in /boot/config.txt (or use raspi-config)
dtparam=i2c_arm=on
reboot
On a Pi5, also disable the onboard rtc:
dtparam=rtc=off
sudo apt-get install python-smbus i2c-tools
sudo i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- 51 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- --
to /boot/config.txt
dtoverlay=i2c-rtc,rv3032
reboot
sudo i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- --
$ sudo dmesg | grep rtc [ 2.837650] rtc-rv3032 1-0051: registered as rtc0 [ 2.839127] rtc-rv3032 1-0051: setting system clock to 2025-02-01T05:17:05 UTC (1738387025)
sudo apt-get -y remove fake-hwclock & sudo update-rc.d -f fake-hwclock remove & sudo systemctl disable fake-hwclock
edit
sudo nano /lib/udev/hwclock-set
comment these lines:
(7,8, 9)
if [ -e /run/systemd/system ] ; then exit 0 fi
29:
/sbin/hwclock --rtc=$dev --systz --badyear
32:
/sbin/hwclock --rtc=$dev --systz
reboot
The folks that designed the DS3231 were very kind and made the temperature registers user-readable, so we can use it as a thermometer! How neat is that! The temperature is stored in registers 0x11 and 0x12 and is reported in 0.25ºC increments, though keep in mind the sensor is only accurate to ±3ºC. This forum post includes a sample python script that reads those registers and displays the output. It needs to be run with root privileges, and it will briefly unload the RTC kernel module in order to access the device, though this shouldn't matter given how quickly it runs.
lm-sensors includes a driver that can read the DS3231's temperature sensor. Install the lm-sensors package, then run 'sensors'.
rpi_volt-isa-0000 Adapter: ISA adapter in0: N/A cpu_thermal-virtual-0 Adapter: Virtual device temp1: +31.4°C rv3032-i2c-1-51 Adapter: Synopsys DesignWare I2C adapter temp1: +21.3°C rp1_adc-isa-0000 Adapter: ISA adapter in1: 950.00 mV in2: 2.39 V in3: 1.40 V in4: 1.43 V temp1: +36.9°C
$cat /sys/class/i2c-dev/i2c-1/device/1-0051/hwmon/hwmon3/temp1_input 21312