Night Light

Automatic Night Light Circuit Project

Created by: Aakash Bathini
Edited by: Satyam Goyal

This instruction guide will take you through the steps to creating your own automatic night light. The design utilizes a light-dependent resistor that will turn on the white LED when a lack of light is detected. It is a simple circuit that you can build on a breadboard. Review the parts list below and once you have all your materials organized, you can start the building process.

Parts List

(2) BC 548 Transistors
(1) White LED
(1) Light Dependent Resistor (LDR)
(1) 100 Ohm Resistor
(1) 4.7k Ohm Resistor
(1) 1k Ohm Resistor
(1) Breadboard
(1) 9V Energizer Alkaline Battery
(1) 9V Battery Holder with Cover and Switch and 6 Inch Wires
(1) 70-Piece Jumper Wire Kit - 14 Lengths 10 Colors

Tools: Wire Strippers

Step 1 Transistors

Connect two BC 548 transistors horizontally on row H. Note the names of the transistor’s 3 pins listed on the diagram. Leave a 3-hole gap between the transistors and a 1-hole gap between pins in the same transistor. The emitter of the leftmost transistor should be on column 13 and the collector of the rightmost transistor should be on column 25. The flat side of the transistors should be facing toward rows I and J. Connect the light-dependent resistor vertically in column 24 with one wire on the positive rail and the second on a pin in row A.

Automatic Night Light Transistors

Step 2 Resistors 1k Ohm

Connect the 1k ohm resistor with one wire on the rail and the other wire in line with the rightmost collector (row 25, column G). Use a wire to connect the LDR to the base pin of the right transistor (the wire should go from column 24 row C to column 23 row G).

Automatic Night Light Resistor 1K

Step 3 Resistors 4.7k Ohm

Connect the 4k ohm resistor in line with the right transistor’s base (column 23). One of the resistor’s wires should be on the negative rail (upper) and the second should be in row J. Use 1 wire (yellow as shown in the image) to connect the negative rail to the right transistor’s emitter (column 21 row J). Use another wire (green as shown in the image) to connect the negative to the left transistor’s emitter (column 13 row I).
Automatic Night Light Resistor 4.7K

Step 4 Wire Connections

Use 1 wire (brown as shown in the image) to connect the right transistor’s collector to the left transistor’s base (row I). Connect the 100-ohm resistor vertically in line with the left transistor’s base (column 15). One of the resistor’s wires should be on the bottom rail and the second should be on row C.

Connect the white LED inline vertically with the 100-ohm resistor (column 15 row E to F). Keep in mind that the longer of the LED’s wires is the positive end (cathode) and the shorter is the negative end (anode). The cathode end of the LED should be closer to the resistor and the anode end of the resistor should be closer to the transistor.

Step 5 Battery Attachment

Automatic Night Light Wire

Attach the 9V battery to the battery lid and re-screw the lid. The red wire is positive and the black wire is negative. Attach the positive wire to the positive rail (bottom) and the negative to the negative rail (top). Make sure these are on the bottom-most hole and top-most hole of their respective rail. Once everything is securely fastened, switch on the battery, turn off any light sources, and watch as your night light comes to life!
Automatic Night Light Battery Case

Automatic Night Light Final Project

For more information, watch the video below!