When S1 is pressed the first monostable 555 triggers and its output goes to the high level for a time interval which depends on R3 and C2 as calculated by the following formula:
t = 1.1 x R3 x C2
At the end of this time, the output of 555 returns to the low level which causes the second monostable 555 to be triggered thereby initiating output pulse output. The duration of the pulse produced depends on R5 and C5 according to the following formula:
t = 1.1 x R5 x C5
Circuit power can be supplied with voltages from 5 to 15 V and the maximum timing values are about 1 hour using capacitors of 1 500 uF and resistors of 2.2 M ohms.
Semiconductors:
CI-1, CI-2 - 555 - integrated circuits
D1, D2 - 1N4148 - general purpose diodes
Resistors: (1/8 W, 5%)
R1- 10 k ohms
R2 - 100 k ohms
R3 - 1 k at 2.2 M ohms - see text
R4 - 47 k ohms
R5 - 1k at 2.2 M ohms - see text
Capacitors:
C1, C3, C4, C6 - 100 nF - ceramics or polyester
C2, C5 - 1 nF at 1 500 uF - see text
Several:
Printed circuit board, trigger or push button sensor, wires, solder, etc.
