We all have night lights right besides our beds. If not, we have to walk in dark to the bed after we switch off the lights in the bed room. Well if you build this circuit there will not be such problems. What this circuit do is keep a delay time before turning off the light. We are going to demonstrate this using a LED but you can adapt it anywhere you want. The main component of this project is D882 transistor. This is a NPN transistor. You can see the pinout and the physical appearance of the D882 transistor in the image.

Supplies

Below list is consist with all the key components we are going to need in this project. For your convenience all the components are provided with links from UTSource So, you can simply order the components.

⦁ 10kΩ resistors
⦁ 100Ω resistors
⦁ D882 Transistor
⦁ 1000µF 10V Capacitor
⦁ Push button
⦁ LED
⦁ Circuit wire

Other tools that you might need: Soldering Kit.

Step 1: PinOuts:

Step 2: Circuit Diagram:

This is the circuit diagram of the delay night light. D882 is the controller of the LED. As you can see LED is connected to the 3.7V positive pin and the 100Ω resistor. This resistor is to limit the current through the LED. The remaining pin of the LED is connected to the collector of the D882 transistor. Base pin is connected to the 10kΩ resistor and it is then connected to the push switch. A 1000µF capacitor is also connected to this point and ground. Emitter of the D882 transistor is connected to the ground.

Step 3: Assembly:

1. Connect negative pin of the 1000µF 10V capacitor to the emitter pin of the D882 transistor.

2. Solder the collector pin of the D882 transistor to the 100Ω resistor.

3. Solder the base pin of the D882 transistor to the 10kΩ resistor.

4. Solder the positive pin of the LED to one of the push buttons pins.

5. Solder the remaining pins of the push button and the LED as shown in the circuit diagram.

6. Connect the 3.7V battery to the circuit as shown in the circuit diagram.

Step 4: How It Works:

When the button is pressed the capacitor is charged and the base of the D882 transistor is also triggered. As the base is triggered LED will turn on. AS the capacitor is charged it will provide a base current even when the switch is disconnected. So, the LED will remain on till the charge of the capacitor is remaining. You can change the delay time by changing the value of the capacitor

Conclusion:
You can use as a simple nightlight. Or you can use a relay instead of a LED and control AC loads using this circuit as well.