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Automatic Bike Turning Indicator Schematic Circuit Diagram

Creating an automatic bike turning indicator system using a commercially available microcontroller (MCU) can be both costly and challenging to program. However, here we present a cost-effective and straightforward circuit that you can assemble on your own. This circuit serves the purpose of signaling left or right turns for a bicycle or a two-wheeler. You’ll need two identical circuits, one for indicating left turns and the other for right turns. The author’s prototype is depicted in Figure 1, while Figure 2 displays the accelerometer sensor employed in this project.

Automatic Bike Turning Indicator Schematic Circuit Diagram 1

Automatic Bike Turning Indicator Schematic Circuit Diagram 2

Circuit and working for Automatic Bike Turn Indicator

Circuit diagram of the bike turn indicator is shown in Fig. 3. The circuit consists of ADXL335 accelerometer sensor, voltage regulator 7805 (IC1), LM393 comparator IC (IC2), two NE555 timer ICs (IC3 and IC4) and a few other components.

Automatic Bike Turning Indicator Schematic Circuit Diagram 3

ADXL335 is a compact, slim, low-power, and comprehensive 3-axis accelerometer with voltage outputs that are pre-conditioned. However, for this project, only the Y-axis of the ADXL335 is employed. This device is designed to measure acceleration and operates within a minimum full-scale range of ±3 volts. It has the capability to detect both static acceleration caused by gravity in tilt-sensing applications and dynamic acceleration resulting from various forms of motion, shock, or vibration.

The dual comparator LM393 is an 8-pin integrated circuit (IC) where pins 1, 2, and 3 constitute one comparator, while pins 5, 6, and 7 form another comparator. These two comparators are responsible for monitoring the signals indicating left and right turns. Additionally, two NE555 timer ICs (IC3 and IC4), configured as monostable multivibrators, are used—one for the left-turn signal and the other for the right-turn signal. To power the circuit, a 9V-12V battery is converted to +5V DC through the voltage regulator IC (IC1).

Left signal

When the bike handle is turned to the left, it generates a tilt angle output voltage ranging from 1.2V to 2.6V. In this configuration, the inverting terminal (pin 2) of IC2 is linked to the Y signal from the ADXL335 sensor, while the non-inverting terminal (pin 3) is connected to a preset resistor (VR1). The left tilt angle signal is then obtained from pin 1 of IC2.

To establish a reference voltage of 2.2V at pin 3, preset resistor VR1 is used. Initially, when the bike handle turns 90 degrees to the right, the comparator voltage level at pin 3 remains at 2.2V, while at pin 2, it’s approximately 2V. Consequently, the comparator outputs a high (5V) state. This high output is directed to pin 2 of IC3, causing the output of IC3 to be low.

Whenever the bike handle is turned to the left, the voltage at pin 2 of IC2 becomes 2.6V, leading to a low output at pin 1. This low signal is connected to trigger pin 2 of IC3, which, in turn, results in a high output at pin 3 of IC3. Transistor T1 then conducts, causing LED1 to illuminate. The monostable IC3 generates a pulse width as determined by the following formula:

t=1.1×R2×C4 seconds

Right signal

When the bike handle moves towards right direction, it gives tilt angle output in the form of 2.6V to 1.2V voltage (decreases from high to low). Inverting terminal pin 6 of IC2 is connected to preset (VR2), and non-inverting terminal pin 5 to ADXL335 sensor Y signal.

Set reference voltage at the inverting terminal to 1.6V using VR2. Initially, when bike handle turns 90 degrees, voltage levels at pin 6 will be 1.6V and at pin 5 will be 2V. This means that comparator output will be in high (5V) state. This output is fed to pin 2 of IC4, which makes its output pin 3 low.

Whenever the bike handle turns right, voltage level at pin 5 of IC2 will be 1.2V. This is lower than the reference voltage (1.6V) at pin 6. This makes output pin 7 of IC3 low. The low output triggers monostable multi-vibrator IC4. This makes output pin 3 of IC4 high, transistor T2 to conduct and LED2 to glow.

Monostable output pulse is given by the following relationship:

t=1.1×R3×C7 seconds

Construction and testing

The PCB layout for the Automatic bike turn indicator is shown in Fig. 4 and its components layout in Fig. 5. Assemble the components on the PCB as per the circuit diagram.

Automatic Bike Turning Indicator Schematic Circuit Diagram 5

Automatic Bike Turning Indicator Schematic Circuit Diagram 6

Connect a 9V-12V power supply to the circuit. Adjust voltages at pins 3 and 6 of IC2. The bike signal turn indicator is ready for use.


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