Table of Contents
STM_5: Using LCD Display
Alphanumerical LCD is one of the most popular output devices in the Embedded and IoT. Using LCD with predefined line organisation (here, 2 lines, 16 characters each) is as simple as sending a character's ASCII code to the device. This is so much simpler than in the case of the use of dot-matrix displays, where it is necessary to use fonts. The fixed organisation LCD has limits; here, only 32 characters can be presented to the user simultaneously. ASCII presents a limited set of characters, but many LCDs can redefine character maps (how each letter, digit or symbol looks). This way, it is possible to introduce graphics elements (i.e. frames), special symbols and letters.
In this scenario, you will learn how to handle easily LCD to present information and retrieve it visually with a webcam.
Prerequisites
Familiarise yourself with a hardware reference. LCD of this type can be connected to the microcontroller with 8 or 4 lines of data, RS - register select, R/#W - read/write, and EN - synchronisation line. In our lab equipment, the LCD is controlled with 6 GPIOs. We use 4 lines for data and because We don't read anything from the LCD the R/#W is connected to the ground. Details can be found in Table 1: STM32WB55 Node Hardware Details on the STM32 laboratory hardware reference page.
You are going to use a library to handle the LCD. It means you need to add it to your platformio.ini file. Use the template provided in the hardware reference section and extend it with the library definition:
lib_deps = arduino-libraries/LiquidCrystal@^1.0.7
Suggested Readings and Knowledge Resources
Hands-on Lab Scenario
Task to be implemented
Draw “Hello World” in the upper line of the LCD and “Hello IoT” in the lower one.
Start
Check if you can see a full LCD in your video stream. Book a device and create a dummy Arduino file with void setup()… and void loop()….
Steps
Step 1
Include the library in your source code:
#include <LiquidCrystal.h>
Step 2
Declare GPIOs controlling the LCD, according to the hardware reference:
const int rs = PC5, en = PB11, d4 = PB12, d5 = PB13, d6 = PB14, d7 = PB15;
Step 3
Declare an instance of the LCD controller class and preconfigure it with appropriate control GPIOs:
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
Step 4
Initialise class with display area configuration (number of columns, here 16 and rows, here 2):
lcd.begin(16, 2);
Step 5
Implement your algorithm. The most common class methods that will help you are listed below:
.clear()- clears all content;.setCursor(x,y)- set cursor, writing will start there;.print(contents)- prints text in the cursor location; note there are many overloaded functions, accepting various arguments, including numerical.
A simple example can be the Hello World:
lcd.print("hello, world!");
Result validation
You should be able to see “Hello World” and “Hello IoT” on the LCD now.
