visible power-on delay

by R Jacobs 93 visible power-on delay While in the process of repairing or scope probe or test lead to the part in testing electronic equipment, it is • question, after power has been ap- often desired to have more time plied. available for hooking up an oscillo- This circuit gives you plenty of time to reach any component in the cir- cuit, since the equipment is only switched on after a fixed interval fol- lowing depression of the start button. O C) CI P" J) Jp, R8...R17 = 10k R18...R27 = 390k T1 ...T 10 = BC547B 2 cs Ca CI l gT N1...N4 =1C 1 = 4093 N5...N7 = IC2 = 4025 131 IC 1 IC 2 IC3 The basic operation of the circuit is as follows. Activating start switch Si sets the bistable composed of N2 and N3, causing N3 to provide clock pulses to decade counter IC3. The driver transistors at the outputs of this IC will light the LEDs one after another, indicating the countdown function of the circuit. Rei is ener- gized the moment the last LED in the row lights; IC3 is disabled via...