When the sensor doesn’t receive any light (night time), the transistor basis would have 1 (high) value, so the emitor value is 0 (low). The low value in the emitor would reset the IC timer. The circuit’s value would change when the sensor exposed by morning light. This condition would turn on the IC555 and produce sound on the speaker. Sensor sensitivity can be adjusted by turning the variable resistor to find the proper value.
Components :
Resistor R1 : 10k ohm
Resistor R2 : 3K3 ohm
Resistor R3 : 56k ohm
Resistor variable VR1 : 100k ohm
Transistor TR1 : BC158
Polar capacitor C1 : 1uF/15V
Capacitor C2-C3 : 0.01 uF
IC timer : NE555
LDR light sensor
Speaker : 8 ohm/0.5W
ON/OFF switch
9V power supply
