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:

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:

• t is delay OFF time in seconds and how long output take to turn OFF after trigger goes away.
• R is resistor value in ohms Ω.
• C is capacitor value in farads F.

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:

• Place parts on PCB and be sure all are connected right.
• Connect positive leg anode of capacitor to one side of push button.
• Connect other side of push button to positive rail of PCB.
• Connect negative leg cathode of capacitor to negative supply on PCB.
• Connect 2.2M resistor from negative rail to B base of BC547 transistor.
• Connect C collector of BC547 to positive supply.
• Connect E emitter of BC547 to negative supply.
• Connect C collector of BC547 also to B base of BC557 transistor.
• Connect E emitter of BC557 to negative supply.
• Connect C collector of BC557 to gate of triac.
• Connect one leg of lamp to main terminal of triac.
• Connect other leg of lamp to negative supply.
• Connect positive and negative wires from power supply to the PCB rails properly.

Testing:

• Press the push button.
• The lamp should turn ON and stay ON for some time depends on 2.2M resistor and 100uF capacitor.

Modify Delay:

• Change resistor and capacitor values to get more or less delay time.
• Check all wires and parts with no loose connection.

Be Careful:

• Do not touch circuit when it has power especially with AC power which can be dangerous.

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