How to build Bicycle back Safety Light

Flashing 13 LED unit, 3V supply
Also suitable for jogger/walkers

Circuit diagram

R1 10K 1/4W Resistor
R2,R9,R10 100K 1/4W Resistors
R3-R8,R11-R16 10R 1/4W Resistors
R17 150R 1/4W Resistor
C1 1µF 63V Polyester Capacitor
C2 10nF 63V Polyester Capacitor
C3 100µF 25V Electrolytic Capacitor
D1-D13 Red LEDs 5mm. or bigger, high efficiency
IC1,IC2 7555 or TS555CN CMos Timer IC
SW1 SPST Slider Switch
B1 3V Battery (2 AA 1.5V Cells in series)

Device purpose:
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.

Circuit operation:
IC1 is a CMos version of the 555 IC wired as an astable multivibrator generating a 50% duty-cycle square wave at approx. 4Hz frequency. At 3V supply, 555 output (pin 3) sinking current operation is far better than sourcing, then LED D1-D6 are connected to positive supply. 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.

LED arrangement:

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

Author: RED Free Circuit Designs

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