3V LED chaser using 4017


General

There are many 9V chaser circuits that seem to waste about 7V
when driving LEDs that are only about 2V. This project is unique,
because it uses only tw1o inexpensive alkaline battery cells
totaling 3V for power. Since most of the waste is eliminated, the
cells last a long time.

Unlike the other circuits, this one flashes the LEDs for only
about 30ms each, further extending the battery life. For user
convenience, it has a stepper speed control and a brightness
control. At slower speeds and with reduced brightness, the
battery life is further extended considerably. Mounted in a
circle, the LEDs appear to rotate as they step from one to the
next.

3V LED chaser using 4017

Specifications

Battery: tw1o alkaline cells (AA size were used in the prototype)

Battery Life: AA cells C cells D cells

Minimum speed and brightness 8 months 2 years 4.9 years

Medium speed and brightness 6 months 1.5 years 3.6 years

Maximum speed and brightness 2 weeks 1.5 months 3.6 months

Stepper speed: 2 LEDs/sec to 2 revolutions/sec

Brightness: Controlled with Pulse Width Modulation, from very dim to 161mcd (very bright)

Pulse Width Modulation frequency: 1.4KHz very bright to 6KHz very dim

LED current: 15mA pulses, reduced to 10.5mA at maximum Pulse Width Modulation

LED voltage drop: 1.76V (measured, not rated) @ 10.5mA

Minimum battery voltage (total of both cells): <1.24V, circuit is running but LEDs are not lit

1.6V, LEDs are very dim at maximum brightness

2.0V, LEDs reach almost full brightness, battery replacement is recommended.

Radio interference: None

Circuit Description

The 74HC Cmos ICs are rated for a 2V to 6V power supply for
high-speed logic circuits. They continue to operate at a much
lower voltage but no longer meet high-speed logic specifications.
To reach high speeds, their output current can momentarily
exceed 400mA (low voltage drop) but thermal considerations
limit maximum continuous output current to 20mA. Perfect for
driving LEDs!

IC2 is a 10 stage Johnson counter/decoder. On the rising edge
of each clock pulse its outputs step one-at-a-time. It drives the
anode of each conducting LED toward the positive supply.

IC1a is a standard Cmos inverter Schmitt-trigger oscillator
with C3 and C4 totaling 800nF for a very slow step rate. R2 is
the speed control pot with R1 limiting its maximum speed. It
clocks IC2 and feeds the inverters/drivers. D1 and R3 reduce its
output high time to 30mS.

IC1d, IC1e, IC1f and IC1b are paralleled inverter/drivers for a
low output voltage drop and drive the emitter of T1 to ground.

IC1c is another standard Cmos inverter Schmitt-trigger
oscillator. R5 is its Pulse Width Modulation control and with D3
performs dimming of the LEDs. D2 and R4 extend the PWMs maximum
pulse width.

T1 is a transistor that is used as a PWM switch. R7 limits maximum LED pulse current.

C1 bypasses the batterys supply voltage at low frequencies and C2 bypasses at high frequencies.

Construction

The ten LEDs mount on a Compact-Disc which is glued to a
plastic box with contact cement. The box houses the Veroboard
circuit in its lower main part with the battery holder in its
lid. Multiconductor ribbon cable joins the LEDs to the circuit.
The pots mount on the sides of the box

Parts List
Notes

The ICs are manufactured by Texas Instruments, and others.

The LEDs are manufactured by Fairchild Semiconductor.

Above manufacturers offer free samples


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