Simple Alternate Red Green LED Flasher Circuit

This post shows you how to build a flashing LED light circuit with red and green LEDs.

These are popular electronic projects because they are fun and easy to make.

The circuit uses two special parts called transistors to make the LEDs blink on and off in an alternating red green pattern.

What is a Alternate Red Green LED Flasher Circuit:

An alternate red green LED flasher circuit is a simple electronic circuit that alternately flashes red and green light emitting diodes LEDs.

This type of circuit is often used for decorative purposes, such as in holiday decorations or signaling applications where a visual alternation between red and green lights is desired.

How the Circuit Works:

Parts List:

The BC547 transistors are configured as an astable multivibrator creating a square wave output.

This alternating output drives the LED strings connected to the collectors of the transistors.

The 10uF capacitors and 47k ohm resistors determine the frequency of the flashing.

Adjusting these values can alter the flashing speed.

The 47 ohm resistors in series with the LED strings limit the current and protect the LEDs.

The LEDs are connected in series to ensure that they share the same current.

The anodes of both the red and green LED strings are connected to the positive line and the cathodes are connected to the collectors of the transistors.

Power Supply:

Use a 12V DC power supply to energize the circuit.

Ensure that the positive and negative terminals are connected correctly to avoid damaging the components.

Testing:

Upon connecting the power supply, the circuit should start flashing with alternate red and green LED sequences.

If adjustments to the flashing speed are desired experiment with different capacitor and resistor values in the astable multivibrator configuration.

Formulas and Calculations:

Below mentioned are general formulas that govern the frequency of astable multivibrators:

Frequency of Astable Multivibrator:

f = 1 / (1.4 * (R₁ + R₂) * C)

where,

• f: Frequency of the output square wave
• R₁ & R₂: Timing resistors 47k
• C: Timing capacitor 10uF

Calculations:

Resistors R1 & R2: 47k both resistors have the same value.

Capacitor C: 10uF

f = 1 / (1.4 * (R₁ + R₂) * C)

1. Total Timing Resistance: Since both resistors R1 & R2 have the same value, add them together:

Total Resistance (R) = R₁ + R₂ = 47kΩ + 47kΩ = 94kΩ

2. Plug in the values:

f = 1 / (1.4 * 94kΩ * 10uF)

3. Unit Conversion: Convert nanoseconds (ns) to hertz (Hz) for frequency, we can estimate by dividing by 1 billion (1,000,000,000) because 1nF * 1kΩ = 1ns.

f = 1 / (1.4 * 94,000 * 10 * 10^-9) = 1 / (1.316 * 10^-6)
f = 7.6 (rounded to one decimal place) Hz

Consequently, 7.6 Hz is the approximate frequency of the square wave output produced by the astable multivibrator circuit.

This implies that there will be around 7.6 flashes per second for each LED (red and green).

Note:

Recall that because of the restrictions of the formula and possible fluctuations in component values, this is an estimate.

The actual frequency of flashing may vary significantly.

How to Build:

To build a Simple Alternate Red Green LED Flasher Circuit follow the below mentioned steps:

Transistor Connections:

• Connect the emitters of both BC547 transistors to the ground negative line.
• Connect the collector of both transistors to the positive line through their respective 47 ohm collector resistors.
• Connect the bases of both transistors to the junction of their corresponding 10uF capacitors and 47k ohm base resistors.

LED Connections

• Connect four green 5mm LEDs in series with a 47 ohm resistor across the collector of one BC547 transistor.
• Connect four red 5mm LEDs in series with another 47 ohm resistor across the collector of the second BC547 transistor.
• Connect the anodes of both the red and green LED strings to the positive line.

Applications

• Use the red green LED flasher in decorative lighting arrangements for holidays, events, or home decor.
• The alternating colors add a dynamic and eye catching element to displays.
• Implement the circuit in signaling applications where alternating colors are used to convey information.
• For example, in alarm systems or status indicators where red and green signify different states or conditions.

Conclusion:

Building an alternate red green LED flasher circuit is a rewarding project for electronics enthusiasts.

This simple yet effective circuit provides a visually appealing flashing pattern making it suitable for various decorative and signaling applications.

Experiment with different component values to customize the flashing speed and create a unique visual effect.

References

Multivibrator

RGB led astable circuit