Many houses can find night lights. You might even put one in the bedroom! Using a night light is a great way to avoid putting your toes on the furniture when you go to the toilet at midnight. In this interesting project, you will design and build your own night light.
You will need to build the circuit, but you also need to consider the physical design of the product. Most people may not want to place ugly bare boards around the house. Can you make a functional, aesthetically pleasing enclosure or enclosure for your circuit?
You will need to make some design decisions for the circuit. The main decision is whether to use battery or wall power. The supply voltage (3 V for 2xAA / 2xAAA / coin cell, 5 V for USB wall power) will determine the resistance required for the current limiting resistor in series with the LED.
Mini breadboard or prototype board
Power supply, such as 2xAA or 2xAAA battery holders. For wall power, you will need a USB wall adapter and a USB cable or USB male plug. You will need to connect to the USB adapter
Super bright LEDs are available in different colors.
The current limiting resistor is connected in series with the LED. You can calculate the exact value of the resistor as described in the bibliography. However, if there are already some resistors around, you can work 30–50Ω at 3 V.
Potentiometer. The potentiometer used in the example circuit has a resistance of 10 kΩ. As long as the resistance of the photoresistor does not become significantly larger or smaller, other values should also work.
Photoresistance. The photoresistor used in the example circuit has a resistance ranging from 16 kΩ (bright) to 500 kΩ (dark). Other values work as long as the other values are approximately in the same range as the potentiometer (ie, within tens of thousands of ohms). Do not use a 100Ω potentiometer with a 20MΩ photoresistor, or the circuit will not work properly.
Transistor. The transistors in the circuit are N-channel MOSFETs. There are many different types of transistors, and you can use other types to make small modifications to build this circuit. Please refer to the bibliography for more information.
Jumpers, including various kits.
To route the circuit, plan to solder the circuit to the prototype board yourself.
How does the circuit work? The potentiometer and the photoresistor are combined to form a voltage divider. The output of the voltage divider turns the MOSFET on and off based on the amount of light hitting the photoresistor (thus turning the LED on and off). The potentiometer allows you to adjust the threshold for LED lighting.