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The circuit below will flash any LED color with fixed current pulses powered by a
3v battery. It uses a charge pump approach, which routes a constant current
pulse through the LED, regardless of the LED voltage requirement. Using this
approach, white and blue LEDs, which normally require about 3.6v can be flashed
with a 3v battery. With the component values selected, the LED is hit with
15ma current pulses lasting about 10ms every two seconds. This keeps the
average current draw from a 3v battery to about 200uA.
The circuit relies on a cheap
74HC14 hex Schmitt trigger inverter IC. One inverter forms a pulse
generating oscillator. Other inverters are ganged together to increase the
drive current. A two transistor circuit forms a constant sinking current
controller.
Click on Drawing Below to view PDF version of Schematic
