Bike Turning Signal Circuit

We know the use of bike indicators. These are used to indicate left turn or right turn. Have you ever tried to design bike turning indicators. This article explains you how to design these bike turning indicators.

Bike Turning Signal Circuit Principle:

The objective of this circuit is to indicate left or right turn for bike/vehicle. Two identical circuits are needed, one is for left and the other is for right. The main heart of this circuit is 555 timer. Here, this 555 timer acts as an astable multi vibrator. It generates the pulse signal with variable width. Using this variable width of the pulse, we can set different time delays for the LEDs (ON and OFF for LEDs).

The circuit consists of two 47k resistors, which are connected to 555 timer and these are used to set the time delay for LEDs. 1n4148 signal diode is connected in reverse bias at the output to maintain constant current at the output. BC547 (NPN) Transistor switches the LED’s ON and OFF based on the base currents. 330 ohm resistors are used to drop the voltage otherwise LEDs may get damaged. Here we can vary the time width of output pulse by varying the resistance or capacitance value.

Bike Turning Signal Circuit Diagram:

Bike Turning Signal Circuit Diagram

Circuit Components:

• Resistors       –  3 (47 k ohm)
• Resistors       –  5 (10 k ohm)
• Resistors       -5 (330 ohm)
• Capacitors    – 2 (100uF)
• Transistors   – 5 (BC547)
• LED’s              – 10 (5 mm)
• IC                    – 1 (NE555)
• Diodes           – 2 (1n4148)
• Battery          – 1 (12V)
• wires

Bike Turning Signal Indicator Circuit Design:

In this circuit, 555 timer produces pulse signal with variable width. The pulse width is varied by varying resistance or capacitance value (R2, R1). 2 and 6 pins are shorted to allow triggering after every timing cycle. Fourth pin is reset, it is shorted with VCC (8^th pin) to avoid sudden resets. 7^th pin is discharging pin, it is connected to 6^th pin through a 47k resistor. The below figure explains you the operation of 555 timer. In this circuit capacitor C charges through resistors Ra and Rb. Now because of internal op-amps, capacitor C discharges through resistor Rb. 555 timer internally consist of 2 operational amplifiers, one D flip flop and one NPN transistor.

555 Timer in Astable Mode

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

T = T_HIGH + T_LOW = 0.693 (R_A+ 2R_B) C

 Frequency of the pulse is given as

f = 1/T = 1.44/ (R_A+ 2R_B)C

percentage of duty cycle is given as

% duty cycle, D = t_c / T * 100 = (R_A + R_B) / (R_A + 2R_B) * 100

The obtained pulse from the 555 timer is applied to the transistors to switch the LEDs ON and OFF with some delay. Here the operating voltage of LEDs is around 2 to 3v but from battery, we get 12v supply. So, we need to drop the remaining voltage. To drop this voltage, we are using resistors in series with LEDs. 

How to Operate the Circuit?

• Initially feed 12v power supply to the circuit.
• Now observe the LED’s they will glow with some delay.
• If you want, set the different time delays for LEDs, and then vary the resistance or capacitance value.
• Now you can see the change in time delay.
• By varying the capacitance value also you can see the in time delay of LEDs.

  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.