LED bar graph indicator

INTRODUCTION

led bar graphs are seen in many electronic systems to just give a visual interpretation of magnitude for example-

1. In arcade games to indicate how much hard the hammer was hit.

2. In VU meters to indicate volume intensity.

The applications are vast as led bar graphs are used to indicate the magnitude of any physical parameter like pressure, temperature, light intensity as long as there is a transducer available for that physical quantity.

CIRCUIT DIAGRAM AND EXPLANATION

CONSTRUCTION

This is the circuit diagram of led bar graph which I have made using IC 4017 and two timer IC 555 .

IC 4017 is a ring counter IC and its function is to light led sequentially (one after the other) from Q0 to Q9 .The clock pulse fed to this IC decides the speed of scanning from Q0 to Q9 .

Two timer IC 555 are used in astable mode to provide clock pulses.

look at above circuit diagram , IC to left provides fixed clock pulse to clock pin and other provides pulses to MR( reset) pin the whose frequency is variable by 10K potentiometer.

10 leds are connected at the output pins of 4017 with 220 ohm resistor in series.

WORKING:-

Our persistence of vision and the reset function of 4017 plays a major role in this circuit operation.

Giving a reset pulse starts the cycle from Q0 to Q9 . That means at any instant of time while the cycle is running if you give a reset pulse ,the cycle will start again from Q0 . Now imagine what would happen if we give the reset pulse again and again at high frequency.

as the cycle will never exceed Q0 . Its like accelerating and breaking at same time.

Lowering the reset frequency little bit will allow cycle to exceed Q0.

Now Q0 and Q1 both will be visible .This tells us that the reset pulse on time is two clock pulse wide.

The reset on time must be maximum 10 clock cycles wide because we have 10 output and minimum 1 clock cycle wide .That's the reason why I have kept the clock frequency higher than the reset frequency.

According to calculation

clock freq > 20 (reset freq)

One more reason to keep the clock frequency high is to achieve persistence of vision so that it gives an illusion that all leds are on at same time with constant brightness. Its better to keep the clock frequency in KHz .