This is a delay timer that upon powering up waits for a set period of time and then turns on the controlled device through the optocoupler (or relay).
The way it works is when power is turned on C1 is charged through R1 and when the voltage of C1 reached the zener voltage of D1, D1 starts to conduct and turns on Q1. Which then completes the optocoupler part of the circuit and turns on the output.
The length
of the delay is set with R1, C1, D1, or changing the supply voltage. The delay
for the timer can be determined mathematically with the following formula:
Delay =(((Vz+0.6)/Vs)/0.63)*RC
Delay =
total delay of the timer (in seconds)
Vz = Zener voltage of D1
Vs = Power Supply Voltage
R =
Resistance of R1 (in MO)
C = Capacitance of C1 (in µF)
