Overview

The i2c node enables communication with I2C (Inter-Integrated Circuit) devices. I2C is a multi-device bus protocol using just two wires (SDA and SCL) to connect multiple sensors, displays, EEPROM, and other peripherals to your Raspberry Pi.

127

Max Devices

Wires (SDA+SCL)

400kHz

Fast Mode

3.3V

Logic Level

Raspberry Pi I2C Pins

I2C Bus 1 (Default)

SDA (Data) GPIO 2 (Pin 3)

SCL (Clock) GPIO 3 (Pin 5)

Enable I2C

sudo raspi-config
# Interface Options → I2C → Enable

# Or add to /boot/config.txt:
dtparam=i2c_arm=on

Properties

Property	Type	Required	Default	Description
address	number	Yes	-	Device I2C address (0x00-0x7F)
bus	number	No	1	I2C bus number
command	string	No	"read"	"read", "write", "scan"
register	number	No	-	Register address to read/write
count	number	No	1	Number of bytes to read

Inputs

Read Operation

{
  "payload": {
    "command": "read",
    "register": 0x00,
    "count": 2
  }
}

Write Operation

{
  "payload": {
    "command": "write",
    "register": 0x01,
    "data": [0x80, 0x03]
  }
}

Outputs

Read Response

{
  "payload": {
    "data": [0x1A, 0x3C],
    "buffer": "<Buffer 1a 3c>"
  },
  "address": 104,
  "register": 0
}

Scan Response

{
  "payload": [35, 60, 104],
  "devices": ["0x23", "0x3C", "0x68"]
}

Common I2C Devices

Device	Address	Type	Notes
BME280	0x76 / 0x77	Temp/Humidity/Pressure	SDO pin selects address
SSD1306	0x3C / 0x3D	OLED Display	128x64 / 128x32 pixels
MPU6050	0x68 / 0x69	Accelerometer/Gyroscope	AD0 pin selects address
BH1750	0x23 / 0x5C	Light Sensor	ADDR pin selects address
PCF8574	0x20-0x27	GPIO Expander	8 extra I/O pins
ADS1115	0x48-0x4B	ADC	16-bit, 4 channels

Example: Scan I2C Bus

Find all connected I2C devices and their addresses.

[
  {
    "id": "scan-trigger",
    "type": "inject",
    "payload": "{ "command": "scan" }",
    "payloadType": "json"
  },
  {
    "id": "i2c-scan",
    "type": "i2c",
    "bus": 1,
    "address": ""
  },
  {
    "id": "display",
    "type": "debug",
    "name": "I2C Devices"
  }
]

Tip: Run i2cdetect -y 1 in terminal to verify I2C devices.

Troubleshooting

No devices detected

Enable I2C: sudo raspi-config → Interface Options → I2C
Check wiring: SDA to SDA, SCL to SCL
Verify power: Most devices need 3.3V
Install tools: sudo apt install i2c-tools

Permission denied errors

sudo usermod -a -G i2c $USER
sudo reboot

Intermittent communication failures

Add 4.7kΩ pull-up resistors on SDA and SCL
Keep wires short (<30cm for best reliability)
Use shielded cable for noisy environments
Reduce I2C speed if using long wires

Related Nodes

bme280

I2C temperature sensor

spi

Alternative serial protocol

bh1750

I2C light sensor