Inserting two 1-MO resistors, R1 and R2, in the output stage of one of the circuit`s inverters limits the current needed by the oscillator tone more than a few pA. This circuit includes a CD4007 package, which has three CMOS inverters. It forms a standard three-inverter oscillator. Resistors R1 and R2, in series with separate drains on inverter pins 8 and 13, limit the oscillator`s supply current. Capacitor C1 and resistors R5 set the off time of the oscillator, C1; R6 sets the on time. A VN10KM small-power FET, currentlimited by R4, drives two HLMP-3300 LEDs.
Three-year-led-flasher - schematic

The LEDs consume about 20 mA for 1 ms. Their average current determines battery life. Since the LEDs in the circuit flash at 1 Hz, the average current drain is about 1/1000 of 20 mA, or 20 p.A. A 9-V battery should last about three years at the current drain-essentially the shelf life of an alkaline battery.

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