The circuit diagram present here is that of a street light that automatically switches ON when the night falls and turns OFF when the sun rises. In fact you can this circuit for implementing any type of automatic night light.
The circuit uses a Light Dependent Resistor (LDR) to sense the light .When there is light the resistance of LDR will be low. So the voltage drop across POT R2 will be high. This keeps the transistor Q1 ON. The collector of Q1(BC107) is coupled to base of Q2(SL100). So Q2 will be OFF and so do the relay. The bulb will remain OFF.
When night falls the resistance of LDR increases to make the voltage across the POT R2 to decrease below 0.6V. This makes transistor Q1 OFF which in turn makes Q2 ON. The relay will be energized and the bulb will glow.
Circuit Diagram of Street Light Project
Street Light Circuit Diagram
List of Circuit Component
R1 – LDR
R2 – 100K Preset
R3 – 1K
R4 – 1K
Q1 – Bc107
Q2 – SL100
K1 – 9V SPDT Relay
F1 – 1A Fuse
L1 – 230V Lamp
230 V AC Mains
POT R2 can be utilized to change the affectability of the circuit.
You can utilize bulb of any wattage, given that transfer ought to have the adequate rating.
The circuit can be fueled from a directed 9V DC power supply.