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Bike Turning Signal Circuit

In this project, I’ll guide you through the process of creating a straightforward Bike Turning Signal Circuit. We’ll be using a 555 Timer IC, a pair of LEDs, and several readily accessible components.

Bike Turning Signal Circuit


  • Introduction
  • Bike Turning Signal Circuit Principle
  • Bike Turning Signal Circuit Diagram
  • Circuit Components
  • Bike Turning Signal Indicator Circuit Design
  • How to Operate the Circuit?
  • Applications of Bike Turning Signal Indicator Circuit


Turn Indicator Lights, officially known as Directional Indicators, or informally as Blinkers or Flashers, are an essential feature in all vehicles, including motorcycles and automobiles. They serve the purpose of signaling to other drivers our intent to turn either left or right. Manufacturers must comply with various regulations and standards when designing and incorporating Turn Lights into vehicles.

Bike Turning Signals are employed to communicate the intention of making a left or right turn to fellow road users. Have you ever tried your hand at constructing a set of bicycle turn indicators? This article will provide guidance on creating these turn signals for bicycles.

Bike Turning Signal Circuit Principle

The objective of this circuit is to provide directional indications for left or right turns in vehicles, such as bikes or cars. Central to this circuit is the 555 Timer IC, functioning as an Astable multivibrator. It generates a pulse signal with a variable width, allowing us to configure different time delays for the LEDs by adjusting their ON and OFF durations.

Two pivotal resistors, namely 100K and 470K, are connected to the 555 timer, serving to establish the time delay for the LEDs within the circuit. A Slide Switch is employed to direct the 555 Timer IC’s output towards either the LEFT or RIGHT indication LED.

To ensure a consistent current flow at the output, a 1n4148 signal diode is connected in reverse bias. The BC547 (NPN) Transistor controls the LEDs’ activation and deactivation based on the base currents. It is essential to include 330-ohm resistors to lower the voltage, as LEDs could otherwise be at risk of damage. By altering the resistance or capacitance values, the pulse’s temporal width in the output can be adjusted accordingly.

Bike Turning Signal Circuit Diagram

Circuit Components

  • Resistor 180Ω
  • Resistor 100KΩ
  • Resistor 470KΩ
  • Capacitor 1µF
  • 555 Timer IC
  • LEDs – 2
  • Diodes (1N4007) – 2
  • SPDT Slide Switch
  • 9V Battery
  • Connecting Wires
  • Breadboard

Bike Turning Signal Indicator Circuit Design

In this circuit, the 555 timer generates a pulse signal with adjustable width. Modifying the resistance or capacitance values (such as 100K, 470K, or 1F) allows for changes in the pulse width. To enable triggering after each timing cycle, pins 2 and 6 are connected.

To prevent inadvertent resets, pin 4 is connected to VCC (8th pin). The 7th pin, which serves as the discharge pin, is linked to the 6th pin via a 470K resistor. The 555 timer’s internal structure consists of two operational amplifiers, one D flip-flop, and one NPN transistor. In this configuration, capacitor C is charged through resistors RA and RB. Subsequently, capacitor C discharges via resistor RB due to the internal op-amps. The diagram below illustrates the internal components of the 555 timer.

In the above circuit, the pulse is generated at the 3rd pin of the 555 timer. By varying the values of RA, RB or C, we can vary the pulse width. The total time period of the pulse is given as

T = THIGH + TLOW = 0.693 (RA+ 2RB) C

 Frequency of the pulse is given as

f = 1/T = 1.44/ (RA+ 2RB)C

percentage of duty cycle is given as

% duty cycle, D = t/ T * 100 = (RA + RB) / (RA + 2RB) * 100

The output pulse generated by the 555 timer is routed to the LEDs via the slide switch, allowing them to be illuminated with a delay. While the LEDs typically operate at an operational voltage of approximately 2 to 3 volts, our power source provides 9 volts. To adjust the voltage to the appropriate level, we incorporate resistors in series with the LEDs.

How to Operate the Circuit?

  • Initially, supply the circuit with a 9V power supply.
  • When you slide the switch to the left, the LEFT Indicator LED will begin to blink with a slight delay.
  • The RIGHT Indicator LED will blink if you slide the switch to the right position.
  • Both LEDs will be turned off if you slide the switch to the centre position.
  • Set alternative LED time delays if desired, then change the resistance or capacitance value.
  • You can now observe the difference in time delay.
  • You can see the in time delay of LEDs by altering the capacitance value.

NOTE: Since this is a demonstration, I have used only one LED per channel (LEFT and RIGHT). But if you want to integrate several LEDs per channel, you can do that with the help of a Transistor on each channel and sufficient power supply.

Applications of Bike Turning Signal Indicator Circuit

  • It is used to indicate left turn or right turn for a motor bike or vehicle.
  • We can also use this circuit as an LED knight rider circuit.
  • We can give it as a gift for the children.

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