An LED is turned on by a light dependent resistor LDR in a simple darkness detector circuit when it becomes dark.
In the circuit of a voltage divider, the resistor and the LDR are linked.
Because of the low voltage at the transistors base in strong light, the transistor remains off.
As night falls, the resistance of the LDR decreases, raising the base voltage and activating the transistor which illuminates the LED.
There are not many parts needed for the darkness detecting circuit, which makes it a fairly basic circuit.
Below mentioned are the list of components required for this circuit.
Circuit Working:
Parts List:
| Component Type | Description | Quantity |
|---|---|---|
| Resistors | 1k, 1/4 watt | 1 |
| 47k, 1/4 watt | 1 | |
| Semiconductors | Transistor BC547 | 1 |
| Photoresistor (LDR) | 1 | |
| LED (any 5mm, 20mA) | 1 | |
| Power Source | 9V Battery | 1 |
The light dependent resistor or LDR is the central component of this circuit.
It functions as a unique kind of dimmer switch changing its resistance in response to the amount of light it receives.
The LDR resists electricity more when exposed to bright light (high resistance) and less when exposed to darkness (low resistance).
To construct a voltage divider an additional component a resistor R2 is combined with the LDR.
This small gesture of cooperation halves the power sources incoming voltage.
The voltage that may reach the base of a transistor Q1 a crucial component of the circuit is limited by the high resistance of the LDR when the light is bright.
Similar to electrical switches, transistors regulate a greater flow of electricity with a tiny voltage at their base.
This is where the fascinating part starts the resistance of the LDR decreases with darkness.
As a result, the base of the transistor can receive greater voltage.
The transistor switches on and completes the electrical route for the LED when sufficient voltage accumulates at the base.
The LED illuminates when the way is open.
Put more simply, the circuit operates by controlling the transistor, which functions as a switch for the LED using the light sensitivity of the LDR.
The LED is turned on by the LDR flicking the switch on when it becomes dark.
Formula:
The voltage at the base of the transistor is determined by the voltage divider circuit made up of the fixed resistor and the LDR.
The voltage divider ratio formula may be used to estimate this voltage:
Vout = Vin * (R2 / (LDR+ R2))
where:
- Vout = Voltage at the output (transistor base)
- Vin = Input voltage (from power supply)
- R2 = Resistance of the fixed resistor (e.g. 47k)
- LDR = Resistance of the LDR (which changes with light)
How to Build:
To build a Simple Darkness Detector Circuit follow the below mentioned steps for connections:
- Gather all the components as mentioned in the diagram above.
- Connect collector of transistor Q1 to positive supply of +9V through resistor R1 and LED.
- Connect base of transistor Q1 between resistor R2 and LDR.
- Connect emitter of transistor Q1 to ground.
- Connect from positive supply to ground a resistor R2 and a LDR.
Conclusion:
A relatively basic circuit with a wide range of practical uses is an LDR based darkness detector circuit.
For your first electronics project this is a fantastic system that takes relatively few components.
This circuit is a subsystem that you may incorporate into your next projects.
After reading this project, I hope you are inspired to create your own darkness detector.
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