Mechatronics

Mechatronics

Abstract

The seven segment display is one of the most popular numeric displays used in many microcontroller applications because it's cheap, robust and reliable. The seven segments actually consists of 8 LED (Light Emitting Diode) and it's come with various sizes suitable for various numeric display application such as digital clock, counter, thermometer, humidity, etc. On this project we are going to show you how to drive this type of display and this time we will use the Microchip PIC16F886 microcontroller to display the room's temperature both in Centigrade and Fahrenheit scale.

Procedures

Seven segment displays are very common for electronic product to display numerical output. Many common devices like calculators, watches, electronic weighing scales, ovens and many other household items use them. You must have also seen lifts display the current floor numbers in seven segment displays. They are primarily used to display decimal numbers but they can also display a few alphabets and other characters. Many display boards ,advertising boards make use of seven segment LEDs. A seven-segment display is so named because it is divided into seven different segments that can be switched on or off.It has an special arrangement of 7 LED elements to form a rectangular shape using two vertical segments on each side with one horizontal segment on the top, middle, and bottom. By individually turning the segments on or off, numbers from 0 to 9 and some letters can be displayed. Seven segment displays sometime also have an eighth segment to display the decimal point. Therefore, a seven-segment display will require seven outputs from the microcontroller to display a number, and one more output if the decimal point is to be displayed too. The figure shows a seven segment display and the names of the various segments.

The image above shows a four digit seven segment display. These type of displays are widely used to present numerical data to users. Example includes clocks, panel meters, microwave ovens, refrigerators etc. As you can see in a four digit displays there are a total of 4 x 7 = 28 segments (made of leds) so you may think that they will require lots of i/o pins of MCU. But in reality a small trick can greatly reduce the number of i/o pins required.

The trick is to activate only one digit at a time. All the segments of each four digit are connected in parallel and common of each four digit is tried to MCUs i/o port via transistors. That means MCU can select any digit and put the segment data which drives the segments. Only the selected digit will light up. Then next digit is selected and segment data is changed according to the digit that must be shown in that place. Similarly each digit is selected and shown. This is done fast enough that the human I cannot see the movement. We can see all four digit lit at the same time as shown in the figure above.

To display any four digit number, say 1234 on the ...