Learn LDR automatic LED flashlight

How to quickly learn transistor and LDR circuits?
In this post, I am going to show you how easy learning.

My son wants to build a simple automatic flasher. It is special. Why?

It will be light in the dark. This circuit uses 5 parts only and cheap.

He likes to play LEGO very much. So builds the Lighthouse tower with LEGO block.

It is not important for you. Even more importantly.

I hope this helps you improve understanding it works. For example, the voltage divider circuit, resistor works, and more.

Ready to get started?

How circuit works

automatic LED flashlight


As Figure 1, this circuit uses the simple transistor driver for flashing LED.

He uses the Multicolor Flashing LED for LED1

How to build

He assembles them on a small breadboard as Figure 2. When applying the 2.4V power supply to the circuit. The small current flow through to R-10K to the base lead of transistor Q1- 2N3904, makes large current flow through the collector to emitter lead, and LED1 will glow up. As Figure 3.

Assemble the circuit on breadboard


Figure 2 assemble the circuit on a breadboard

LED glow up


Figure 3 LED glow up

Then, he put LDR into the circuit as Figure 4. When the light to LDR, its resistance is low. So the R1’s current flow through to LDR instead. It makes no current to the base of transistor so it not work. LED will go out.
And after, he turns off the lamp. The resistance of LDR is high, so the R1’s current can flow through the base of the transistor again. It makes large current from collector flow to the emitter of the transistor so LED glow up or flashing light.

lego-automatic-led-flasher-light

Figure 4 Lego automatic LED flasher light circuit

As video below he builds and make them!

It is first video that he speak English

How to learn electronics with simple ways

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This Post Has 3 Comments

  1. Awesome Circuit!!!!!!!!!!!

  2. KVL And KCL circuit

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