Bicycle back Safety Light

Flashing 13 LED unit, 3V supply

Also suitable for jogger/walkers

Circuit diagram:

Bicycle safety light


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 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.

LED arrangement:

LED arrangement