Simple Door Keyhole Light Circuit

When turned on, a tiny electronic gadget known as a simple door keyhole light circuit lights up the keyhole.

Inserting your key in dim light is made easier by this.

In order to detect the light situation for this Keyhole Light Circuit, a light sensor and circuitry are required.

In order to adjust the switching according to the light intensity, we need a transistor and an LDR (Light Dependent Resistor).

Circuit Working:

Parts List:

The circuit may be installed within any locks keyhole after it has been constructed in accordance with the above circuit diagram.

A unique light sensor LDR in the circuit senses the quantity of light in its surroundings and responds accordingly.

The resistance of the sensor rises in the dark.

Higher light levels cause the resistivity to decrease.

To operate a small switch (transistor), the circuit employs a voltage divider consisting of two resistors, one fixed and one variable the LDR.

The switch activates enabling the LED to light up, when the LDRs resistance is high and it is dark outside.

Finding the keyhole at night is made easier by the circuits automatic activation of the LED in low light, which is based on the light sensor.

To put it briefly, this circuit makes it simpler to open your door in the dark by functioning as a little automated nightlight for the keyhole.

Formulas:

The following formula can be used to create a basic circuit design for a door keyhole light circuit:

R1 (the BC547 base resistor):

The voltage drop between R1 and the base-emitter voltage VEB of the BC547 transistor define its base current IB.

To bias the transistor in the active area, a base current IB of approximately 5×10⁻³ to 10×10⁻³ times the collector current IC is appropriate.

Using a tiny signal transistor such as the BC547 and assuming that the collector current IB for driving the LED is around 10mA, you can calculate IB and hence R1 by using the following formula:

R1 = V_CC​−V_BE​​ / I_B​

where,

• The supply voltage 9V in this instance, is VCC.
• The base emitter voltage of the BC547 transistor is VBE around 0.7V.
• The base current IB is computed as I_B = I_C / β, where BC547s current gain β is normally in the range of 200 to 800.

R2 the LED current limiting resistor:

The resistor value that will restrict the current through the LED LEDI to its maximum rated current (20mA in this example) must be calculated in order to get the value of R2.

Use ohms law:

R2 = V_CC −V_LED / I_LED

where,

• The forward voltage drop of the LED is denoted by VLED for a green LED, this is usually about 2V.
• The intended LED current (20mA) is represented by ILED.

Make sure you select the right resistor values depending on the individual properties of your parts and how you want the circuit to function.

How to build:

To build a Simple Door Keyhole Light Circuit follow the below mentioned steps for connections:

• Gather all the components mentioned in the circuit diagram above.
• Connect collector of transistor Q1 to positive supply through resistor R2 and green LED.
• Connect a base of transistor Q1 between resistor R1 and LDR.
• Connect emitter of transistor Q1 to ground.
• Connect 9V batteries positive rail to positive supply and negative rail to ground.

Safety Measures:

• Work on a stable surface
• Use proper tools
• Avoid working with live circuits
• Use the correct battery type
• Keep away from children and pets

Conclusion:

To illuminate your keyhole in low light, a simple door keyhole light circuit provides an easy to use and practical solution.

The circuit automatically activates the LED as darkness descends by using a light sensor LDR and a transistor.

This makes it simpler to locate the keyhole and open your door at night.

References:

Datasheet BC547