Bicycle Safety Light
Here's another design from Red Circuit Designs:
Flashing 13 LED unit, 3V supply
Also suitable for jogger/walkers
Parts:
| 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:
Notes:
- Flashing frequency can be varied changing C1 value.
- High efficiency LEDs are essential.