Electronic bicycle directional light circuit using cheap components

This is an electronic bicycle directional light circuit using cheap components and is a good alternative to many commercial versions on the market. The circuit works very differently and is easy to operate.

The bicycle direction indicator circuit operates from a 9VPP3 (alkaline) battery and is basically a set of two independent free-running oscillators (astable multivibrators) built around four low-power transistors and some passive components. Two square wave oscillators (one built around T1 and T2, the other around T3 and T4) drive four red LEDs (LED1 and LED2, and LED5 and LED6 respectively) which flash to indicate the direction of the turn. Additional permanently lit LEDs (LED3 and LED4) are used to indicate the working status.

How Bicycle Turn Signal Lights Work

When switch S1 is flipped to the "on" position, the DC power from the battery is extended to the oscillator circuit formed by transistors T1 and T2. Now the left oscillator starts to oscillate and the left front (FL) and left rear (RL) visual indicators start flashing at a rate determined by timing capacitors C1 and C2. Resistors R2 and R3 limit the operating current of the LEDs (LED1 and LED2). At the same time, the green LED (LED3) starts to glow, indicating the current direction status.

When switch S2 is flipped to the "on" position, a similar action occurs in the next oscillator circuit built around transistors T3 and T4. The right front (FR) and right rear (RR) indicators begin to flash, and the green LED (LED4) turns on, indicating the directional status.

Switch S3 is used for emergency indication. When it is flipped to the "on" position, both oscillators get power through diodes D1 and D2. Therefore, LED1 to LED6 start working simultaneously. In this case, all LEDs flash except LED3 and LED4 which glow steadily.

Bicycle turn signal assembly

After assembling the circuit on a general purpose PCB, enclose it in a suitable cabinet as shown in the following figure and then mount it on the handlebars of the bicycle, preferably at the mechanical center point.

Connect the switch S1 on the left, S2 on the right and the emergency switch S3 in the middle of the main unit. Now place this main unit on top of the handlebars and make the necessary interconnections using flexible wires. Connect the front indicators (LED1 and LED5) to the left and right sides of the handlebars and similarly the rear indicators (LED2 and LED6) can be mounted on the frame of the bike.

For the direction indicator you can use the direction symbol and place it in the center of the handle, check out the picture above for reference.