Lego automatic LED flashlight

Today my son wants to build the simple automatic flasher circuit. It is special that it will be light on dark. This circuit uses 5 parts only and cheap. He likes to play LEGO very much so builds Lighthouse tower by LEGO block.

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

He uses the Multicolor Flashing LED for LED1

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.

automatic LED flashlight

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.


Figure 4 Lego automatic LED flasher light circuit

As video below he builds and make them!

It is first video that he speak English

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MR OHM 1970

Awesome Circuit!!!!!!!!!!!


KVL And KCL circuit

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