ESP32-C3 I2C LCD Simulator: Wiring, Code and a Live Circuit
This is a 16 by 2 character LCD with a PCF8574 I2C backpack, wired to an ESP32-C3 DevKitM-1 and running live: the first line names the board and the second counts the seconds since reset. It uses the LiquidCrystal_I2C library, so four wires replace the sixteen of a bare LCD.
SDA goes to GPIO 8 and SCL to GPIO 9. The display needs 5 V, so on the 3.3 V ESP32-C3 it is powered from 5V, and the I2C lines need care on a real bench, as the wiring notes explain.
- 3.3 V logic
- Library: LiquidCrystal_I2C.h
- I2C address 0x27
- Powered from 5V
Wiring the I2C LCD to the ESP32-C3
Every connection in the circuit above, with the board’s own pin names.
| I2C LCD pin | ESP32-C3 pin | Why |
|---|---|---|
| VCC | 5V | The LCD glass needs 5 V for its contrast; at 3.3 V most modules show nothing. |
| GND | GND | Common ground. |
| SDA | GPIO 8 | I2C data. |
| SCL | GPIO 9 | I2C clock. |
On the ESP32-C3, Wire.begin() uses GPIO 8 for SDA and GPIO 9 for SCL, the Arduino core’s choice; Wire.begin(sda, scl) moves the bus to any two other pins. The backpack runs from 5 V and carries 4.7 k pull-ups on SDA and SCL, so on a real ESP32-C3 those lines idle at 5 V. Either remove the backpack’s two pull-up resistors and add 4.7 k pull-ups to 3V3, or put a two-channel level shifter between them. The simulator does not punish it; a real ESP32-C3 (RISC-V) may.
Pins to leave alone on the ESP32-C3
GPIO 8 carries the onboard LED and GPIO 9 is the BOOT button, and both are also the default I2C pins. GPIO 2, 8 and 9 are strapping pins, and only GPIO 0 to 4 can read an analog voltage.
On a real bench
The ESP32-C3 DevKitM-1 is small enough to sit on one breadboard with room for the I2C LCD beside it. Its USB port goes through a USB-to-serial chip; the cheaper SuperMini boards use the C3’s own USB, where Serial needs USB CDC on boot turned on in the IDE.
The code
The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
// A 16 x 2 display behind a PCF8574 backpack at 0x27.
// SDA GPIO 8, SCL GPIO 9.
LiquidCrystal_I2C lcd(0x27, 16, 2);
void setup() {
Serial.begin(115200);
lcd.init();
lcd.backlight();
lcd.setCursor(0, 0);
lcd.print("ESP32-C3");
Serial.println("LCD ready");
}
void loop() {
lcd.setCursor(0, 1);
lcd.print("Seconds: ");
lcd.print(millis() / 1000);
lcd.print(" "); // clears the tail of a shorter number
delay(250);
}
LiquidCrystal_I2C lcd(0x27, 16, 2) names the backpack’s address and the size of the display. init() wakes the HD44780 controller behind the backpack in four-bit mode, and backlight() turns the LED on, which is a bit in the backpack, not in the display.
setCursor(column, row) counts from zero, so (0, 1) is the start of the second line. print() writes text there and moves the cursor along, the way Serial.print() does.
The three spaces after the number overwrite whatever a longer number left behind. Calling clear() every time would do the same and make the display flicker, because clear() takes about 2 ms and blanks the whole panel. Serial.begin(115200) opens the serial monitor. Serial is UART0, at 115200 baud in this sketch.
Common mistakes with the I2C LCD on the ESP32-C3
The wrong address
Backpacks with the PCF8574T chip answer at 0x27; those with the PCF8574AT answer at 0x3F. The screen lights but shows nothing when the address is wrong. Run an I2C scanner, or set the part’s address property in the editor to match yours.
Contrast turned all the way down
A row of solid blocks, or nothing at all with the backlight on, is usually the blue trimmer on the backpack. Turn it until the text appears. In the simulator the part has a contrast property for the same thing.
Powering it from 3V3
The backlight comes on, so it looks wired, but the liquid crystal needs about 5 V of drive for contrast and the characters stay invisible. Use 5V.
Questions and answers
Can I simulate a 16x2 I2C LCD with an ESP32-C3 DevKitM-1?
Yes. The circuit at the top of this page is an ESP32-C3 DevKitM-1 with a 16x2 I2C LCD, running in your browser on a simulated ESP32-C3 (RISC-V). The characters the sketch prints appear on the simulated panel, backlight and contrast included. Press Run it in the editor to change the wiring or the code; it is free and needs no account.
Where do SDA and SCL go on the ESP32-C3?
On the ESP32-C3, Wire.begin() uses GPIO 8 for SDA and GPIO 9 for SCL, the Arduino core’s choice; Wire.begin(sda, scl) moves the bus to any two other pins.
Is a 5 V I2C LCD safe on the ESP32-C3?
Power is fine from 5V. The I2C lines are the risk: the backpack pulls them up to 5 V. On a real board use a level shifter, or move the pull-ups to 3.3 V.
How do I find the LCD’s I2C address?
Upload an I2C scanner sketch: it calls Wire.beginTransmission() on every address and prints the ones that answer. The two you will almost always see are 0x27 and 0x3F.
Build your own I2C LCD project
Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.