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.
The Seven Segments Display
Many years ago before the LCD (Liquid Crystal Display) come into the arena, the seven segments display is the main player; it’s so popular and its use in almost everything not just to display the numeric value but also a character as well, such as my old Multitech Zilog Z80 microprocessor teaching board to run the BASIC language interpreter bellow:
From the above picture you could see how complex the circuit was on those days; the circuit consists of separate IC such as 8-bit microprocessor (Zilog Z80), counter timer circuit (CTC), 4K EPROM (Erasable Programmable ROM, this ROM type can be erased only by exposing it to the UV lamp) for the firmware (the board basic I/O function and BASIC language interpreter), 2K RAM for the program and the I/O controller. Thanks to today technology this complex circuit is already put into single chip known as the microcontroller and we don’t have to use this UV lamp to erase the program anymore (you must be laugh right know, but on those days that’s the only way to do it) but what remain the same is; we still use this seven segments display, mostly for displaying the numeric value.
Displaying the seven segments is just a matter of applying the correct forward bias voltage to each of the LED’s segment in the seven segments package; for example if we want to show the digit “3” than we have to apply the forward bias voltage on each of the A, B, C, D and G LED segments. The segment pins out is vary among the types and the brands, therefore you have to find out the correct pins for each segments and the common pin as well before you can start to use it.
The Room’s Temperature Project
Our room’s temperature project is use 4 seven segments display for displaying the room’s temperature. The heart of this room’s temperature project is the 8-bit 28 pins midrange Microchip PIC16F886 microcontroller (for those with the Atmel AVR background this microcontroller is comparable to the AVR ATMega8 or ATMega88 microcontroller families). The following is the complete schematic design for this project:
The designed I’ve made here not solely to show the room’s temperature with the seven segments, but it serve as the good learning tools as well, as we will explore the PIC 16F886 features such as ADC (Analog to Digital Converter), PWM (Pulse Width Modulation) and the timer counter capabilities in one shoot. Ok now lets fasten your seat belt as we will run through the design concept here.
For more detail: Seven Segment Display Thermometer with PIC Microcontroller
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