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A 7-Segment display is made up of seven rectangular LEDs arranged in a figure of 8 pattern. By lighting up the LEDs in the right order it is possible to get them to display the numbers 0 to 9.

 

An integrated circuit (IC) is available called a 4026 which allows you to build a counter that will increase its value every time it receives a clock pulse. This pulse could come from a switch of some kind or the output of an other circuit, like an astable circuit for example.

What the inputs and outputs do

 

CE = Chip Enable

This must be connected to 0V to turn the 4026 on.

 

DE = Device Enable

This must be connected to +V to turn the 4026 on.

 

EO = Enable Output

This must be connected to +V to turn on the LED display.

 

R = Reset

When this input has a logic 1 connected the display will be reset to 0.

 

> = Clock Input

Each time a logic pulse is received by this input the display will increase its value by 1.

 

a, b, c, d, e, f, g = LED outputs

Each LED segment is connected up to the each of these outputs. The 220R resistors must be included to limit the current flowing through the LEDs, this prevents them from becoming damaged.

 

Power

Although it isn’t shown in the diagram the 4026 chip also has 0V and +V inputs.

a
b
c
d
e
f
g
4026 7-Segment Counter

Oops! Can you spot what is wrong with this?