Automatic Night Light
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A simple night light that turns on an LED automatically when it gets dark. No microcontroller needed: just a photoresistor, a transistor and two resistors on a breadboard.
Full tutorial: How To Build An Automatic Night Light Circuit
YouTube Build: https://youtu.be/mHBG2sBcyTM?si=DEB46Wu-oKXKVTJk
Automatic Night Light Schematic
The photoresistor and R1 form a voltage divider that drives the base of the transistor.
- In light, the photoresistor has a low resistance, so the voltage at the base stays low (around 0.5V). The transistor is off and the LED is dark.
- In the dark, the photoresistor's resistance goes up, the base voltage rises, and the transistor turns on. Current flows through R2 and the LED, and the LED lights up.
R2 limits the current through the LED so it doesn't burn out.
Automatic Night Light Parts List
How to Build the Automatic Night Light
You can biuld this on a breadboard like shown below.
Tips:
- To adjust when the light turns on, replace R1 with a potentiometer.
- If the LED stays on all the time, your photoresistor may have too high a resistance in light. Try a lower value for R1 (somewhere between 1 kΩ and 10 kΩ).
- It also works on 5V. Reduce R2 a little if the LED is too dim. On 12V, increase R2 to 1 kΩ.
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