Flashing 13 LED unit, 3V supply
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)
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.
- Flashing frequency can be varied changing C1 value.
- High efficiency LEDs are essential.