4.1 Print Message
Every example so far has reported back through the Serial Monitor, which means the board only has something to say while it is tethered to a computer. This one changes that: the kit's 16x2 LCD gives the board a screen of its own, and a message printed there stays on it whether the computer is watching or not.
The wiring is the easiest in the whole kit. The LCD is a Qwiic module, so one cable does everything.
In this documentation you will learn:
- How to connect the 16x2 LCD with a single Qwiic cable.
- What the purple I2C LCD adapter on the back of the display is for.
- How to initialize a display and turn on its backlight.
- How to put text where you want it with
setCursor(), and why counting from zero matters. - Why only 16 characters fit on a row, and what happens to the seventeenth.
- What to do when the screen glows but stays empty, the one fault that catches everybody.
Hardware required:
- 1x Soldered NULA MINI board
- 1x Breadboard
- 1x 16x2 LCD display with I2C adapter
- 1x Qwiic cable
- 1x USB-C cable
Putting the components together
1. Insert the NULA MINI board on the breadboard
Push the board into one end of the breadboard so that its two rows of pins sit on either side of the centre channel, with the chip facing down.
2. Plug the Qwiic cable into the board
The NULA MINI has one Qwiic connector, on the edge of the board between the USER and RST buttons. It is the white connector marked qwiic on the silkscreen. Push the cable in until it clicks.
- and +. That one is the battery connector, and a Qwiic cable will not fit it.If you would like to see exactly which connector this is on a bare board, it is highlighted here:
3. Plug the other end into the display
Turn the display over and you will find a purple board screwed to its back, silkscreened I2C LCD ADAPTER. It carries two Qwiic connectors, one at each end. Plug the free end of the cable into either one. They are wired together, and the spare exists so you can chain another module onwards.
SCL, SDA, 5V and GND. That is the same connection brought out to solder pins, for boards that have no Qwiic socket. You do not need it here. The cable does the same job.4. Plug in the USB-C cable
Connect the board to your computer. The purple PWR light comes on and the display's backlight lights up blue, but the screen itself stays empty, because you have not uploaded anything to the board yet.
What the adapter board is for
Look closely at the green display board and you will count 16 pins along its top edge, labelled VSS, VDD, V0, RS, RW, E, D0 through D7, A and K. That is the native interface of the HD44780, the controller chip that has driven displays like this since the 1980s. Wiring it directly means fourteen or so connections, and you would spend this whole example pushing jumper wires into a breadboard.
The purple adapter board does that job for you. It sits on those 16 pins permanently and talks to your board over just two wires instead.
Those two wires are the I2C bus, the same one the ultrasonic sensor used in example 3.1: SDA carries the data and SCL provides the clock that keeps both ends in step. Several modules can share one pair of wires, each answering to its own address, which is why this board has I2C ADDR 0X20 printed on it. 0x20 is the number this display answers to.
LCD lcd(16, 2); needs no pin numbers, exactly as Ultrasonic_Sensor hc; needed none in 3.1. On the NULA MINI the I2C lines are permanently wired to IO6 and IO7 and are not even brought out to the pin headers, so there is nothing to choose. The library already knows the address, so begin() takes no arguments either.You may also spot three small pads marked A0, A1 and A2 near the SOLDERED logo. Bridging them with solder changes the address, up to 0x27. You would only ever do that to put two of these displays on one cable. Leave them alone.
Installing the library
This example needs the Soldered LCD library. If you followed Setting up the Arduino environment you already have it. If not, open Tools → Manage Libraries, search for Soldered LCD, and install the one published by Soldered Electronics.
fatal error: LCD-SOLDERED.h: No such file or directory, you have installed the wrong one of the two.Rows, columns, and counting from zero
The display is a grid: 16 characters across, 2 rows down. lcd.setCursor(column, row) chooses where the next thing you print will land, and both numbers start at zero:
lcd.setCursor(0, 0)is the very first character of the top row.lcd.setCursor(0, 1)is the very first character of the bottom row.
So the rows are numbered 0 and 1, not 1 and 2, and the columns run 0 to 15. Asking for row 2 on a two-row display gets you nothing at all rather than an error, which is a confusing way to lose ten minutes.
The 16-character limit is worth taking seriously, because the display does not wrap. Print a nineteen-character string and you get the first sixteen characters and nothing else. The rest is simply thrown away, with no warning. Both messages in this example are twelve characters long, so both fit comfortably:
column: 0123456789012345
row 0: Hello, NULA!
row 1: Let's start!
Everything happens once
One last thing to notice before the code: every instruction in this example sits inside setup(), and loop() is completely empty.
That is deliberate. setup() runs once when the board starts, and loop() then runs forever, but there is nothing here that needs repeating. An LCD holds whatever it was last told to show, without being reminded, so printing the message once is enough. It stays on the screen until you cut the power or press RST, which restarts the sketch and prints it again.
Code
/**
**************************************************
*
* @file 4.1_Print_Message.ino
* @brief Example that shows how to display a message on an LCD screen.
* The LCD is controlled using the Soldered LCD library.
* This example demonstrates the basics of initializing the display and printing text.
* For details, connection diagram and more, check out the example documentation at: <link placeholder>
* @author Soldered
***************************************************
*/
#include "LCD-SOLDERED.h" // Include the Soldered LCD library
/*
Create an LCD object with 16 columns and 2 rows.
These numbers correspond to the width and height of the display.
*/
LCD lcd(16, 2);
void setup() {
/*
Initialize the LCD display and turn on the backlight (if supported by your module).
*/
lcd.begin();
lcd.backlight();
/*
Clear the display to ensure a clean start.
*/
lcd.clear();
/*
Set the cursor to the first column of the first row.
Then print a simple message on the LCD screen.
*/
lcd.setCursor(0, 0);
lcd.print("Hello, NULA!");
/*
Move to the second line and print another message. Keep in mind that this display fits exactly 16 characters per row,
so anything longer is simply cut off at the edge. Count the characters of your own messages before printing them.
*/
lcd.setCursor(0, 1);
lcd.print("Let's start!");
}
void loop() {
/*
Nothing needs to run repeatedly in this example.
The message remains visible until the board is reset or powered off.
*/
}
lcd.clear() wipes anything left over from a previous sketch. Without it you can end up reading a mixture of the old message and the new one, because whatever was on the display stayed there through the upload.What you should see
Upload the sketch. Within a second of the board restarting, both lines appear, the same build as the photo above, now with something on the screen:
There is no Serial Monitor output this time. The sketch never calls Serial.begin(), because the display is the output. Press RST and the two lines blink off and back on as the sketch runs again.
If the backlight is on but the screen is empty
This is the single most common problem with these displays, and it is not a fault in your code.
The characters are being sent correctly, but the display's contrast voltage is set so low that they are invisible against the backlight. The fix is a small trimmer potentiometer on the adapter board, marked CONTRAST:
With the board powered and the sketch running, turn that trimmer slowly through its full range with a small flat screwdriver. At one end you get a blank blue screen; at the other, a row of solid dark blocks. Your text is somewhere in between. Stop where the characters look crisp. You only ever need to do this once.
Soldered NULA Mini ESP32C6. The library asks for the board's default I2C pins, and a different board selection sends the data to the wrong pins while still compiling and uploading perfectly happily. After that, reseat both ends of the Qwiic cable until each one clicks.Try it yourself: change one of the messages to something longer than sixteen characters and upload again. You will see it clipped at exactly the sixteenth character, which is a quicker way to learn the limit than counting.
Full example
Check out the full example code on the link below:
4.1_Print_Message.ino
Example that initializes the Qwiic 16x2 LCD and prints a static two-line message using the Soldered LCD library.