Fast Starting Wiper Delay

05 FAST STARTING WIPER DELAY A wiper delay is essentially a bistable multivibrator whose off-time is adjust- able with a potentiometer. Many wiper delay circuits are based on the Type 555 timer in its standard application circuit, which has the disadvantage of introduc- ing a delay of about 1.6 times the set in- terval before the first wiper action takes place. This is especially annoying when an interval of, say, ten or more seconds has been set. This circuit is also 555 based, but is unique in that it arranges for the wipers to be activated immedi- ately at power-on. The circuit diagram of Fig. 1 shows the internal organization of the 555 timer to aid in clarifying the operation of the present circuit. When S1 is closed, pin 6 is immediately pulled to +12 V because C, is discharged as yet (see also Fig. 2b). The bistable in the 555 is reset, the output goes low, and Re, is energized. This forms the basic difference with the standard application of the 555, where Cl, connected as...