Circuit is basically a "gated" blocking oscillator (joule thief). IC1 CD4001 requires 3V and will not run from 1.5V (AA cell) when first connected. By shorting the header pins 1-2 momentarily, circuit oscillates and flyback voltage pulses (around 100KHz) appear at collector of transistor Q1. These pulses are rectified by LED and charge capacitor C3 while at the same time light is emitted by LED. Now, CD4001 is powered from C3 with adequate supply voltage, and produces short pulses (1.5mS) from monostable IC1-C & IC1-D at a rate of 1Hz (header pins disconnected) These pulses enable the oscillator during 1.5mS which charges C3 and lights LED at the same time. During the OFF time, voltage of C3 drops feeding CD4001. This circuit is optimized for extremely low current drain ( < 50uA average with new 1.5V cell ). A good quality AA alkaline cell can deliver up to 3000mAH. At 50uA that gives 60,000 hours or 2500 days or nearly 7 years. As the cell voltage decreases with time so does the current drain. This will extend the operation time even more, until the cell is depleted or leaks.
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