how to build bicycle back safety light

Description: This circuit is designed to provide a clearly visible light using 13 high-efficiency flashing LEDs arranged in a pseudo-rotating order. Due to its low voltage, low battery drain operation, and compact size, the device is suitable for mounting on bicycles as a backlight or for use by joggers and walkers. IC1 is a CMOS version of the 555 integrated circuit, configured as an astable multivibrator generating a 50% duty-cycle square wave at approximately 4 Hz frequency. At a 3V supply, the 555 output (pin 3) is more effective in sinking current than sourcing it, leading to LEDs D1-D6 being connected to the positive supply rail. To achieve an alternating flashing operation, a second 555 IC is included, functioning as a trigger and inverter to drive LEDs D7-D12. LED D13 is permanently illuminated. The LEDs are arranged in two series displays, with a central LED that is always on. This configuration, along with the alternating flashing of the two series of LEDs, creates a pseudo-rotating effect.

The circuit employs a dual 555 timer configuration to achieve its intended functionality. The first 555 timer (IC1) operates in astable mode, generating a continuous square wave signal at a frequency of approximately 4 Hz. This frequency is suitable for creating a visually appealing light effect without being overly distracting. The duty cycle of 50% ensures that the LEDs are on for equal durations, contributing to a balanced light output.

The output from the first 555 timer is connected to the first set of LEDs (D1-D6), which are arranged in a series to enhance visibility. The choice of high-efficiency LEDs ensures that the circuit operates effectively at low voltages, making it ideal for battery-powered applications. The design consideration of sinking current rather than sourcing it allows for a more efficient use of the 3V supply, minimizing power consumption.

The second 555 timer serves as a trigger and inverter, controlling the second set of LEDs (D7-D12). This arrangement allows for the alternate flashing of the two series of LEDs, creating a dynamic light display that simulates rotation. The central LED (D13), which remains constantly illuminated, acts as a reference point, enhancing the visual effect of the pseudo-rotation.

This circuit is particularly advantageous for outdoor applications, such as bicycle lighting or for joggers and walkers, due to its compact size and low power requirements. The design not only ensures safety through visibility but also provides an engaging visual effect that can attract attention in low-light conditions.This circuit has been designed to provide a clearly visible light, formed by 13 high efficiency flashing LEDs arranged in a pseudo-rotating order. Due to low voltage, low drain battery operation and small size, the device is suitable for mounting on bicycles as a back light, or to put on by jogger/walkers.

IC1 is a CMos version of the 555 IC wired as an astable multivibrator generating a 50% duty-cycle square wave at about 4Hz frequency. At 3V supply, 555 output (pin 3) sinking current operation is far better than sourcing, then LEDs D1-D6 are connected to the positive supply rail. In order to obtain an alternate flashing operation, a second 555 IC is provided, acting as a trigger plus inverter and driving LEDs D7-D12.

D13 is permanently on. The LEDs are arranged in a two series display as shown below, with a center LED permanently on. This arrangement and the alternate flashing of the two series of LEDs provide a pseudo-rotating appearance.