Having a night light that turns on automatically when it detects motion can be incredibly convenient. Not only does it eliminate the need to get up and turn on a light switch in the dark, but it also provides added security by illuminating an area when movement is detected. Best of all, such a handy gadget can be built using just a few basic components for under $5.
Supplies Needed
Constructing a motion-activated night light requires just a few simple supplies:
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PIR motion sensor - This sensor detects infrared radiation from movement and allows the circuit to be automatically activated. They can be purchased for just a couple dollars.
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LED bulb - Any small LED bulb can be used. I'm using a 5mm white LED bulb in this project.
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Resistor - The resistor is needed to prevent too much current flowing to the LED. I'm using a 220 ohm resistor.
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Jumper wires - Jumper wires allow connections between components on a breadboard.
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9V battery - Provides power to the circuit.
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9V battery clip - Connects the 9V battery to the circuit.
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Breadboard - Used to easily prototype circuits without soldering.
In total, all of these components can be purchased for around $5. Now let's look at how to put them together.
Circuit Design
The circuit for this motion-activated night light is very simple, with just a few key components:
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The PIR sensor detects motion and outputs a signal when triggered.
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This signal is sent to the base of a NPN transistor which turns it on.
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When the transistor is on, it allows current to flow from the 9V battery through the LED and resistor to ground, lighting up the LED.
Here is a circuit diagram showing how the components are connected:
The resistor is needed to limit the current through the LED to prevent burning it out. The value can be tweaked to make the LED brighter or dimmer.
Constructing the Circuit
Step 1) Insert the 9V battery clip wires into the breadboard. Connect the red wire to the power bus strip and the black wire to the ground bus strip.
Step 2) Insert the PIR sensor's three pins into the breadboard. The pin order will be ground, signal, and power.
Step 3) Connect the signal pin from the PIR to Pin 2 of a general purpose NPN transistor, like the 2N2222. Leave Pin 1 unconnected and connect Pin 3 to ground.
Step 4) Insert the LED into the breadboard, noting which leg is positive (longer) and which is negative. Connect the positive leg through a 220 ohm resistor to the 9V power bus. Connect the negative leg to Pin 1 of the transistor.
Step 5) That completes the circuit! The PIR sensor will detect motion and output a signal to the transistor to turn on the LED.
Testing and Using the Motion-Activated Night Light
Once constructed, gently wave your hand in front of the PIR sensor. The LED should illuminate! Cover the sensor to turn it off again.
You can tweak the sensitivity of the sensor and the brightness of the LED by adjusting component values until you're satisfied.
To use your motion-activated night light, simply power it using the 9V battery and place it in any dark area you want to have illuminated when motion is detected. Wave your hand in front of the sensor to test and ensure it works properly.
Some ideas:
- Place it in a dark hallway or corridor
- Use it to highlight a path outdoors
- Put it in a closet or cupboard to light up when opened
Adjusting the sensor's sensitivity prevents false triggering while ensuring it detects real motion. Angle and position it for optimal coverage.
With just a few basic electronic components, you can build an automatic night light on the cheap for added convenience and security!