Delayed Pulse Generator This can be considered an "advanced" application where two 555 integrated circuits are used to generate a pulse of controlled duration, produced after a certain time interval. The circuit, which can drive a power load or a relay, depending on the application, is shown in the figure. When S1 is pressed, the first monostable 555 triggers and its output goes high for a time interval that depends on R3 and C2, as calculated by the following formula:
t = 1,1 x R3 x C2
At the end of this time interval, the output of the 555 will return to low level, which will cause the second monostable 555 to trigger, thus starting the production of the output pulse. The duration of the pulse produced depends on R5 and C5, according to the following formula:
t = 1,1 x R5 x C5
The circuit can be powered with voltages from 5 to 15 V, and the maximum timing values are around 1 hour with 1,500 µF capacitors and 2.2 M ohm resistors.
