simple timer with IC 4093 + 7808

The on time of the timer is set by the one shot built with R2/R3 C3 and IC2A: after pressing pushbutton S1
C3 will be charged slowly through R3/R2; as long as the voltage of C3 is below the schmitt trigger trip level,
the output of IC2A will be high and the the relay is switched on.

Altogether the relay will switch on immediately after pressing pushbutton S1: The relay contact will take over the mains current.
The load can be switched by another relay contact (if available) or can be put in parallel with the 12V transformer
primary mains terminals
When the voltage on C3 reaches the schmitt trigger trip level, the output of IC2A will become low.
The relay will switch off the mains power supply of the timer and the load.
The timer is reset by R1 which will discharge C3 fast through D1.

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