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Simple Automatic Bedroom Lamp Timer Circuit

Simple Automatic Bedroom Lamp Timer Circuit turns OFF by itself and this is a very cool idea.

But first think about safety.

Do not touch when it is plug in as It takes big power from wall.

This circuit is not too hard.

When we press button then many parts start working together.

What is a Automatic Bedroom Lamp Timer Circuit:

This circuit for bedroom lamp timer can turn lamp ON and OFF by itself.

People use this kind of circuit to make it look like someone is inside the room.

It help for safety because it seem like place is not empty even if nobody is there.

Circuit Working:

Parts List:

CategoryItemQuantity
Resistors10k 1/4 W CFR2
1k 1/4 W CFR2
2.2M 1/4 W CFR1
1M 1/4 W CFR1
CapacitorsPPC 0.47µF 400V1
Electrolytic 100µF 25V2
SemiconductorsTransistor BC5571
Transistor BC5471
Triac BT1361
Zener Diode 12V1
Diode 1N40071
Push Button1
Bulb 220V1

When push button is press the 1000uF 25V capacitor start charging.

The BC547 get small current from this charged capacitor through 2.2M resistor even after button is not pressed.

This small voltage keep BC547 ON and then BC557 also turn ON.

The triac get power from BC557 collector and then it turn ON.

When triac is ON the bulb lights up and stays ON.

After some time the 100uF capacitor loses all charge and transistors stops working.

Because of this delay from 100uF capacitor both transistors goes OFF, triac stop and bulb turn OFF.

To make it work again we need to press button again.

But after this lamp will not work anymore.

Formulas:

The formula below show how resistor (R) and capacitor (C) give delay time (t) in basic RC circuit.

This formula is only for delay OFF time.

Delay OFF Time (t):

t = R × C

where:

How formula work:

When Charging Capacitor:

When circuit get trigger like voltage change capacitor start charging through resistor.

Slowly voltage across capacitor goes up.

Example:

Say we have delay OFF timer with:

Capacitor = 1μF (microfarad)

Resistor = 10kΩ (10,000 ohms)

Use formula:

t = R × C = 10,000Ω × 1μF

Change microfarad to farad:

1μF = 0.000001F

t = 10,000 × 0.000001 = 0.01 seconds

So delay OFF time is 0.01 seconds (or 10 milliseconds).

Note:

This formula only guess time if capacitor is fully discharge.

But actual circuits maybe use some voltage level to decide when output goes ON or OFF.

We can use this formula for simple RC delay circuits.

More complex timer circuits may need more parts and design.

How to Build:

To build a Simple Automatic Bedroom Lamp Timer Circuit follow the below steps:

Testing:

Modify Delay:

Be Careful:

Conclusion:

We can make this Simple Automatic Bedroom Lamp Timer Circuit on PCB by doing steps above.

To be sure it is safe and works good but always be careful and check all connections two times.

References:

Datasheet BT136

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