Overview
The lcd_i2c node drives HD44780-compatible LCD displays through an I2C backpack
(typically PCF8574-based). These character LCD modules are popular for displaying status messages, sensor readings,
and simple menus in IoT projects. The I2C interface reduces wiring from 16 pins down to just 4 (VCC, GND, SDA, SCL).
Properties
| Property | Type | Default | Options | Description |
|---|---|---|---|---|
| i2cBus | select | "/dev/i2c-1" | /dev/i2c-0, /dev/i2c-1 | I2C bus device path |
| address | select | "0x27" | 0x27, 0x3f | I2C address of the LCD backpack |
| rows | select | "2" | 1, 2, 4 | Number of display rows |
| cols | select | "16" | 16, 20 | Number of display columns |
| backlight | boolean | true | - | Enable LCD backlight on startup |
| cursorBlink | boolean | false | - | Enable blinking cursor at write position |
Input
// Simple string - displays on line 1
msg.payload = "Hello World!";
// Multi-line with array
msg.payload = [
"Temperature: 23C",
"Humidity: 65%"
];
// Advanced: specify line and column
msg.payload = {
"line1": "Temp: 23.5C",
"line2": "Humid: 65.2%",
"backlight": true
};Output
{
"payload": true,
"topic": "lcd/status",
"_lcd": {
"address": "0x27",
"rows": 2,
"cols": 16,
"backlight": true
}
}Wiring / Connection Diagram
Raspberry Pi I2C LCD Module
+-----------+ +------------------+
| | | PCF8574 Backpack |
| 5V (2) +------------+ VCC |
| | | |
| SDA (3) +------------+ SDA |
| | | |
| SCL (5) +------------+ SCL |
| | | |
| GND (6) +------------+ GND |
| | | |
+-----------+ | +----------+ |
| | HD44780 | |
| | 16x2 or | |
| | 20x4 | |
| +----------+ |
+------------------+
Address selection (solder jumpers on backpack):
- A0, A1, A2 all open: 0x27 (default)
- A0, A1, A2 all closed: 0x20
- Some modules default to 0x3F
Tip: Run i2cdetect -y 1 to confirm the LCD
address. Common addresses are 0x27 and 0x3F depending on the PCF8574 variant used.
Example Use Cases
Sensor Data Display
Show live temperature and humidity readings on a 16x2 LCD.
// Function node: format sensor data for 16x2 LCD
var temp = msg.payload.temperature.toFixed(1);
var humid = msg.payload.humidity.toFixed(1);
msg.payload = [
"Temp: " + temp + "C",
"Humid: " + humid + "%"
];
return msg;System Status Dashboard (20x4)
Display system information on a 20x4 character LCD.
// Function node: build 4-line status display
var ip = flow.get("ipAddress") || "No Network";
var uptime = flow.get("uptime") || "0h";
var cpu = flow.get("cpuTemp") || "--";
var nodes = flow.get("activeNodes") || 0;
msg.payload = {
"line1": "EdgeFlow v2.1.0 ",
"line2": "IP: " + ip,
"line3": "Up:" + uptime + " CPU:" + cpu + "C",
"line4": "Nodes: " + nodes + " active"
};
return msg;Alert Notification with Backlight Control
Flash the backlight and display alert messages when thresholds are exceeded.
// Function node: alert with backlight flash
var temp = msg.payload.temperature;
var threshold = 35;
if (temp > threshold) {
msg.payload = {
"line1": "!! WARNING !!",
"line2": "Temp: " + temp.toFixed(1) + "C HIGH",
"backlight": true
};
} else {
msg.payload = {
"line1": "System Normal",
"line2": "Temp: " + temp.toFixed(1) + "C",
"backlight": true
};
}
return msg;Common Use Cases
Sensor Readouts
Display live temperature, humidity, and pressure values
System Status
Show IP address, uptime, and device health on a local display
Alert Notifications
Visual warnings with backlight flashing for threshold alerts
Menu Interfaces
Simple selection menus with button navigation on 20x4 displays