Engineer an LED Night-Light

AREAS OF SCIENCE

Electricity & Electronics

DIFFICULTY

METHOD

Engineering Design Process

TIME REQUIRED

Short (2 days)

Night-lights can be found in many homes; you might even have one in your bedroom! Using a night-light is a great way to avoid stubbing your toe on furniture during a midnight trip to the bathroom. In this fun engineering project, you will design and build your own night-light. You will need to build the circuit, but you will also need to think about the physical design of the product. Most people probably do not want an ugly, bare circuit board sitting around their house. Can you make a functional, aesthetically pleasing case or enclosure for your circuit? You could make a case using craft materials, wood, or even a 3D printer if you have access to one.

If you need some help getting started and learning how to build an LED night-light circuit, first watch this video for an overview and explanation of how the circuit works.

A mini breadboard for building the circuit.
A 2xAA battery pack to power the circuit.
Super bright LEDs in a variety of colors.
A current-limiting resistor to prevent the LED from burning out.
A potentiometer, which allows you to set the light threshold for the circuit to turn on.
A photoresistor, also called a light-dependent resistor (LDR) or photocell. Its resistance changes in response to ambient light.
A transistor, which acts as an electronic control valve to turn the LED on and off.
A jumper wire to make a required connection on the breadboard.

To wire the circuit, see the diagrams in Figures 1 and 2. Figure 1 shows the connections directly between the leads of the different circuit components. You can use this diagram if you plan to solder the circuit yourself on a protoboard (you will need to decide how to arrange the components). Figure 2 shows the circuit on a breadboard. You can follow this diagram exactly.

Figure 2. Breadboard diagram for LED night-light circuit. Image made with Fritzing.

How does the circuit work? Remember to watch the video (starting at about 3:25) for an explanation. Figure 3 shows a copy of the schematic. See the Bibliography if you do not know how to read a circuit schematic. The potentiometer and photoresistor are combined to form a voltage divider. The output of the voltage divider turns the MOSFET on and off (therefore turning the LED on and off) depending on the amount of light hitting the photoresistor. The potentiometer allows you to adjust the threshold at which the LED will turn on.

Figure 3. Circuit schematic for the LED night-light.