enable-i2c

Source: Enable I2C Interface on the Raspberry Pi

Why

The default Raspberry Pi (and reTerminal) image has I2C disabled. It must be enabled before any I2C devices work — including the Grove Base Hat ADC and AHT20 sensor.

Method 1: raspi-config (command line)

sudo raspi-config

Navigate: Interface Options → I2C → Yes → reboot when prompted.

Method 2: GUI

Menu > Preferences > Raspberry Pi Configuration → Interfaces tab → set I2C to Enabled → OK → reboot.

Install I2C tools

sudo apt-get update
sudo apt-get install -y python3-smbus i2c-tools

Verify I2C is loaded

lsmod | grep i2c_
# Look for: i2c_bcm2708

Detect connected I2C devices

i2cdetect -y 1    # use bus 1 (all Pi models except original B Rev 1)
i2cdetect -y 0    # only for original Model B Rev 1

Output example:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
...
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

• Hex address = device connected at that address
• UU = address in use by a kernel driver
• -- = nothing detected

Shutdown before connecting hardware:

sudo halt

See Also

• I2C concept
• Serial Protocols topic
• GPIO and reTerminal topic (grove.adc requires I2C enabled)
• grove-adc source