A simple dark sensor circuit designed for security purposes uses the timer IC 555
This electronic design can detect low light levels and activate a response such as turning on a buzzer or a light.
It employs a standard light-dependent resistor LDR to sense light.
This circuit is quite handy for various security applications such as automatic night lights and alert systems.
The setup features the IC 555 timer chip, an LDR and a few other simple components.
It can be conveniently powered by a 9V PP3 battery.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors 1/4 watt | 100k, 1M | 1 each |
| Potentiometer | 1k | 1 |
| LDR | – | 1 |
| Capacitors | Ceramic 1000pF | 1 |
| Semiconductors | IC 555 | 1 |
| Buzzer | – | 1 |
| Battery | 9V | 1 |
This simple dark detector circuit is based on how a Light Dependent Resistor LDR changes its resistance with the amount of light present.
When it is bright outside the LDR has low resistance, which lets more current flow and keeps the IC1 timer from working.
But when it gets dark the resistance of the LDR increases, which changes the voltage at pin 2 of the IC1 555 timer.
This change makes the timer turn on in monostable mode causing the buzzer to beep as a warning.
Formulas with Calculations:
Below are the formulas with calculations for Simple Dark Sensor Circuit for Security using IC 555 timer:
Threshold Voltage Calculation:
The voltage divider formed by R2 and the LDR determines when the IC1 555 triggers:
Vpin2 = (R2 / (R2 + R3)) * Vsupply
where,
- Vpin2 is the voltage at pin 2
- R2 and R3 form a voltage divider
- Vsupply is the supply voltage of the circuit
In bright light R3 LDR is low, so Vpin2 is high.
In darkness R3 increases lowering Vpin2 triggering the 555 timer.
Time Delay Calculation:
The timing delay can be calculated using:
T = 1.1 * R1 * C1
where,
- T is the output pulse duration how long the output remains HIGH after being triggered
- R1 is the timing resistor 100k in ohms
- C1 is the timing capacitor 1000pF in farads
- The constant 1.1 comes from the internal design of the IC1 555 timer.
Substituting values:
R1 = 100k ohms and C1 = 1000pF
T = 1.1 * 100000 * 0.000000001
T = 0.11 milliseconds
How to Build:
To build a Simple Dark Sensor Circuit for Security using IC 555 timer follow the below mentioned steps:
- Assemble all the components as mentioned in the above circuit diagram
- Connect pin 1 of IC1 to GND of the circuit
- Connect pin 2 of IC1 to pin 6 of IC1
- Connect a resistor R2 between pin 2, 6 and pin 3 of IC1
- Connect pin 3 of IC1 to one terminal of VR1 pot and other end of VR1 connect to one end of buzzer and other end of buzzer connect to GND
- Connect pin 4 and pin 8 of IC1 to positive supply of +9V battery
- Connect a resistor R1 between pin 4 and pin 8 of IC1
- Connect a capacitor C1 from pin 2 and GND
- Connect a LDR R3 between pin 4 and GND
Conclusion:
This Simple Dark Sensor Circuit for Security using IC 555 timer is an easy and efficient method to detect darkness and activate an alert system.
You can change the resistor values to adjust how sensitive the circuit is.
This circuit is great for home automation, security systems and saving energy.