingtons can be substituted by discrete transistors. battery supply timer A need often arises for battery powered equipment to be switched off after a certain period of time. Although timing circuits are legion, it is not such a simple matter to switch a power supply some hours of use. The circuit featured here will do this at the expense of a current drain of only a few nano amps. A look at the circuit diagram will show that not many components are involved. Switch S1 is the "on" button and, when pressed, supplies a base drive current to the darlington transistor Ti which will then conduct to supply power to the equipment in use. Transistor T2 will now also switch on to act as latch across Si maintaining the base current to a Ti. Capacitor C1 will now start to charge via R4. When be switched off. Ub BC 516 after the voltage across...