To begin with, this Automatic Bedroom Lamp Timer Circuit turns OFF by itself and this is a very cool idea, but first we need to think about safety.
Firstly, do not touch when it is plug IN as it takes big power from wall and also this circuit is not too hard.
Moreover, 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 and people use this kind of circuit to make it look like someone is inside the room.
Also, the circuit help for safety because it seem like place is not empty even if nobody is there.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 10k 1/4 W CFR | 2 |
| 1k 1/4 W CFR | 2 | |
| 2.2M 1/4 W CFR | 1 | |
| 1M 1/4 W CFR | 1 | |
| Capacitors | PPC 0.47µF 400V | 1 |
| Electrolytic 100µF 25V | 2 | |
| Semiconductors | Transistor BC557 | 1 |
| Transistor BC547 | 1 | |
| Triac BT136 | 1 | |
| Zener Diode 12V | 1 | |
| Diode 1N4007 | 1 | |
| Push Button | 1 | |
| Bulb 220V | 1 |
First, when push button is press the C1 capacitor start charging.
After that, the BC547 gets a small current from this charged capacitor through a 2.2M resistor, even after we do not press the button.
Also, this small voltage keep BC547 ON and then BC557 also turn ON, then the triac get power from BC557 collector and then it turn ON.
When triac is ON the bulb lights up and stays ON and after some time the 100uF capacitor loses all charge and transistors stops working.
Hence, because of this delay from 100uF capacitor both transistors goes OFF, triac stop and bulb turn OFF.
So, 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 also 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 and 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:
Furthermore, this formula only is guess time if capacitor is fully discharge, but actual circuits maybe use some voltage level to decide when output goes ON or OFF.
Also, we can use this formula for simple RC delay circuits, also more complex timer circuits may need more parts and design.
How to Build:
To build a Automatic Bedroom Lamp Timer Circuit follow the below steps:
- First, place the parts on the PCB and be sure we connect them correctly.
- Next, connect positive leg anode of capacitor to one side of push button and connect other side of push button to positive rail of PCB.
- Then connect negative leg cathode of capacitor to negative supply on PCB.
- After that connect 2.2M resistor from negative rail to base of BC547 transistor.
- Then connect collector of BC547 to positive supply, connect emitter of BC547 to negative supply and connect collector of BC547 also to B base of BC557 transistor.
- Next, connect emitter of BC557 to negative supply, connect collector of BC557 to gate of triac.
- Also, connect one leg of lamp to main terminal of triac and connect other leg of lamp to negative supply.
- Finally, 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 and also 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:
Overall, we can make this Automatic Bedroom Lamp Timer Circuit on PCB by doing steps above.
Also, be sure it is safe and works good, moreover, always be careful and check all connections two times.
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