Many electronics circuits and projects for learning in simple ways.

# Blinking 2 LED circuit using NPN transistors

I like Blinking 2 LED circuit using NPN transistors. There are many circuits here is one of the blinking circuits. We call it Astable Multivibrator. Often we know it 2 LED Flasher circuit, in this we use PNP transistor.

But now we use 2 NPN transistor. We normally see it in a lot of circuit as oscillators. Both transistor work alternately likes the automatic switches that are alternate working. The collector of Q1 or Q2 makes the frequency signal.

Operation of the circuit
To begin with, suppose that the Q1 run first. Then LED1 should grow more brightly.
It makes the current to flow through LED1, R1, and the collector-emitter of Q1. At the same time, some current will flow through LED2, R4, and to charge into C2 until full. The voltage BE is lower than 0.7V. So Q1 turns off, LED1 goes out.

Next Q2 start working, LED2 also grows more brightly. The C1 begins to charge until full, VBE of Q2 is lower than 0.7V. It turns off, LED2 goes out.

After that Q1 will turn on and LED1 to grow up again. the circuit working will repeat loop in like this.

The bicycle tail light for my son.
The principle of this circuit, I built the bicycle tail light flashing for my son. At first, he was very appreciated. But he embarrassed every time, friends to tease. Because it’s funny. I used a hot food box because preventing water heat resistant and very economical. And more importantly, it increases the safety of the children. When riding a bicycle in the evening.

## 3V Blinking LED circuit using transistor

My son wants to build a simple blinking LED. I choose the 3V blinking LED circuit.  Because it is so easy. We can assemble all components on a breadboard. And use 3V AA battery.

In the circuit below. We use BC549 transistor and not need Resistor limit current to LEDs.