versatile timer

1511versatile timer This simple-looking circuit enables the arbitrary programming of seven outputs in a series of not more than 2048 (211) steps. The step length may be set as required. The time base is derived from the mains voltage. Tran- sistor Ti produces a square wave from the mains voltage applied to its base. This square-wave voltage is div- ided by 10 in ICI, so that the fre- quency of the signal at the clock input of IC2 is 5 Hz. Circuit IC2 serves as address counter for the Type 2716 EPROM. This means that IC2, after a reset, counts upwards from 0 and runs over the successive addresses of the EPROM. Circuit IC2 has twelve outputs which would enable the use of a Type 2732 (4096 steps), but, on practical and financial grounds, a Type 2716 is used here since 2048 steps are nor- mally quite sufficient. The outputs of the EPROM are buf- fered by a Darlington array, ICs, so that seven switch outputs are available with a sink capacity of R1 50 Hz 11-11 16 16 241 21 EE July/Au...