lcd display c code brands
Before you get involved with LCD display programming, its critical you first choose the correct LCD display for your product. All LCD modules can be classified into one of two categories: those requiring a controller/driver chip and those that don"t.
Displays requiring a controller/driver chip to interface with your product require a programmer to write software code, sometimes referred to as firmware, to connect the LCD to the end product. Those that have a controller/driver are much easier and faster to program. Specifically, this article will address programming the character or alphanumeric displays with a parallel bus (a parallel bus LCD sends and receives 4 bits, 8 bits or 16 bits of data at a time).
The second category, those that don"t require a controller/driver chip, are called static or segment displays. This means that there is one connection on the LCD for each segment. Although this eliminates the controller chip, it requires a great deal of connections between the display and the customers product.
So what exactly is this all important piece of technology—the controller/driver (C/D)—that will make your life easier through quick and simple programming? It is a small microprocessor whose function is to convert the designers’ firmware/software into characters, numbers, and punctuation marks. The C/D makes it easy for the product designer to quickly program the character display. Inside each C/D is a character table, sometimes referred to as a character map or font table, which contains pre-loaded letters, numbers, and punctuation. The table allows the designer to call out the requested character by addressing the number of that character. In other words, the letter ‘T’ may be the number 27 and the n-dash (i.e. “-”) could be number 122. This eliminates the need to create each character from scratch and reduces the amount of time necessary to program the LCD module. In the font table shown below, the letter ‘P’ would be displayed when the designer calls the number sequence below.
D0=0, D1=0, D2=0, D3=0, D4 =0, D5=0, D6=1, D7=1. The letter Do, D1 and so on above means data bit 0, data bit 1 etc. Most character displays use eight data bits.
The character table contains 255 possible characters. This number of characters is sufficient for one language, but would be impossible to display every character in every language when limited to only 255 options. This challenge is solved by making use of a different C/D for each language. You can order a C/D for French, German and many other languages.
There are several manufactures of C/D’s including Seiko, Epson, Toshiba, and Sunplus. There are distinct advantages of having multiple makers in multiple places in the world. Specifically, you won’t have to worry about a delay in the supply chain that is the result from the constraint of the C/D being made by only one or two manufacturers. You don’t want anything to delay the launch of your product.
Character LCD displays contain 14 pins if no backlight is attached and 16 pins when an EL or LED backlight is included with the module. Below is a breakdown of each pin and the function of that pin. The function of these pins directly relates to your success at programming character LCD displays, so pay attention!
The Ground is necessary for the voltage and the contrast adjust to reference. Ground, also referred to as zero volts, is required on all electronic devices. Electrical ground is similar to the ground floor of a tall building. All the floors above the ground floor are positive and all the floors below the ground floor, the basement, are negative. The ground pin on the LCD is connected to the ground on the customer’s product
This is the Logic voltage necessary to drive the LCD. There are two common voltages for a character LCD, 3.3V (this is equal to two "aa" batteries in series) and 5V.
It is possible to order a character LCD with both a positive and negative voltage. This option is not very common and is seen in replacing older discontinued displays.
We do not recommend using the same Ground and VDD connections to supply both your LCD logic and your LED backlight. It is better to use a separate power for your backlight which is what pins 15 and 16 or the A and K tab on the side of the LCD are designed for.
This is the connection for the contrast adjust. This function is to modify the voltage between VDD and Ground and then to adjust the contrast. If you are not able to achieve the desired contrast, it may be necessary to add a resistor to the back of the printed circuit board. The addition of the resistor alleviates the low contrast issue.
Register Select has two positions: 1 (on or high) or 0 (off or low). When RS is low (0), the data is to be treated as an instruction such as ‘move the position of the cursor’ or ‘clear the screen’. When RS is high (1), the data being sent to the display is a letter, number or punctuation mark that is to be displayed on the screen.
The RW line is the "Read/Write" control line. When RW is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively querying (or reading) the LCD. Only one instruction ‘check LCD status’ is a read command. All others are write commands--so RW will almost always be set to low.
The data bits on a parallel LCD display can accept up to 8 bits of data at a time. It is possible to use just four of the eight data bits if your microcontroller lacks enough connections to drive all 8 bits; however, this is a slow transfer of information. The data bit lines are numbered DB and begin at number DB0, DB1 etc. up to DB7.
These two lines are called A for Anode and K for Cathode. Yes, it is strange to use the letter K for a word that starts with a C, but that is an entirely different subject!
The anode is the positive voltage for the backlight, while the K is the ground for the backlight. You have options when it comes to ordering your backlights; you can order an LCD display with either a 3.3V LED backlight or a 4.2V LED backlight.
One key component in LCD display programming is to make sure the controller driver you have designed will continue in production. Over time C/D suppliers will discontinue various models. So, the issue you solved with maintaining a steady supply chain does crop up again when models become obsolete. To mitigate the inconvenience, when the IC is discontinued, the LCD supplier will recommend a replacement or compatible controller. This is where the word ‘compatible’ does not mean ‘exact drop in equivalent’; however, we find that a compatible controller is an exact match 95% of the time. If you find yourself in that unlucky 5%, then you will either need to make a last-time buy of the controller that is being discontinued or change the software on your product to match the new controller.
The Hitachi type LCD displays are used in many designs. They work with an Arduino sketch on the IOT2020. If you"re building a C++ project, this driver class can help.
The full source code is attached. It contains an example that uses the SainSmart LCD shield - because I happen to have that one. It works with the typical one and two row LCD displays. Check that the pins you"re passing to the init() method match the ones of your design. If you are able to use your display on the Arduino UNO, use the same pin numbers here (I don"t use the RW pin, so no need to pass that one).
Methodsvoid init( uint32_t u_rs, uint32_t u_enable, uint32_t u_d0,uint32_t u_d1, uint32_t u_d2,uint32_t u_d3)void begin(uint32_t cols, uint32_t lines, uint32_t dotsize)void setCursor(uint32_t col, uint32_t row)void print(const std::string& input)
Example#include
The library that is used as the inspiration for this work has the following license (full version in the attached source). Please adhere to this:GNU Lesser General Public LicenseCopyright (C) 2006-2008 Hans-Christoph Steiner. All rights reserved.Copyright (c) 2010 Arduino LLC. All right reserved.
Edit: updated to use a separate source file for the driver .h and .cpp - the version 1.0.0 of the Siemens Eclipse plugin supported a single source file. This is fixed in 1.1.0
We come across Liquid Crystal Display (LCD) displays everywhere around us. Computers, calculators, television sets, mobile phones, and digital watches use some kind of display to display the time.
An LCD screen is an electronic display module that uses liquid crystal to produce a visible image. The 16×2 LCD display is a very basic module commonly used in DIYs and circuits. The 16×2 translates a display of 16 characters per line in 2 such lines. In this LCD, each character is displayed in a 5×7 pixel matrix.
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 backward to adjust the LCD contrast.
Sends data to data pins when a high to low pulse is given; Extra voltage push is required to execute the instruction and EN(enable) signal is used for this purpose. Usually, we set en=0, when we want to execute the instruction we make it high en=1 for some milliseconds. After this we again make it ground that is, en=0.
A 16X2 LCD has two registers, namely, command and data. The register select is used to switch from one register to other. RS=0 for the command register, whereas RS=1 for the data register.
Command Register: The command register stores the command instructions given to the LCD. A command is an instruction given to an LCD to do a predefined task. Examples like:
Data Register: The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. When we send data to LCD, it goes to the data register and is processed there. When RS=1, the data register is selected.
Generating custom characters on LCD is not very hard. It requires knowledge about the custom-generated random access memory (CG-RAM) of the LCD and the LCD chip controller. Most LCDs contain a Hitachi HD4478 controller.
CG-RAM is the main component in making custom characters. It stores the custom characters once declared in the code. CG-RAM size is 64 bytes providing the option of creating eight characters at a time. Each character is eight bytes in size.
CG-RAM address starts from 0x40 (Hexadecimal) or 64 in decimal. We can generate custom characters at these addresses. Once we generate our characters at these addresses, we can print them by just sending commands to the LCD. Character addresses and printing commands are below.
LCD modules are very important in many Arduino-based embedded system designs to improve the user interface of the system. Interfacing with Arduino gives the programmer more freedom to customize the code easily. Any cost-effective Arduino board, a 16X2 character LCD display, jumper wires, and a breadboard are sufficient enough to build the circuit. The interfacing of Arduino to LCD display is below.
The combination of an LCD and Arduino yields several projects, the most simple one being LCD to display the LED brightness. All we need for this circuit is an LCD, Arduino, breadboard, a resistor, potentiometer, LED, and some jumper cables. The circuit connections are below.
If you’ve ever attempted to connect an LCD display to an Arduino, you’ve probably noticed that it uses a lot of Arduino pins. Even in 4-bit mode, the Arduino requires seven connections – half of the Arduino’s available digital I/O pins.
The solution is to use an I2C LCD display. It only uses two I/O pins that are not even part of the digital I/O pin set and can be shared with other I2C devices.
As the name suggests, these LCDs are ideal for displaying only characters. A 16×2 character LCD, for example, can display 32 ASCII characters across two rows.
If you look closely, you can see tiny rectangles for each character on the screen as well as the pixels that make up a character. Each of these rectangles is a grid of 5×8 pixels.
At the heart of the adapter is an 8-bit I/O expander chip – PCF8574. This chip converts the I2C data from an Arduino into the parallel data required for an LCD display.
There is a jumper on the board that provides power to the backlight. To control the intensity of the backlight, you can remove the jumper and apply external voltage to the header pin labeled ‘LED’.
If you have multiple devices on the same I2C bus, you may need to set a different I2C address for the LCD adapter to avoid conflicting with another I2C device.
For this purpose, the adapter comes with three solder jumpers/pads (A0, A1, and A2). The address is set when a jumper is shorted with a blob of solder.
An important point to note here is that several companies, including Texas Instruments and NXP Semiconductors, manufacture the same PCF8574 chip. And the I2C address of your LCD depends on the chip manufacturer.
According to the Texas Instruments’ datasheet, the three address selection bits (A0, A1, and A2) are located at the end of the 7-bit I2C address register.
According to the NXP Semiconductors’ datasheet, the three address selection bits (A0, A1, and A2) are located at the end of the 7-bit I2C address register. However, the remaining bits in the address register are different.
So the I2C address of your LCD is most likely 0x27 or 0x3F. If you’re not sure what your LCD’s I2C address is, there’s an easy way to figure it out. You’ll learn about that later in this tutorial.
Now we are left with the pins that are used for I2C communication. Note that each Arduino board has different I2C pins that must be connected correctly. On Arduino boards with the R3 layout, the SDA (data line) and SCL (clock line) are on the pin headers close to the AREF pin. They are also referred to as A5 (SCL) and A4 (SDA).
After wiring the LCD, you will need to adjust the contrast of the LCD. On the I2C module, there is a potentiometer that can be rotated with a small screwdriver.
Now, turn on the Arduino. You will see the backlight light up. As you turn the potentiometer knob, the first row of rectangles will appear. If you have made it this far, Congratulations! Your LCD is functioning properly.
Before you can proceed, you must install the LiquidCrystal_I2C library. This library allows you to control I2C displays using functions that are very similar to the LiquidCrystal library.
To install the library, navigate to Sketch > Include Library > Manage Libraries… Wait for the Library Manager to download the library index and update the list of installed libraries.
Filter your search by entering ‘liquidcrystal‘. Look for the LiquidCrystal I2C library by Frank de Brabander. Click on that entry and then choose Install.
As previously stated, the I2C address of your LCD depends on the manufacturer. If your LCD has a PCF8574 chip from Texas Instruments, its I2C address is 0x27; if it has a PCF8574 chip from NXP Semiconductors, its I2C address is 0x3F.
If you’re not sure what your LCD’s I2C address is, you can run a simple I2C scanner sketch that scans your I2C bus and returns the address of each I2C device it finds.
However, before you upload the sketch, you must make a minor change to make it work for you. You must pass the I2C address of your LCD as well as the display dimensions to the LiquidCrystal_I2C constructor. If you’re using a 16×2 character LCD, pass 16 and 2; if you’re using a 20×4 character LCD, pass 20 and 4.
The next step is to create an object of LiquidCrystal_I2C class. The LiquidCrystal_I2C constructor accepts three inputs: I2C address, number of columns, and number of rows of the display.
In the setup, three functions are called. The first function is init(). It initializes the interface to the LCD. The second function is clear(). This function clears the LCD screen and positions the cursor in the upper-left corner. The third function, backlight(), turns on the LCD backlight.
The function setCursor(2, 0) is then called to move the cursor to the third column of the first row. The cursor position specifies where you want the new text to appear on the LCD. It is assumed that the upper left corner is col=0 and row=0.
There are many useful functions you can use with LiquidCrystal_I2C Object. Some of them are listed below:lcd.home() function positions the cursor in the upper-left of the LCD without clearing the display.
lcd.scrollDisplayRight() function scrolls the contents of the display one space to the right. If you want the text to scroll continuously, you have to use this function inside a for loop.
lcd.scrollDisplayLeft() function scrolls the contents of the display one space to the left. Similar to the above function, use this inside a for loop for continuous scrolling.
lcd.display() function turns on the LCD display, after it’s been turned off with noDisplay(). This will restore the text (and cursor) that was on the display.
If you find the default font uninteresting, you can create your own custom characters (glyphs) and symbols. They come in handy when you need to display a character that isn’t in the standard ASCII character set.
As previously discussed in this tutorial, a character is made up of a 5×8 pixel matrix; therefore, you must define your custom character within this matrix. You can define a character by using the createChar() function.
To use createChar(), you must first create an 8-byte array. Each byte in the array corresponds to a row in a 5×8 matrix. In a byte, the digits 0 and 1 indicate which pixels in a row should be OFF and which should be ON.
CGROM is non-volatile memory that retains data even when the power is removed, whereas CGRAM is volatile memory that loses data when the power is removed.
The CGROM stores the font that appears on a character LCD. When you instruct a character LCD to display the letter ‘A’, it needs to know which pixels to turn on so that we see an ‘A’. This data is stored in the CGROM.
CGRAM is an additional memory for storing user-defined characters. This RAM is limited to 64 bytes. Therefore, for a 5×8 pixel LCD, only 8 user-defined characters can be stored in CGRAM, whereas for a 5×10 pixel LCD, only 4 can be stored.
Creating custom characters has never been easier! We’ve developed a small application called Custom Character Generator. Can you see the blue grid below? You can click on any pixel to set or clear that pixel. And as you click, the code for the character is generated next to the grid. This code can be used directly in your Arduino sketch.
There’s no limit to what you can create. The only limitation is that the LiquidCrystal_I2C library only supports eight custom characters. But don’t be sad, look at the bright side; at least we have eight characters.
After including the library and creating the LCD object, custom character arrays are defined. The array consists of 8 bytes, with each byte representing a row in a 5×8 matrix.
This sketch contains eight custom-characters. Take, for example, the Heart[8] array. You can see that the bits (0s and 1s) are forming the shape of a heart. 0 turns the pixel off, and 1 turns it on.
In the setup, we use the createChar() function to create a custom character. This function accepts two parameters: a number between 0 and 7 to reserve one of the eight supported custom characters, and the name of the array.
LCD character displays are useful for displaying information without the need for an external monitor. Common LCD character displays can be connected directly to the GPIO pins, but such an approach requires the use of up to 10 GPIO pins. For scenarios that require connecting to a combination of devices, devoting so much of the GPIO header to a character display is often impractical.
Many manufacturers sell 20x4 LCD character displays with an integrated GPIO expander. The character display connects directly to the GPIO expander, which then connects to the Raspberry Pi via the Inter-Integrated Circuit (I2C) serial protocol.
There are many manufacturers of LCD character displays. Most designs are identical, and the manufacturer shouldn"t make any difference to the functionality. For reference, this tutorial was developed with the SunFounder LCD2004.
A using declaration creates an instance of I2cDevice by calling I2cDevice.Create and passing in a new I2cConnectionSettings with the busId and deviceAddress parameters. This I2cDevice represents the I2C bus. The using declaration ensures the object is disposed and hardware resources are released properly.
The device address for the GPIO expander depends on the chip used by the manufacturer. GPIO expanders equipped with a PCF8574 use the address 0x27, while those using PCF8574A chips use 0x3F. Consult your LCD"s documentation.
Another using declaration creates an instance of Lcd2004 to represent the display. Several parameters are passed to the constructor describing the settings to use to communicate with the GPIO expander. The GPIO expander is passed as the controller parameter.
Deploy the app to the Raspberry Pi as a self-contained app. For instructions, see Deploy .NET apps to Raspberry Pi. Make sure to give the executable execute permission using chmod +x.
I am working with a Winstar Display LCD ( WH2004A-YYK-CP ) and STM32 processor and codes are written in C. I need to run it with 4-bit mode. I run it and wrote what I wanted.
As you know, 4-bit mode send 8-bit data as 2 times 4bit. The problem is, when I reset between 2 nibbles, it prints strange characters, and no matter how much I reset it, it is not working properly. The only solution I came up is resetting it several times.
To figure out what is going on, I added 2 second delay between 2 nibbles (4-bit each), and print a long sentence. therefore whenever I reset it, processor waiting to send second nibble.
I am resetting it, it prints something strange, after second reset it prints nothing, and after third one it prints again correctly. and 4th reset it again prints something strange, 5th one prints nothing and 6th one again prints correctly ... and goes on like this.
How can I be sure that "when I reset STM32 processor, LCD is not waiting second nibble of some data whose first nibble is sent in the previous session." by using C codes?
As a 2inch IPS display module with a resolution of 240 * 320, it uses an SPI interface for communication. The LCD has an internal controller with basic functions, which can be used to draw points, lines, circles, and rectangles, and display English, Chinese as well as pictures.
The 2inch LCD uses the PH2.0 8PIN interface, which can be connected to the Raspberry Pi according to the above table: (Please connect according to the pin definition table. The color of the wiring in the picture is for reference only, and the actual color shall prevail.)
The example we provide is based on STM32F103RBT6, and the connection method provided is also the corresponding pin of STM32F103RBT6. If you need to transplant the program, please connect according to the actual pin.
The LCD supports 12-bit, 16-bit, and 18-bit input color formats per pixel, namely RGB444, RGB565, and RGB666 three color formats, this demo uses RGB565 color format, which is also a commonly used RGB format.
For most LCD controllers, the communication mode of the controller can be configured, usually with an 8080 parallel interface, three-wire SPI, four-wire SPI, and other communication methods. This LCD uses a four-wire SPI communication interface, which can greatly save the GPIO port, and the communication speed will be faster.
Note: Different from the traditional SPI protocol, the data line from the slave to the master is hidden since the device only has display requirement.
CPOL determines the level of the serial synchronous clock at idle state. When CPOL = 0, the level is Low. However, CPOL has little effect to the transmission.
CPHA determines whether data is collected at the first clock edge or at the second clock edge of serial synchronous clock; when CPHL = 0, data is collected at the first clock edge.
PS: If you are using the system of the Bullseye branch, you need to change "apt-get" to "apt", the system of the Bullseye branch only supports Python3.
Framebuffer uses a video output device to drive a video display device from a memory buffer containing complete frame data. Simply put, a memory area is used to store the display content, and the display content can be changed by changing the data in the memory.
There is an open source project on github: fbcp-ili9341. Compared with other fbcp projects, this project uses partial refresh and DMA to achieve a speed of up to 60fps
Note: The script will replace the corresponding /boot/config.txt and /etc/rc.local and restart, if the user needs, please back up the relevant files in advance.
We have carried out the low-level encapsulation, if you need to know the internal implementation can go to the corresponding directory to check, for the reason that the hardware platform and the internal implementation are different
2.We use Dev libraries by default. If you need to change to BCM2835 or WiringPi libraries ,please open RaspberryPi\c\Makefile and modify lines 13-15 as follows:
If you need to draw pictures, or display Chinese and English characters, we provide some basic functions here about some graphics processing in the directory RaspberryPi\c\lib\GUI\GUI_Paint.c(.h).
Select image buffer: The purpose of the selection is that you can create multiple image attributes, there can be multiple images buffer, you can select each image you create.
Mirror: indicates the image mirroring mode. MIRROR_NONE, MIRROR_HORIZONTAL, MIRROR_VERTICAL, MIRROR_ORIGIN correspond to no mirror, horizontal mirror, vertical mirror, and image center mirror respectively.
Set points of the display position and color in the buffer: here is the core GUI function, processing points display position and color in the buffer.
The fill color of a certain window in the image buffer: the image buffer part of the window filled with a certain color, usually used to fresh the screen into blank, often used for time display, fresh the last second of the screen.
Draw rectangle: In the image buffer, draw a rectangle from (Xstart, Ystart) to (Xend, Yend), you can choose the color, the width of the line, whether to fill the inside of the rectangle.
Draw circle: In the image buffer, draw a circle of Radius with (X_Center Y_Center) as the center. You can choose the color, the width of the line, and whether to fill the inside of the circle.
Write Ascii character: In the image buffer, use (Xstart Ystart) as the left vertex, write an Ascii character, you can select Ascii visual character library, font foreground color, font background color.
Write English string: In the image buffer, use (Xstart Ystart) as the left vertex, write a string of English characters, you can choose Ascii visual character library, font foreground color, font background color.
Write Chinese string: in the image buffer, use (Xstart Ystart) as the left vertex, write a string of Chinese characters, you can choose character font, font foreground color, font background color of the GB2312 encoding
Write numbers: In the image buffer,use (Xstart Ystart) as the left vertex, write a string of numbers, you can choose Ascii visual character library, font foreground color, font background color.
Display time: in the image buffer,use (Xstart Ystart) as the left vertex, display time,you can choose Ascii visual character font, font foreground color, font background color.;
2. The module_init() function is automatically called in the INIT () initializer on the LCD, but the module_exit() function needs to be called by itself
Python has an image library PIL official library link, it do not need to write code from the logical layer like C, can directly call to the image library for image processing. The following will take 1.54inch LCD as an example, we provide a brief description for the demo.
The first parameter defines the color depth of the image, which is defined as "1" to indicate the bitmap of one-bit depth. The second parameter is a tuple that defines the width and height of the image. The third parameter defines the default color of the buffer, which is defined as "WHITE".
The first argument is a tuple of four elements. (20,10) is the coordinate value in the upper left corner of the rectangle, and (70,60) is the coordinate value in the lower right corner of the rectangle. Fill =" WHITE" means BLACK inside, and outline="BLACK" means the color of the outline is black.
Draw an inscribed circle in the square, the first parameter is a tuple of 4 elements, with (150, 15) as the upper left corner vertex of the square, (190, 55) as the lower right corner vertex of the square, specifying the level median line of the rectangular frame is the angle of 0 degrees, the second parameter indicates the starting angle, the third parameter indicates the ending angle, and fill = 0 indicates that the the color of the line is white.
The first parameter is the coordination of the enclosing rectangle. The second and third parameters are the beginning and end degrees of the circle. The fourth parameter is the fill color of the circle.
Note: Each character library contains different characters; If some characters cannot be displayed, it is recommended that you can refer to the encoding set ro used.
The first parameter is a tuple of 2 elements, with (40, 50) as the left vertex, the font is Font2, and the fill is the font color. You can directly make fill = "WHITE", because the regular color value is already defined Well, of course, you can also use fill = (128,255,128), the parentheses correspond to the values of the three RGB colors so that you can precisely control the color you want. The second sentence shows Micro Snow Electronics, using Font3, the font color is white.
If you plan on using an LCD with your Raspberry Pi, there’s a good chance you’ll need to program it in Python at some point. Python is probably the most popular programming language for coding on the Raspberry Pi, and many of the projects and examples you’ll find are written in Python.
In this tutorial, I’ll show you how to connect your LCD and program it in Python, using the RPLCD library. I’ll start with showing you how to connect it in either 8 bit mode or 4 bit mode. Then I’ll explain how to install the library, and provide examples for printing and positioning text, clearing the screen, and controlling the cursor. I’ll also give you examples for scrolling text, creating custom characters, printing data from a sensor, and displaying the date, time, and IP address of your Pi.
BONUS: I made a quick start guide for this tutorial that you can download and go back to later if you can’t set this up right now. It covers all of the steps, diagrams, and code you need to get started.
You can also connect the LCD via I2C, which uses only two wires, but it requires some extra hardware. Check out our article, How to Setup an I2C LCD on the Raspberry Pi to see how.
There are two ways to connect the LCD to your Raspberry Pi – in 4 bit mode or 8 bit mode. 4 bit mode uses 6 GPIO pins, while 8 bit mode uses 10. Since it uses up less pins, 4 bit mode is the most common method, but I’ll explain how to set up and program the LCD both ways.
Each character and command is sent to the LCD as a byte (8 bits) of data. In 8 bit mode, the byte is sent all at once through 8 data wires, one bit per wire. In 4 bit mode, the byte is split into two sets of 4 bits – the upper bits and lower bits, which are sent one after the other over 4 data wires.
Theoretically, 8 bit mode transfers data about twice as fast as 4 bit mode, since the entire byte is sent all at once. However, the LCD driver takes a relatively long time to process the data, so no matter which mode is being used, we don’t really notice a difference in data transfer speed between 8 bit and 4 bit modes.
If this is your first time writing and running a Python program, you might want to read How to Write and Run a Python Program on the Raspberry Pi, which will explain everything you need to know to run the examples below.
The RPLCD library can be installed from the Python Package Index, or PIP. It might already be installed on your Pi, but if not, enter this at the command prompt to install it:
The example programs below use the Raspberry Pi’s physical pin numbers, not the BCM or GPIO numbers. I’m assuming you have your LCD connected the way it is in the diagrams above, but I’ll show you how to change the pin connections if you need to.
Let’s start with a simple program that will display “Hello world!” on the LCD. If you have a different sized LCD than the 16×2 I’m using (like a 20×4), change the number of columns and rows in line 2 of the code. cols= sets the number of columns, and rows= sets the number of rows. You can also change the pins used for the LCD’s RS, E, and data pins. The data pins are set as pins_data=[D0, D1, D2, D3, D4, D5, D6, D7].
The text can be positioned anywhere on the screen using lcd.cursor_pos = (ROW, COLUMN). The rows are numbered starting from zero, so the top row is row 0, and the bottom row is row 1. Similarly, the columns are numbered starting at zero, so for a 16×2 LCD the columns are numbered 0 to 15. For example, the code below places “Hello world!” starting at the bottom row, fourth column:
The RPLCD library provides several functions for controlling the cursor. You can have a block cursor, an underline cursor, or a blinking cursor. Use the following functions to set the cursor:
Text will automatically wrap to the next line if the length of the text is greater than the column length of your LCD. You can also control where the text string breaks to the next line by inserting \n\r where you want the break to occur. The code below will print “Hello” to the top row, and “world!” to the bottom row.
This program will print the IP address of your ethernet connection to the LCD. To print the IP of your WiFi connection, just change eth0 in line 19 to wlan0:
Each character on the LCD is an array of 5×8 of pixels. You can create any pattern or character you can think of, and display it on the screen as a custom character. Check out this website for an interactive tool that creates the bit array used to define custom characters.
First we define the character in lines 4 to 12 of the code below. Then we use the function lcd.create_char(0-7, NAME) to store the character in the LCD’s CGRAM memory. Up to 8 (0-7) characters can be stored at a time. To print the custom character, we use lcd.write_string(unichr(0)), where the number in unichr() is the memory location (0-7) defined in lcd.create_char().
To demonstrate how to print data from a sensor, here’s a program that displays the temperature from a DS18B20 Digital Temperature Sensor. There is some set up to do before you can get this to work on the Raspberry Pi, so check out our tutorial on the DS18B20 to see how.
In general, you take the input variable from your sensor and convert it to an integer to perform any calculations. Then convert the result to a string, and output the string to the display using lcd.write_string(sensor_data()):
Well, that about covers most of what you’ll need to get started programming your LCD with Python. Try combining the programs to get some interesting effects. You can display data from multiple sensors by printing and clearing the screen or positioning the text. You can also make fun animations by scrolling custom characters.
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Ms.Josey 
Ms.Josey