This 1.5 volt led fasher runs more than a year on a single 'd" cell
and alternately flashes 2 LEDs at about a 1 second rate. The circuit
employs a 74HC14 CMOS hex inverter that will operate at very low
voltages (less than 1 volt). One section is used as a squarewave
oscillator (pins 1 and 2), while the others are wired to produce
a short 10mS pulse on alternate edges of the square wave so the LEDs
will alternate back and forth.
The output sections each use a
capacitor charge pump to increase the voltage for the LEDs. The circuit
draws an average current of 800uA from the 'D' battery and the LED
peak current is about 40mA with a fresh battery and drops to about
10mA as the battery voltage falls to 1.1 volts. The capacity of
a alkaline 'D' cell is about 12 amp hours with a cutoff voltage
of 1.1 so the circuit should run about 12/.0008 = 15000 hours or
maybe 625 days, but I haven't verified that yet. The idea for this
circuit came from a single 1.5 volt LED flasher by Dave Johnson
that can viewed at
1.5 volt dual LED flasher Circuit Diagram
Author : Bill Bowden
