raspbian lcd displays random characters brands
Many of these LCD controllers differ slightly from the HD44780 controller in things like the initialization sequence, minimum delay between commands and maybe other ways I don"t know of.
try putting a 1n4148 diode between the 5V supply and the 5V of the LCD, so the LCD will get around 4.5V, that is enough for the LCD, and lowers its logical input levels enough so that it sees 3V3 logic highs as "1" reliably. The garbled letters, and blocks are due to the LCD sometimes seeing a "1" as a zero and that corrupts all communication between the PI and the LCD.
Its a well know problem when trying to drive an LCD with 3V3 levels, it actually needs minimally 3.5V when its powered with 5V (70 % of VCC = 0.7 x 5.0 = 3.5).
In the photos above the Pi is a Model B Rev 2 so should work fine with my tutorial. Random characters is usually a sign it has not been initialized correctly. Again this could be caused by intermittent connections.
I was having the same problem as the OP on my current build with an I2C back-packed LCD getting corrupted. I"d tried all kinds of things to fix the problems - changing the delays, trying different libraries, and pulling out hair with no joy in fixing it.
For anyone else with this problem, you may have what I have if you"re doing event-driven code e.g. from from a switch or rotary encoder. I was getting events triggered while the python code was trying to communicate with the LCD screen - which themselves tried to write to the LCD.
I also had the same problem with scrambled characters on my display. I found that there was a short between the data lines on the expander board where it is soldered to the display board. Once I cleaned up the messy solder, the display worked perfectly.
My code seems to work for outputting to the console, however when I try to output to the LCD, it gives some weird characters and stops. Not sure what to do as i"m not a python wiz (you"d think id be more like php, but nah lol).
I am trying to use a 4x20 LCD display with RPLCD module. Its working. But if I run the program ten times every four or five times LCD shows these three garbage values(See below images). Here is my code:
If your keyboard is outputting the wrong characters for that key then the Pi is probably using an incorrect keyboard layout. The most common example is a " " " being printer when you press the " @ " key. This can be fixed easily in the configuration tool, type "sudo raspi-config" into the terminal. Then select "Localisation Options" and then "Change Keyboard Layout", this will match the keyboard layout to the type of keyboard you have connected to the Raspberry Pi.
After a few hours, even using the lcd module I recommended above, the random jibberish appeared again. By using RUI’s example from his “Home Automation Using 8266, Project 6, Unit 4 (which uses an ESP8266 instead of ESP32, I no longer get jibberish.
I have been struggling for days with the same issue. what did help me getting rid of the “random gibberish” is to put 10k pullup resistors to VCC on both the data and clock lines
Also create a sketch that uses the 10K pullups using the same libraries, LCD and sensor with MQTT, in other words just reading the temperature and displaying it to the LCD and then it works.
In place of lcd.clear(), use lcd.setCursor(0, row) where row is the row you want to clear, than fill it with spaces ” ” like this: lcd.print(std::string(” “, lcdColumns).c_str()). After go back to the init of the row with setCursor and write what you want.
For slow down and not have bad characters use this before print in lcd: Wire.setClock(10000), i tried only in setup() but it not worked, maybe because of rtos task in the example. you need to #include
When I start my code, it displays as expected the initial screen on the LCD (as defined in setup() function) and then the temperature. But suddenly the LCD displays random characters, see attached, and somehow never stop displaying random characters until i restart the board.
Warning: Arduino and other systems with bootloaders may send "garbage" characters to the display while the system is starting up or being reprogrammed. This may cause the display to be bricked. To avoid this, you can use a software serial library to create a separate serial port from the USB port, as in the following examples. For more information about the library, head over to the reference:
For simplicity, we will be using an Arduino microcontroller. In this example, we connected a serial enabled LCD to the RedBoard programmed with Arduino (basically an Arduino Uno with an ATmega328P).
When you power up the board, you"ll briefly see a SparkFun splash screen, and then the display will go blank. To send text to the board, wait 1/2 second (500ms) after power up for the splash screen to clear, then send text to the display through your serial port. The display understands all of the standard ASCII characters (upper and lowercase text, numbers, and punctuation), plus a number of graphic symbols and Japanese characters. See the HD44780 datasheet for the full list of supported characters.
A common LCD technique is to repeatedly display changing numbers such as RPM or temperature in the same place on the display. You can easily do this by moving the cursor before sending your data.
To move the cursor, send the special character (0xFE), followed by the cursor position you"d like to set. Each cursor position is represented by a number, see the table below to determine the number in decimal to send for a serial enabled LCD set to 16x2:
Computers seem good at random number generation. But in truth their random numbers are merely pseudorandom because computer programs are inherently deterministic. Here, Dev presents a random number generator that uses machine vision to acquire true randomness from a physical source.
In the time before computers (BC), our ancestors used simple methods, such as throwing dice, to generate random numbers. Although our computers seem to be capable of spewing random numbers at a much higher rate, these numbers are not random, they’re pseudorandom. Computer programs are deterministic algorithms that are completely predictable at some base level. In this article, I share my design of a random number generator based on the Raspberry Pi that uses machine vision to harvest true randomness from a physical source.
An important part of my childhood education was frequent trips to the public library. Our city with a population of 100,000 had a huge public library that was well stocked with books and periodicals. I enjoyed randomly browsing the stacks—the yesteryear equivalent of evoking the random page feature on Wikipedia [1]. In my adventures among the stacks, I chanced upon an article that described an early attempt at using random numbers to generate poetry using a computer. This work was done at Bell Labs, where random numbers were likewise used to create art and computer music.
Reading that article was one of several things that sparked my interest in random numbers and random number generation that continued throughout my career. In the days of impact printing, I used random numbers to program the daisy wheel printer in my office in a simulation that made it sound as if I was hard at work typing when my office door was closed. In that case, the randomness was 1/f noise—a type of noise that’s less random than white noise.
Human culture has embraced randomness in such activities as reading tea leaves and flipping Tarot cards for predicting the future. Throwing dice in gaming has been done for millennia, and randomness is built into our modern slot machines. There are non-gaming uses of randomness in computer simulation, such as the Monte Carlo method used in physics, statistical sampling and statistical analysis of experiments.
Most computer applications will perform adequately using simple random number generators, but due care must be taken in the generation of cryptographic quality random numbers—the ones that are used to encode secret communications against technologically advanced adversaries. Just as an individual would be unwise to use “1234” as a PIN number, cryptographers want to “seed” their random number generators with unique starting values to produce better randomness.
Programming languages have always had random number functions, and these have improved over the decades. The earliest of these used a simple algorithm called a linear congruential generator (LCG). The GNU C compiler uses an improved version of this generator, but LCGs should not be used when good quality random numbers are needed. Many of today’s languages, including Python and PHP, use a much more complicated algorithm called the Mersenne Twister, which, as its name implies, involves the Mersenne primes [2].
Aside from its being a generalized feedback shift register, it’s somewhat hard to describe. It’s used as the random number generator not only in Python and PHP, but also the popular Mathworks MATLAB environment, the R statistical package and some other programming languages. It has a 32-bit implementation, called MT19937, based on the 24th Mersenne prime, that has a period 219937 – 1. There is also a 64-bit version called MT19937-64 [3].
As computer pioneer, John von Neumann, so famously stated in 1951: “Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.” He realized that computers just follow some algorithm to generate their random numbers, so these apparently random numbers are completely predictable if the algorithm and its initial state is known. That didn’t stop him from using such random numbers for mathematical modeling of complex systems, since they’re good enough for such things. However, their potential predictability makes them not well suited for cryptography. That’s why sources of true randomness are important.
Nature has given us many sources of true randomness. In 1926, John B. Johnson of Bell Labs discovered that any resistor at temperatures above absolute zero has a random voltage noise across its terminals. Harry Nyquist, a colleague of his at Bell Labs, was able to explain this phenomenon, and we now call it Johnson-Nyquist noise. This noise is very small. A 1kΩ resistor at room temperature—measured over a 10kHz bandwidth—has an RMS (root mean square) noise voltage of just 400nV, but it can be amplified and used to generate random numbers.
A Zener diode noise source. The amplification needs to be large, and this leads to the addition of amplifier noise to the signal. While truly random noise (“white noise”) is independent of frequency, amplifier noise has a frequency dependence. Amplifier noise is “1/f noise” also called “flicker noise.”
Heisenberg’s uncertainty principle is a well known feature of quantum mechanics, and uncertainty is a source of randomness. This sentiment was echoed by Einstein, who wrote that quantum mechanics was like “God playing dice with the world.” Radioactive decay in the tick-tick of a Geiger counter can be a source of random numbers, because the time interval between ticks is random. Since Geiger counters should click very slowly, scientists at the National Institute of Standards and Technology (NIST) developed a quantum voltage noise source (QVNS) in 1999. Their QVNS uses a superconducting junction based on a quantum mechanical effect known as the Josephson effect.
It’s unlikely that you will stock QVNS chips in your electronics parts bin, given that they only work at cryogenic temperatures. However, NIST has an online Randomness Beacon (https://beacon.nist.gov/home) that produces a 512-bit random number every minute—together with a timestamp of its creation—and a hash with the previous value. The Beacon website does have one caveat: The random numbers should not be used as cryptographic keys.
One novel physical random number generator, created in the late 1990s by Silicon Graphics, is Lavarand. Lavarand generated random numbers from images of active lava lamps. The images are random, since the behavior of the bubbles of simulated lava is not predictable (Figure 2). The method of creating random numbers from images is described in US Patent No. 5,732,138, “Method for seeding a pseudo-random number generator with a cryptographic hash of a digitization of a chaotic system [4].” There was once a Lavarand website that served-up random numbers, but Silicon Graphics is now defunct, and so is the web site.
The lava lamp idea has been picked up by the website-security company, Cloudflare, which has a Wall of Entropy at its San Francisco offices [5]. The Wall of Entropy has multiple rows of lava lamps that are imaged to produce random numbers. These numbers are combined with random numbers from other sources of randomness to produce random numbers presumed to be cryptographically secure. Cloudflare has joined with other international randomness creators to form a “League of Entropy” to distribute random numbers on the Internet [6].
A wall of lava lamps would be a decorative addition to my home office, but there are less expensive ways to produce physical randomness. I searched craft stores and supermarket shelves looking for some suitable candidates. Shown in Figure 3 are 50:50 mixtures of easily obtained black and white components. High contrast between black and white is preferred.
Household sources of image randomness. (a) Black and clear plastic craft beads. (b) Black dyed and white pearled couscous pasta. (c) Black and white microbeads used as fingernail decoration. (c) Oriental black rice and white rice.
Figure 3c shows a much better option. These are 0.6mm microbeads used in fingernail art, not stocked in any of my local stores, but available online. The material that’s easiest to find is rice. I learned from a restaurant visit several years ago that there’s such a thing as black rice, and this rice is found in any oriental grocery store. Mixing the black rice with a white rice produces an excellent random image noise source, since the rice grains have a matte finish that doesn’t reflect light. A quick shake of any of these sources produces a new random image.
Machine vision is simplified by the presence of USB ports on the Raspberry Pi and the availability of inexpensive USB interfaced video cameras. These cameras, typically used for video conferencing, produce high-definition color video images and they operate over a large range of light levels. Our basic machine vision physical random number generator is built around the Raspberry Pi, one of these cameras (a YoLuke HD Webcam), an LED light source and a liquid crystal character display connected to the I2C capable GPIO pins of the Raspberry Pi. Linux—in the form of the popular Raspberry Pi OS operating system (previously called Raspbian)—has utilities that simplify stitching these hardware components together with software [7].
Our first problem is trying to stuff all these components into a small, elegant enclosure. The camera needs a reasonably large offset from the plane of the random elements to focus and image the entire area. To accomplish this, I used a folded optical system in which a mirror bends the image from the top of the device through 90-degrees to a side-looking camera (Figure 4). The random elements are contained in a 2″ square plastic cube that’s placed at the top of the enclosure. There’s a leaf switch at the top that detects when the cube is removed, presumably shaken and then replaced.
Mechanical layout of the machine vision physical random number generator. Fortunately, the video camera could easily focus down to the necessary 4″ optical path length. The micro USB power connector for the Raspberry Pi was attached to a short adapter cable with a standard USB receptacle for connection at the rear of the enclosure for the power source.
While the Raspberry Pi gives an easy way to acquire a digital image, we still need to get a signal from the leaf switch and present the random numbers to the outside world. In this random number generator, communication is accomplished in two ways. First, there’s an interface board the converts the 3.3V GPIO signals of the Raspberry Pi to the 5V signals needed by an LCD display on the front panel. Inexpensive character displays with an I2C digital interface are available from many sources, and a backlit display was used in this project. Since the Raspberry Pi has a built-in Wi-Fi interface, the random numbers are also served as a webpage on your home network. Figure 5 shows the circuit diagram for the interface board, and Figure 6 is a component side view of the circuit board showing the connections.
Circuit diagram for the interface board. This board provides voltage level-shifting from the 3.3V logic of the Raspberry Pi to the 5V logic needed for the LCD display. It also powers the illumination LEDs, the LCD backlight, interfaces to the leaf switch that indicates when the cube of random material has been removed and replaced and a push-button power-off switch explained in the text. Connect “A” to “A” and “B” to “B”.
in which my_program.c is the source code, and the -o option specifies the name of the executable, in this case, myprogram. The -Wall option presents a list of program warnings and errors that need attention. I used C language for the main program because it facilitates the image processing and conversion of the physical randomness of the image. Python is a better language for controlling the I2C display interface and the other GPIO pins. For that reason, the main program calls a Python helper program to accomplish such tasks. The main program likewise produces a data file that’s used to present the random numbers on a web page.
It’s straightforward getting the image data into a numerical array for extraction of the random numbers, but creation of quality randomness takes a little effort. Because the image data is represented by pixel values in the range of 0-255, we can set a mid-range value of 127 and generate a “1” bit for values at that point and larger, and a “0” bit for numbers less than that.
The resultant bitstream is somewhat random, but it’s biased in several ways. For example, the white and black elements might have a slightly different electrostatic attraction to each other, and they might clump. Also, as in the case of using the black and white rice, the individual elements extend over many pixels, so there’s some correlation. For these reasons, we select pixels randomly using the random function of our programming language and go through a “whitening” step. Using software randomness in this case is allowed, since our physical system is unpredictable.
Whitening is a means of extracting randomness from a slightly biased random source, such as loaded dice, and a simple whitening method was invented by computer pioneer, John von Neumann. This von Neumann Whitening operates on two successive bits at a time, and maps them to a random stream as follows: (0,1) gives a 0, (1,0) gives a 1, and (0,0) or (1,1) gives a result that’s ignored. The random number in our machine vision system is created by randomly fetching pixels from the image, applying the threshold function to give a 0 or 1, whitening this bit stream and extracting a 64-bit hexadecimal number.
A 2 line by 16-character LCD display with an I2C serial interface is used to display the random numbers. The display chosen uses a Hitachi HD44780 compatible controller, as does nearly every such display. To make such displays I2C displays, they have an additional Texas Instruments (TI) PCF8574 chip that acts as a serial to parallel converter. Connection to the rest of the circuitry is through just four pins for +5Vt power, ground and the I2C SDA and SCL data lines (Figure 7). The display I used has a blue backlight, white characters and a potentiometer for contrast adjustment. The backlight can be connected through a jumper to the +5V supply, but I connected switched power from the GPIO interface board to the LED terminal of the jumper pins. This allows a power-off of the display backlight when the device is inactive.
Component side view of the LCD display. It’s always nice when a manufacturer clearly labels connections. The PCF8574 interface board had a bright LED on it that interfered with the video capture. I covered it with a blob of opaque silicone.
The only way to communicate the state of the switch that indicates whether the cube of random material has been removed from its platform and replaced is to transfer data from the python helper program to the main program written in C is through use of a file. The python program writes data to a file, and the C program reads it. To prevent excessive wear on the Raspberry Pi solid-state memory card, we use a memory-mapped file.
The Raspberry Pi has built-in Wi-Fi connectivity, so it’s easy to program a web interface to view the random numbers on a home network. In fact, some might decide to forego the LCD display and just use the web interface. The built-in Wi-Fi connectivity, the installed the Apache web server and PHP allows a web interface to view the random numbers on a home network with just one additional program. Web pages are served from the /var/www/html/prng/ folder, where the PHP source file, prng_log.php, is placed.
Web browser interface, accessed on my home network at http://192.168.1.61/prng/prng_log.php. The image is the image from which the latest random number is derived. The column entitled Von Neumann Trials indicates the quality of the raw data. On average, a 64-bit number will require 128 acquisitions of raw bit data for whitening. A good method for creating pin numbers is to select some middle decimal digits.
Random numbers are uniformly distributed, but the appearance of a uniform distribution is not a good test of randomness. That’s because a list of numbers in serial order, which is definitely not random, would produce a uniform distribution. Other non-random sequences, such as all even numbers followed by all odd numbers, and other not so obvious arrangement of numbers, will also show a uniform distribution while not being random.
The Diehard Test Suite, a collection of programs initially developed by computer scientist George Marsaglia is the acknowledged method for testing randomness. This updated test suit, now known as Dieharder, is maintained by Robert G. Brown of the Duke University Physics Department and his colleagues [8]. It’s freely available from the Linux repositories, but don’t run it on the Raspberry Pi! You need a fast desktop computer with a lot of memory for this!
Dieharder needs many random numbers for a valid test. I used 10 million for my randomness checks. Because it’s not possible to shake the cube of random material 10 million times to snap its image, I took the shortcut of doing these tests with one static image, so the results might be considered a worst-case effort. Also, Dieharder looks at 32-bit numbers. I modified the program to produce a simulation program to produce a file of 10 million random 32-bit decimal numbers, 10M_data.txt, with the proper header, and executed the following command to run the test suite:
For each test, Dieharder generates a p-value, which is a statistical measure of the rejection of the “null hypothesis” that the numbers aren’t random. The usual—and often misused measure—is that the null hypothesis is rejected when the p-value is greater than 0.05. Dieharder will also state plainly whether your numbers have passed the test. The results for my simulation are shown in Figure 9. Dieharder automatically runs two of the “runs” and “craps” tests. You can get an explanation of a certain test by executing:
Summary of the Dieharder randomness tests. All passed without comment, except for parking lot, which was noted as “weak.” In the parking lot test, unit circles are randomly placed in a 100×100 square. A circle is successfully parked if it does not overlap an existing successfully parked one. After 12,000 tries, the number of successfully parked circles should follow a certain normal distribution.
As every circuit experimenter knows, unexpected problems present themselves in the development of most electronic devices. One problem I had a difficult time in diagnosis was stray light reflections that reduced the contrast at one edge of the cube of random material. The light that produced the glare obviously originated from the illumination LEDs, so I tried moving their position inside the box. This didn’t really help. The eventual fix was to mask most of the area of the mirror, because reflection of the LED light from the over-sized mirror was the cause of the problem (Figure 10). There was still plenty of mirror left for proper imaging.
The finished project, displaying the two most recent 64-bit random numbers on the LCD display. The panel marking was done using a decal transfer process, as described in the text.
[2] M. Matsumoto and T. Nishimura, “Mersenne Twister: A 623-Dimensionally Equidistributed Uniform Pseudo-Random Number Generator”, ACM Transactions on Modeling and Computer Simulation, vol. 8, no. 1 (January, 1998), pp 3-30, doi:10.1145/272991.272995. https://dl.acm.org/doi/10.1145/272991.272995
[4] Landon Curt Noll, Robert G. Mende and Sanjeev Sisodiya, “Method for seeding a pseudo-random number generator with a cryptographic hash of a digitization of a chaotic system,” US Patent No. 5,732,138, March 24, 1998 (https://patents.google.com/patent/US5732138A )
[5] Joshua Liebow-Feeser, “Randomness 101: LavaRand in Production,” Cloudflare Web Site (https://blog.cloudflare.com/randomness-101-lavarand-in-production ).
If you’re working from home and have kids or a partner around, you’ve probably had them barge into your home office when you were in the middle of an important meeting. Do you wish your family would visit you at more convenient times during the work day? In this tutorial, we’ll set up a method to show your work status (busy or available or “in a meeting”) on a Raspberry Pi LCD screen you can hang outside your door.
In order to fit the wires and the LCD screen with the I2C backpack into the case, I slightly bent the pins of the I2C backpack outwards and then inserted the 4 female-to-female wires.
Optional: As a side project, I’ve included the code for a digital clock display. After running the lcd_disp.py code, in the terminal now enter
If the time displayed on your LCD screen is incorrect, go to your Raspberry Pi Configuration (as in Step 2), Localisation tab and click “Set Timezone” to your time zone.
Code notes abouttest_messages.pyThe command mylcd.lcd_display_screen refers to the file i2c_lcd_driver.py that was included in the github package https://github.com/carolinedunn/WFH_LCD
mylcd.lcd_display_string(“Welcome to”, 1) instructs the Pi to display “Welcome to” on the first line of the LCD display. The first parameter is the text and the second parameter is the line number for the LCD screen. If your string (1st parameter) is longer than 16 characters only the first 16 characters will display on your LCD screen.
Code notes aboutstatus.pyThis Python code creates APIs that you can call from another device on your network. To test this, go to your desktop computer, type in the hostname of your Pi followed by “:5000/api/busy” (ex: http://raspberrypi:5000/api/busy) to see the LCD screen text change to “Status: Busy”
For example, if your Pi’s hostname is raspberrypi (the default hostname), enter the following URL in the browser of your desktop computer “http://raspberrypi:5000/api/away” and the LCD screen text will now read“Status: Away”
At this point, you can customize the LCD text functions to statuses that are appropriate for your purposes, making note of the API names that you may change, add, or delete.
We have used Liquid Crystal Displays in the DroneBot Workshop many times before, but the one we are working with today has a bit of a twist – it’s a circle! Perfect for creating electronic gauges and special effects.
LCD, or Liquid Crystal Displays, are great choices for many applications. They aren’t that power-hungry, they are available in monochrome or full-color models, and they are available in all shapes and sizes.
Waveshare actually has several round LCD modules, I chose the 1.28-inch model as it was readily available on Amazon. You could probably perform the same experiments using a different module, although you may require a different driver.
Open the Arduino folder. Inside you’ll find quite a few folders, one for each display size that Waveshare supports. As I’m using the 1.28-inch model, I selected theLCD_1inch28folder.
Once you do that, you can open your Arduino IDE and then navigate to that folder. Inside the folder, there is a sketch file namedLCD_1inch28.inowhich you will want to open.
When you open the sketch, you’ll be greeted by an error message in your Arduino IDE. The error is that two of the files included in the sketch contain unrecognized characters. The IDE offers the suggestion of fixing these with the “Fix Encoder & Reload” function (in the Tools menu), but that won’t work.
The error just seems to be with a couple of the Chinese characters used in the comments of the sketch. You can just ignore the error, the sketch will compile correctly in spite of it.
Unfortunately, Waveshare doesn’t offer documentation for this, but you can gather quite a bit of information by reading theLCD_Driver.cppfile, where the functions are somewhat documented.
The TFT_eSPI library is ideal for this, and several other, displays. You can install it through your Arduino IDE Library Manager, just search for “TFT_eSPI”.
A great demo code sample is theAnimated_dialsketch, which is found inside theSpritesmenu item. This demonstration code will produce a “dial” indicator on the display, along with some simulated “data” (really just a random number generator).
One of my favorite sketches is the Animated Eyes sketch, which displays a pair of very convincing eyeballs that move. Although it will work on a single display, it is more effective if you use two.
The GC9A01 LCD module is a 1.28-inch round display that is useful for instrumentation and other similar projects. Today we will learn how to use this display with an Arduino Uno and an ESP32.
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.
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.
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.