Displays are used to show the output of a process or status of equipment or monitoring the status of the process.
The simplest display used in an electronic equipment is two lead LED, one for anode(+ve) and another for cathode(-ve). The LED indicator is simplest and cheapest display system for monitoring the process, available in multiple colours, which makes the display of status more easier. The LEDs works between 1.8 VDC to 3.5VDC, which depends on emitting colour and manufacturer . The current capacity depends on its size (in diameter) and wattage.
for more description on LEDs click here
Seven Segment LED Displays:
Next comes the Seven Segment Display, which is a rectangular block having seven long rectangular LEDs in 8 format. The Seven segment display is normally used to show numerics from 0 to 9 by switching ON and OFF particular LEDs.
Sometimes some Alphabet are also displayed using Seven Segment Display.
Connecting pins for each LED (segment) are available at the back side of the Seven Segment Display, with one or two common pins for all seven segments. The common pin may be connected to positive (or negative) DC power supply and other pins of seven segments may be connected to negative (or positive).
For Common Anode (CA) Seven Segment Display, the common pin(s) should be connected to Positive DC power supply and each segment pin should be connected to negative power supply to glow the particular segment (or LED).
Similarly, for Common Cathode (CC) Seven Segment Display, the common pin(s) should be connected to Negative DC power supply and each segment pin should be connected to positive power supply to glow the particular segment (or LED).
In general, Seven Segment Displays may glow in Red or Green colour in various sizes like 0.5", 1", 2.5", 4" etc. Now-a-days Seven Segment Displays are available in RGB colours also.
All the Seven Segments are named as a, b, c, d, e, f, g and one more pin is used to glow dot on the right bottom side of the rectangle. The pin connections depends on the model , size and manufacturer.
Connections and identification of seven segment are shown here for Seven Segment Display with top and bottom pins.
The seven segment displays are also available in multiple displays in one block. This will reduce the wiring and number of pins to control the display. For continuous display, each segment of particular display has to be selected sequentially, which may be managed by a micro-controller.
A 4-in-1 seven segment block is shown here. similarly, 2-in-1 and 3-in-1 are also available.
Sixteen Segment Alpha-Numeric LED Display:
The 16 Segment LED display is similar to Seven Segment Display, except it can display all Alphabets and Numerics.
The main difference is, the three horizontal segments ( a, g and d ) are made in two parts , two vertical and four inclined segments are added in between.
LED Bar Graph:
LED Bar Graph is a rectangular block with 10 number of LEDs arranged in a row. The connecting pins (10 anode + 10 cathode) are available at the back side of the block as shown in the figure. They are available in Red or Green or Blue or Yellow or Amber or RGB colored LEDs
LED Matrix Array:
64 LEDs are arranged in 8 X 8 matrix format in a square block. By selecting pins at the back side of the block, required LEDs in combination of 8 rows and 8 columns may glow.
The LEDs may glow in Red or Green or Blue colour. Now-a-days, RGB colours are also available. In this case, each LED may glow in combination of colours. So, the LED matrix is very useful to display pictures or graphical output.
It is very difficult to select each LED out of 64 LEDs. So a separate display controller IC (MAX7219) is used for the purpose. The IC has serial data input and serial data output pins, which may controlled by a micro-controller.
A display module with the IC (MAX7219) is readily available in the market. Some modules have two or four display blocks on single PCB and simple serial data control system.
Any number of LED matrix modules may be connected in series and are to be controlled by a micro-controller (or similar circuit).
A readily available 4-in-1 LED matrix module is shown here, which has input pins one side and output pins on another side to connect further / next modules in series.
The LCD (Liquid Crystal Display) is highly used text display in micro-controller projects, which is cheaper and easily available. The text may be displayed in the following ranges:
1 Row x 16 Columns
2 Rows x 16 Columns
4 Rows x 16 Columns
4 Rows x 20 Columns
The LCD may controlled by 16 pins. The data may be sent by 8 bit (byte) or 4 bit (nibble), which should be selected by sending specific codes after power on. The contrast of the display is controlled at pin-3 of LCD, through a trim-pot connected between 5VDC and ground.
The GLCD (Graphical Liquid Crystal Display) has good viewing size of pixel size (0.48mm x 0.48 mm) and screen area (66mm X33mm approx.).
The screen is logically divided into two panes as 64X64 pixels on left side and 64X64 pixels on right side, which makes 128X64 pixels in total. The left side pane is selected using CS1 pin and similarly right side pane is selected using CS2 pin.
The data and command to GLCD is transmitted in 8 bit format by selecting RS pin setting high/low. The contrast of the display is controlled at pin-3 of GLCD, through a trim-pot connected between -10VDC ( available at pin 18 of GLCD) and ground.
OLED ( Organic Light Emitting Diode ) is available in very small size with graphical display support, which consumes very less power and displays sharp image.
The input pins contains either I2C (TWI) or SPI (or both) interface with two power supply pins. The display size and display colour(s) varies as per specification. The OLED shown here are highly used in the DIY projects.
TFT-LCD (Thin Film Transistor Liquid Crystal Display) has smaller and sharper pixel than normal LCD display and consumes lesser power. TFT-LCD can display an image or text in colour.
Some TFT-LCD modules have touch sensitivity with stylus and/or Micro-SD card slot. Most of the small size (upto 3.5 inch) TFT-LCD modules have pins, which are compatible (suitable) for Arduino Uno / Arduino Meaga boards. The higher sized TFT-LCD modules may have various signal input pins and slots like, USB, VGA, HDMI etc.
Other display systems like AMOLED (Active-Matrix Organic Light-Emitting Diode), SAMOLED (Super Active-Matrix Organic Light-Emitting Diode), QLED (Quantum dot Light Emitting Diode) are new technologies emerging in the market. But, proper interfacing system for DIY is not available right now. In future, some more new technologies in display system is expected with high quality and low power consumption at affordable price.