""On"" Indicator

10 011 GENERAL INTEREST Battery-operated equipment can work on one set of batteries for a long time nowadays. But if it is left on inadvertently, that "long time" is over very quickly. Moreover, flat batteries are always found at the wrong moment. The circuit pro- posed here is a sort of aide-mem- oire. Every two minutes it emits 5-10 pips to indicate that the equip- ment is still switched on. utes. That output is inverted so that N4, like N2, can only be enabled during the 10-second pulse train from Ni. There is a difference, though: during those 10 seconds, N4 is enabled and inhibited ten times and this is what causes the pips. Do not take the times and num- ber of pulses too literally, because there are wide variances between ics from different manufacturers. On the other hand, component values are not critical, so that it is fair- ly easy to adapt the circuit to personal taste or requirements. The buzzer may be a standard Toko type or equivalent. Finally, the current drawn by ...