switching delay - for filming and other applications

for filming and other applications It is sometimes required that one of two parallel-operating units is switched on just after, and switched off just before, the other. An example is in film or camera work where the lights must be switched on just before the camera, and switched off just after it. The present circuit provides such a delay. Because the IC we used contains four NAND schmitt triggers, of which only two are needed for the delay circuit, we took the oppor- tunity of providing a debouncing latch. In the circuit diagram, N1/N2 form the debouncing latch, and N3/N4 the delay circuit. Suppose that switch S1 is in the off position. The output of N2 is then low, capacitors C1 and C2 are discharged, and the outputs of N3 and N4 are high. The base potential of p-n-p transistors T1 and T2 is then almost equal to the emitter voltage so that the transistors are cut off and the relays, Re1 and Re2, are at rest. When S1 is turned on, the output of N2 becomes high, and C2 is charged ...