How to build Bicycle Back Safety Light Circuit Schematic

Description

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.

Circuit diagram:

Parts:

• R1 = 10K
• R2 = 100K
• R3 = 10R
• R4 = 10R
• R5 = 10R
• R6 = 10R
• R7 = 10R
• R8 = 10R
• R9 = 100K
• R10 = 100K
• R11 = 10R
• R16 = 10R
• R17 = 150R
• C1 = 1μF-63V
• C2 = 10nF-63V
• C3 = 100μF-25V
• B1 = 3V Battery (2 AA 1.5V Cells in series)
• SW1 = SPST Slider Switch
• D1-D13 = Red LEDs 5mm. or bigger, high efficiency
• IC1-IC2 = 7555 or TS555CN CMos Timer IC

LED arrangement:

Notes:

• Flashing frequency can be varied changing C1 value.
• High efficiency LEDs are essential.

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