Week 11 – Seven Segment

Arduino – 7-segment Display
Introduction

An LED or Light Emitting Diode is a solid state optical pn-junction diode which emits light energy in the form of photons. Seven segment display is the most common device used for displaying digits and alphabet. One can see a device in TV shows counting down to ‘0’, these are nothing but seven segments. Use of LEDs in seven segment displays made it more popular.

The binary information can be displayed in the form of decimal using this seven segment display. Its wide range of applications is in microwave ovens, calculators, washing machines, radios, digital clocks etc.
The seven segment displays are made up of either LEDs (Light emitting diode) or LCDs (Liquid crystal display). LED or light emitting diode is P-N junction diode which emits the energy in the form of light, differing from normal P-N junction diode which emits in the form of heat.
Liquid crystal displays (LCD) use the properties of liquid crystal for displaying. LCD will not emit the light directly .These LED’s or LCD are used to display the required numeral or alphabet. Single seven segment or number of segments arranged in an order meets our requirements.
Figure 1 shows a seven segment LED display. As indicated by the diode equivalent circuit on the left, each segment is an individual LED. This is a Common Cathode (CC) display. All of the cathodes (or negative terminals) of the segment LEDs are connected together. 

Working of Seven Segment Display
Seven segment display works, by glowing the required respective LEDS in the numeral. The display is controlled using pins that are left freely. Forward biasing of these pins in a sequence will display the particular numeral or alphabet. Depending on the type of seven segment, the segment pins are applied with logic high or logic zero and in the similar way to the common pins also.
For example to display numeral ‘1’ segments b and c are to be switched on and the remaining segments are required to be switched off. In order to display two digits two seven segments are used.
Interfacing microcontrollers and seven segment displays.
Figure shows a common cathode seven segment display connected to an Arduino Uno single board computer (SBC). You will need a USB-A to B cable to program the Arduino. 

Circuit Diagram

It requires 7 digital I/O pins to drive the segments, 8 if the decimal point is included. 

Breadboard Layout