Blinky Christmas Tree DIY

Introduction

This circuit simulates the blinking light of a Christmas Tree. It consists of 16 LEDs, 8 red and 8 green, divided into 4 zones that blink at different frequencies. Unlike other blinking light generator circuits that use integrated circuits, the circuit in this kit uses only transistors as active elements. It can be powered by a 9V battery and used as a standalone device.

List of tools required for assembly and operation,
not included in the kit

List of components included in the kit

Schematic

Working principle

The circuit is composed of two bistable multivibrators (flip-flop):

• The first one is formed by transistors Q1 and Q2, along with capacitors C1 and C2, and intermittently controls the branches of LEDs LED4-LED14 and LED6-LED12.
• The second one is formed by transistors Q3 and Q4, along with capacitors C3 and C4, and intermittently controls the branches of LEDs LED4-LED14 and LED6-LED12.

Each bistable, as the name suggests, has two states. In our case, these states are intermittent. With two bistables, each having two states, we have a total of 4 states that form the light game.

Observing the blinking light, we can see that the 4 states have different frequencies. The frequency of a state change depends on the voltage between the base and emitter of the tranzsitors. Both bistables are powered at the same voltage, have capacitors and resistors of the same values, and the same number of LEDs… what makes the base-emitter voltage of the two bistables differ? Well, it’s the color of the LEDs. Green LEDs have a higher voltage drop than red LEDs. Thus, we have an imbalance, a difference in voltage between the two bistables, resulting in different blink frequencies.”

Instructions for assembly preparation

Assembly instructions