Simple Alternate Red Green LED Flasher Circuit

This post explains how to build a flashing LED light circuit using red and green LEDs.

Because it is enjoyable and simple to use it is a most favored electronic project.

This circuit uses two specific BC547 transistors which are the main reason for alternate flashing of red and green LEDs.

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 LEDs.

This kind of circuit is often used for decorative purposes including in signaling applications or holiday decorations where a visual change between red and green lights is needed.

Circuit Working:

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 measure 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:

A 12V DC power source is used to drive the circuit.

Make sure the positive and negative terminals are connected correctly to prevent component damage.

Testing:

The circuit should begin flashing with alternating red and green LED sequences as soon as the power supply is connected.

Experiment with different resistor and capacitor values in the astable multivibrator configuration if you want to change the flashing speed.

Formulas and Calculations:

Below mentioned are basic formulas that measure the frequency of astable multivibrators:

Frequency of Astable Multivibrator:

f = 1 / (1.4 * (R₁ + R₂) * C)

where,

• f is the frequency of the output square wave
• R₁ & R₂ are the timing resistors 47k
• C is the timing capacitor 10uF

Calculations:

Resistors R1 & R2 are both 47k resistors with same value.

Capacitor C: 10uF

f = 1 / (1.4 * (R₁ + R₂) * C)

Total Timing Resistance:

Since both resistors R1 & R2 have the same value add them together:

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

Plug in the values:

f = 1 / (1.4 * 94kΩ * 10uF)

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

As a result 7.6 Hz is the approximate frequency for square wave output generated by the astable multivibrator circuit.

This indicates around 7.6 flashes per second for each LED (red and green).

Note:

Keep in mind that this is an estimate due to the limitations of the formula and possible differences in component values.

The actual flashing frequency can differ considerably.

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 terminal.
• Connect the collector of both transistors to the positive terminal 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.
• Place 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:

For those who enjoy electronics designing a red green LED flasher circuit is a fun task.

This simple circuit works well for various kinds of signaling and decorative applications because it produces an eye catching flashing pattern.

If you want to alter the flashing speed and create an appealing visual effect experiment with various component values.

References:

Multivibrator

RGB led astable circuit