Tutorial-2 LCD Interfacing with Arduino

Introduction:

The LiquidCrystal library allows to control LCD displays that are compatible with the Hitachi HD44780 driver. A Liquid Crystal Display commonly abbreviated as LCD is basically a display unit built using Liquid Crystal technology. When building real world electronics based projects, need a medium/device to display output values and messages.

The most basic form of electronic display available is 7 Segment display – which has its own limitations. The next best available option is Liquid Crystal Displays which comes in different size specifications. Out of all available LCD modules in market, the most commonly used one is 16×2 LCD Module which can display 32 ASCII characters in 2 lines (16 characters in 1 line). Other commonly used LCD displays are 20×4 Character LCD, Nokia 5110 LCD module, 128×64 Graphical LCD Display and 2.4 inch TFT Touch screen LCD display.

Working of the project:

Firstly Need to enable the header file (‘#include <LiquidCrystal.h>’), this header file has instructions written in it, which enables the user to interface an LCD to UNO. With this header file need not have to send data to LCD bit by bit, this will all be taken care of and don’t have to write a program for sending data or a command to LCD bit by bit and In this LCD each character is displayed in a 5×7 pixel matrix.

After that need to tell the board which type of LCD we are using here. Since have so many different types of LCD (like 20x4, 16x2, 16x1 etc.). Here are going to interface a 16x2 and 20x4 LCD to the UNO so get ‘lcd.begin(16, 2); and ‘lcd.begin(20,4 );. For 16x1 get ‘lcd.begin(16, 1);’.In this instruction, going to tell the board where connected the pins. The pins which are connected need to be represented in order as “RS, En, D4, D5, D6, D7”. These pins are to be represented correctly. Since have connected RS to PIN0 and so on as show in the circuit diagram, we represent the pin number to board as “LiquidCrystal lcd(0, 1, 8, 9, 10, 11);”. The data which needs to be displayed in LCD should be written as “ cd.print("hello, world!");”. With this command the LCD displays ‘hello, world!’.

Table of Content:

1. List of Inventories

1.1 Hardware Requirements

1.2 Software Requirements

1.3 Brief Introduction of component and calculate resistance

2. System Modelling

2.1 Circuit Diagram, Schematic Diagram and PCB Layout

2.2 Source Code Programming

2.2.1 16x2 LCD Interfacing with Arduino

2.2.2 20x4 LCD interfacing with Arduino

2.2.3 Scrolling text display on LCD

2.2.4 Special Character Display on LCD
2.2.5 Demultiplexing of LCD
2.2.6 Design and play the game with Arduino

2.3 How to get .hex file

2.4 Detail explanation of code

1. List of Inventories:

1.1 Hardware:

1. Liquid Crystal Display (16x 2 and 20x4)

2. Jumper wires - 12 (Male to male)

3. Resistor: 65 ohm

4. Potentiometer: 1k ohm

5. Power Supply: 1) 9 to 12 Vdc & <= 1A (For Arduino)

+2) 5 to 9 Vdc (For LCD)

Development Board:

1. Arduino or Genuino UNO

1.2 Software and Library:

1. Arduino Software

1.1 Arduino for MAC OS

1.2 Arduino for Linux OS

1.2.1 For LINUX ARM
1.2.2 For LINUX ARM64
1.2.3 For LINUX 32-bit
1.2.4 For LINUX 54-bit

1.3 Arduino for Windows OS

2. Proteus Software

3. Library

3.1 Arduino Library for Proteus

3.2 Genuino Library for Proteus
3.3 LCD Library for Proteus

1.3 Brief introduction of the components:

1) Arduino UNO

Arduino is a simple to use microcontroller board used in most engineering projects where automation is needed. IO devices like Sensor, modules and many others things can be interfaced with the Arduino board to accomplish a task. Arduino is an open source board which means that all the design specifications, schematics, and software library are available openly for all users. The Arduino board has gained popularity today among many hobbyists because it is friendly and easy to use and can be used to design complex projects. It can be easily programmed using its own software; the Arduino IDE. The nature of the Arduino language is friendly and makes it easy for everyone to develop prototypes and hardware to suit their intended purpose.

2) LCD

The liquid crystal display uses the property of light monitoring of liquid crystal and they do not emit the light directly. The Liquid crystal display is a flat panel display or the electronic visual display. With low information, content the LCD’ s are obtained in the fixed image or the arbitrary image which are displayed or hidden like present words, digits, or 7 segment display. The arbitrary images are made up of large no of small pixels and the element has larger elements.

I. What is a LCD (Liquid Crystal Display)?

A liquid crystal display or LCD draws its definition from its name itself. It is combination of two states of matter, the solid and the liquid. LCD uses a liquid crystal to produce a visible image. Liquid crystal displays are super-thin technology display screen that are generally used in laptop computer screen, TVs, cell phones and portable video games. LCD’s technologies allow displays to be much thinner when compared to cathode ray tube (CRT) technology.Liquid crystal display is composed of several layers which include two polarized panel filters and electrodes. LCD technology is used for displaying the image in some other electronic devices. Light is projected from a lens on a layer of liquid crystal. This combination of colored light with the gray scale image of the crystal (formed as electric current flows through the crystal) forms the colored image. This image is then displayed on the screen.

An LCD is either made up of an active matrix display grid or a passive display grid. Most of the Smartphone’s with LCD display technology uses active matrix display, but some of the older displays still make use of the passive display grid designs. Most of the electronic devices mainly depend on liquid crystal display technology for their display. The liquid has a unique advantage of having low power consumption than the LED or cathode ray tube.Liquid crystal display screen works on the principle of blocking light rather than emitting light. LCD’s requires back-light as they do not emits light by them.

II. How LCD constructed?

LCD Layered Diagram

Simple facts that should be considered while making an LCD:

1. The basic structure of LCD should be controlled by changing the applied current.

2. Must use a polarized light.

3. Liquid crystal should able be to control both of the operation to transmit or can also able to change the polarized light.

As mentioned above that need to take two polarized glass pieces filter in the making of the liquid crystal. The glass which does not have a polarized film on the surface of it must be rubbed with a special polymer which will create microscopic grooves on the surface of the polarized glass filter. The grooves must be in the same direction of the polarized film. Now we have to add a coating of pneumatic liquid phase crystal on one of the polarized filter of the polarized glass. The microscopic channel cause the first layer molecule to align with filter orientation. When the right angle appears at the first layer piece, we should add a second piece of glass with the polarized film. The first filter will be naturally polarized as the light strikes it at the starting stage.

Thus the light travels through each layer and guided on the next with the help of molecule. The molecule tends to change its plane of vibration of the light in order to match their angle. When the light reaches to the far end of the liquid crystal substance, it vibrates at the same angle as that of the final layer of the molecule vibrates. The light is allowed to enter into the device only if the second layer of the polarized glass matches with the final layer of the molecule.

III. How LCDs Work?

The principle behind the LCD’s is that when an electrical current is applied to the liquid crystal molecule, the molecule tends to untwist. This causes the angle of light which is passing through the molecule of the polarized glass and also cause a change in the angle of the top polarizing filter. As a result a little light is allowed to pass the polarized glass through a particular area of the LCD. Thus that particular area will become dark compared to other. The LCD works on the principle of blocking light. While constructing the LCD’s, a reflected mirror is arranged at the back. An electrode plane is made of indium-tin oxide which is kept on top and a polarized glass with a polarizing film is also added on the bottom of the device. The complete region of the LCD has to be enclosed by a common electrode and above it should be the liquid crystal matter.

Next comes to the second piece of glass with an electrode in the form of the rectangle on the bottom and, on top, another polarizing film. It must be considered that both the pieces are kept at right angles. When there is no current, the light passes through the front of the LCD it will be reflected by the mirror and bounced back. As the electrode is connected to a battery the current from it will cause the liquid crystals between the common-plane electrode and the electrode shaped like a rectangle to untwist. Thus the light is blocked from passing through. That particular rectangular area appears blank.

IV. Liquid Crystal Display of 16×2

The 16×2 liquid crystal display contains two horizontal lines and they are used for compressing the space of 16 display characters. In inbuilt, the LCD has two registers which are described below. The LCDs have a parallel interface, meaning that the microcontroller has to manipulate several interface pins at once to control the display. The interface consists of the following pins:

· A register select (RS) pin that controls where in the LCD's memory you're writing data to. You can select either the data register, which holds what goes on the screen, or an instruction register, which is where the LCD's controller looks for instructions on what to do next.

· A Read/Write (R/W) pin that selects reading mode or writing mode

· An Enable pin that enables writing to the registers

· 8 data pins (D0 -D7). The states of these pins (high or low) are the bits that you're writing to a register when you write, or the values you're reading when you read.

· There's also a display constrast pin (Vo), power supply pins (+5V and Gnd) and LED Backlight (Bklt+ and BKlt-) pins that you can use to power the LCD, control the display contrast, and turn on and off the LED backlight, respectively.

· The process of controlling the display involves putting the data that form the image of what you want to display into the data registers, then putting instructions in the instruction register. The LiquidCrystal Library simplifies this for you so you don't need to know the low-level instructions.The Hitachi-compatible LCDs can be controlled in two modes: 4-bit or 8-bit. The 4-bit mode requires seven I/O pins from the Arduino, while the 8-bit mode requires 11 pins. For displaying text on the screen, you can do most everything in 4-bit mode, so example shows how to control a 16x2 LCD in 4-bit mode.

· Pin1 (Vss):Ground pin of the LCD module.

· Pin2 (Vcc): Power to LCD module (+5V supply is given to this pin)

· Pin3 (VEE):Contrast adjustment pin. This is done by connecting the ends of a 10K potentimeter to +5V and ground and then connecting the slider pin to the VEE pin. The voltage at the VEE pin defines the contrast. The normal setting is between 0.4 and 0.9V.

· Pin4 (RS): Register select pin.The JHD162A has two registers namely command register and data register. Logic HIGH at RS pin selects data register and logic LOW at RS pin selects command register. If we make the RS pin HIGH and feed an input to the data lines (DB0 to DB7), this input will be treated as data to display on LCD screen. If we make the RS pin LOW and feed an input to the data lines, then this will be treated as a command ( a command to be written to LCD controller – like positioning cursor or clear screen or scroll).

· Pin5 (R/W): Read/Write modes. This pin is used for selecting between read and write modes. Logic HIGH at this pin activates read mode and logic LOW at this pin activates write mode.

· Pin6 (E): This pin is meant for enabling the LCD module. A HIGH to LOW signal at this pin will enable the module.

· Pin7 (DB0) to Pin14(DB7): Â These are data pins. The commands and data are fed to the LCD module though these pins.

· Pin15 (LED+): Anode of the back light LED. When operated on 5V, a 560 ohm resistor should be connected in series to this pin. In arduino based projects the back light LED can be powered from the 3.3V source on the arduino board.

· Pin16 (LED-): Cathode of the back light LED.

V. How to Calculate the Resistances for LCD:

· Resistance to adjust LCD Contrast:

On an LCD the potentiometer is used to adjust the bias level of the LCD - that is the contrast. You need to use it to set a voltage between Vcc and Vee, which you feed into Vo. That is, a voltage somewhere between +5V and -5V. Contrast adjustment; the best way is to use a variable resistor such as a potentiometer. The output of the potentiometer is connected to this pin. Rotate the potentiometer knob forward and backwards to adjust the LCD contrast. The contrast pin on the LCD requires a fairly small voltage for ideal display conditions.The lower the voltage the higher the contrast and vice versa.By using this formula we find the resistance value used across the led.Led resistor value can be calculated by Ohm’s law:

Vs = R x I
where:

V_sis the source voltage, measured in volts (V),
I is the current, measured in Amperes (Amps/A), and
R is the resistance, measured in Ohms (Ω).

 Example:

V_s= 5V
I = 5 mA (Minimum) & 50 mA (Maximum)
R = 1 K ohm & 100 ohm

From the calculation, we get 100 ohms to 1K ohm resistance for 5mA and 50 mA current.
but roughly use around 1 K ohm potentiometer. Only LCD’s Contrast will vary.

· Resistance to adjust LCD back light Intensity:

To improve visibility, particularly in dark locations, many LCDs (liquid crystal displays) include LEDs (light emitting diodes) behind the screen to provide a light source. This is called a back light.Some industry standard LCDs have 14-pin connectors and some have 16-pin connectors. The displays with 16-pin connectors usually use the top two pins for the back light. In this case, the Nanox LCD has a 14-pin connector with a separate LED back light.

Note: Do NOT hook power directly to the back light, or else it will instantly overheat and burn out. Instead, use a resistor to limit the current flow.

By using this formula we find the resistance value used across the led.Led resistor value can be calculated by Ohm’s law:

R=(V _s-V _led)/I _led

where:

V _sis the source voltage, measured in volts (V),

V _ledis the voltage drop across the LED, measured in volts (V),

I _ledis the current through the LED, measured in Amperes (Amps/A), and

R is the resistance, measured in Ohms (Ω).

· Example:

V_s= 5V

V_led= 3.7V

I_led= 20 mA

R = 65 ohm

From the calculation, get 65 ohms. but roughly we use around 70 ohm resistor. Only LED’s intensity will vary.

2. System modelling:

2.1 Circuit Diagram, Schematic diagram and PCB Layout:
Circuit Diagram

       Before wiring the LCD screen to your Arduino or Genuino board we suggest to solder a pin header strip to the 14 (or 16) pin count connector of the LCD screen, as you can see in the image above.
To wire your LCD screen to your board, connect the following pins
·  LCD RS pin to digital pin 13
·  LCD Enable pin to digital pin 12
·  LCD D4 pin to digital pin 5
· LCD D5 pin to digital pin 4
· LCD D6 pin to digital pin 3
·  LCD D7 pin to digital pin 2

Schematic Diagram

PCB Layout

2.2 Source Code programming:

2.1.1 LCD Interfacing with Arduino

Open the Arduino IDE and write the following program to blink an LED. I have written the Blink (File àExample à Basic à Liquid crystal à Display) example provided in the book Getting Started with Arduino. You may see the screenshot below. After writing the program you may save it with a file name of your choice (find File–>Save on menu bar of IDE)

To Download the code click here
Read About

I. How to select Board ?

II. How to compile program ?

III. How to get .hex file ?

Result:
1) Simulate design online click here to simulate

2) Published by, Electronics with shreyash

Download the code from here

2.2.2 20x4 LCD Interfacing with Arduino

The 20×4 LCD module pin out diagram is very much same as the 16×2 LCD module pin out diagram. It is same with the number of pins, order of pins and the purpose of pins. So the interfacing circuit diagram is also very same as the 16×2 LCD module with Arduino

Result:

1) Published by, Electronics with shreyash:

Download the code from here

2.2.3 Scrolling text display on LCD

A simple program for scrolling a text message on the LCD screen using Arduino is shown here. This is done using the “scroll()” method defined inside LiquidCrystal.h library. For example the method “lcd.scrollDisplayRight()” will scroll the display to right and the method”lcd.scrollDisplayLeft()” will scroll the display to left. A “for” loop is used for selecting the number of positions to scroll at a time. In the program shown below, it is chosen to be 2 because the text to be displayed is comparatively long. For shorter texts more number of positions must be scrolled at a time to get a smooth display.
Result:

1) Simulate design online, click here to simulate

2) Published by, Electronics with shreyash:

Download the code from here

2.2.4 Special character Display on LCD

Here is a simple example of how to create letter ‘b’ in CG-RAM.

The Array for generating ‘b’ is char b[7]={0x10,0x10,0x16,0x19,0x11,0x11,0x1E}; That is,

· Send address where you want to create character.

· Now create your character at this address. Send the ‘b’ character array values defined above one by one to the data register of LCD.

· To print the generated character at 0x40. Send command 0 to command register of LCD. The table below would explain this more clearly.

Result:
1) Simulate design online, click here to simulate

2) Published by, Electronics with shreyash:

Download the code from here

2. 2.4 Demultiplexing of LCD

We have seen parallel interface technique using Arduino library and we know that it requires 6 IO Lines, Now let’s see how we can reduce required IO’s using 74HC595. We know that we can reduce number IO required by using I2C based LCD interface circuit; It costs ten times more than 74HC595 Circuit

Result:

1) Published by, Electronics with shreyash:

Download the code from here

2.4 Design and play the game with Arduino

Design and play the game is simple with Arduino microcontroller which is another example of interfacing of LCD with Arduino.
Result:

1) Simulate design online, click here to simulate

2) Published by, Electronics with shreyash:

Download the code from here

See Also

· Liquid Crystal Library - reference for the Liquid Crystal library.

· lcd.begin()

· lcd.print()

· lcd.setCursor()

· Blink - Control of the block-style cursor.

· Cursor - Control of the underscore-style cursor.

· Display - Quickly blank the display without losing what's on it.

· TextDirection - Control which way text flows from the cursor.

· Scroll - Scroll text left and right.

· Serial display - Accepts serial input, displays it.

· SetCursor - Set the cursor position.

· Autoscroll - Shift text right and left.

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