Simple Dark Sensor Circuit for Security using IC 555 timer

Simple Dark Sensor Circuit for Security using IC 555 timer is useful project for security.

It senses low light and turns ON the buzzer or light.

It is used for LDR as light sensing.

Circuit is good for night light and alert system.

The circuit have parts like 555 IC, LDR, resistors, capacitor and buzzer

It work with 9V battery.

Circuit Working:

Component	Specification	Quantity
Resistors (All resistors are 1/4 watt)	100k, 1M	1 each
	Potentiometer 1k	1
	LDR	1
Capacitor	Ceramic 1000pF	1
Semiconductors	IC 555	1
	Buzzer	1
	Battery 9V	1

This circuit for dark detector works on LDR change resistance with light.

In bright light the LDR is with low resistance and with more current flow and keeps IC1 from working

In dark the LDR is with high resistance and voltage at pin 2 changes.

This make 555 timer turn ON in monostable mode and buzzer beeps as warning.

Formula for dark sensor:

Threshold Voltage:

Vpin2 = (R2 / (R2 + R3)) × Vsupply

R2 + LDR R3 make voltage divider.

In bright light the LDR is low and Vpin2 is high.

In dark the LDR is high and Vpin2 is low and 555 IC timer triggers.

T = 1.1 × R1 × C1

where,

To build a Simple Dark Sensor Circuit for Security using IC 555 timer follow the below mentioned steps:

Assemble all parts as per circuit diagram.
Connect pin 1 of IC1 to GND of circuit.
Connect pin 2 of IC1 to pin 6 of IC1.
Connect resistor R2 between pin 2 and pin 6 and pin 3 of IC1.
Connect pin 3 of IC1 to one terminal of VR1 pot and connect other terminal of VR1 to one end of buzzer and connect other end of buzzer to GND.
Connect pin 4 and pin 8 of IC1 to +9V battery positive.
Connect resistor R1 between pin 4 and pin 8 of IC1.
Connect capacitor C1 from pin 2 to GND.
Connect LDR R3 between pin 4 and GND.

Simple Dark Sensor Circuit for Security using IC 555 timer detect dark and turns ON an alert.

It changes resistor for sensitivity.

Circuit is good for home automation, security and energy saving.