The 1wire bus supports various low speed digital devices and is supported in Linux on the Raspberry Pi.

NB All DS18B20 thermometer ICs from non-reputable dealers are fake.

Edit boot/config.txt to assign gpio4 for 1wire.

dtoverlay=w1-gpio,gpiopin=4

Reboot and after load driver.

modprobe w1_gpio

These are the GPIO header pin assignments for the 1 wire bus.

The relevant pins on the Pi header are as follows.

                +---P1---+
3V3             01      02 5V
GPIO0/GPIO2     03 A/A+ 04 5V
GPIO1/GPIO3     05 B/B+ 06 GND
GPIO4           07 2    08 GPIO14/TX
                ..      ..

NB. The 1 wire data line must pulled high via 4K7 to 3V3 power.

TO-92
+-------+
| 1 2 3 |
+-------+
  | | |
  | | |
  
1 GROUND
2 DATA
3 POWER

ROM 28 FF D6 BD 60 14 04 95 (clone)

modprobe w1_therm
cat /sys/bus/w1/devices/28-041460bdd6ff/w1_slave 
8f 01 55 00 7f ff 0c 10 a0 : crc=a0 YES
8f 01 55 00 7f ff 0c 10 a0 t=24937

BLACK  GROUND
YELLOW DATA
RED    POWER

ROM 28 FF CB AA 72 15 02 A7 (clone)

This module re-orders the pins so beware.

+-------+
|DS18B20|
|       |
+-G R Y-+
  | | |
  
G GROUND
R POWER
Y DATA

ROM 28 FF 51 73 A8 15 03 12 (clone)

DATA is pulled up via a 4K7 resistor and an LED. The LED will flash during communication with the chip.

+-------+
| 1 2 3 |
+-------+
  | | |
  | | |
  
1 GROUND
2 DATA
3 NC

modprobe w1_ds2431
echo "hello world" > /sys/bus/w1/devices/2d-00000de5d608/eeprom
cat /sys/bus/w1/devices/2d-00000de5d608/eeprom
hello world

DS18B20 thermometer data-sheet

DS2431 EEPROM data-sheet

Fake DS18B20