| VR1 and the Light
Dependent Resistor (LDR) form a potential divider at the input.
A falling light level on the LDR changes its resistance. This causes the voltage to change at pin 2. The 555 is activated, pin3 going low to energise the relay. Reversing the LDR and VR1, as shown on the left, will reverse the circuit action, causing the relay to energise as the light increases. |
Copyright Graham Knott 2002