==== 1wire bus ====
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{{:interfaces:1wire.jpg?100}}
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{{:interfaces:1wire-2.jpg?100}}
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{{:interfaces:keyes.jpg?100}}
</wrap>

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.
=== Raspberry Pi ===

Edit boot/config.txt to assign gpio4 for 1wire.
<code>
dtoverlay=w1-gpio,gpiopin=4
</code>

Reboot and after load driver.
<code>
modprobe w1_gpio
</code>

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

^Pin ^Name  ^Function |
| 1  | 3V3 | POWER|
| 6  | GND| GROUND |
| 7  | GPIO4 | DATA|

The relevant pins on the Pi header are as follows.
<code>
                +---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
                ..      ..
</code>

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


=== DS18B20 thermometer  ===

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{{:interfaces:ds18b20.jpg?50}}
</wrap>

<code>
TO-92
+-------+
| 1 2 3 |
+-------+
  | | |
  | | |
  
1 GROUND
2 DATA
3 POWER

ROM 28 FF D6 BD 60 14 04 95 (clone)
</code>

<code>
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
</code>

=== DS18B20 water-proof thermometer ===

<wrap right>
{{interfaces:tempprobe.jpg?50}}
</wrap>

<code>
BLACK  GROUND
YELLOW DATA
RED    POWER

ROM 28 FF CB AA 72 15 02 A7 (clone)
</code>

=== KEYES KY-001 DS18B20 thermometer module ===

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{{:interfaces:keyes2.jpg?50}}
</wrap>

This module re-orders the pins so beware.

<code>
+-------+
|DS18B20|
|       |
+-G R Y-+
  | | |
  
G GROUND
R POWER
Y DATA

ROM 28 FF 51 73 A8 15 03 12 (clone)
</code>

DATA is pulled up via a 4K7 resistor and an LED. The LED will flash
during communication with the chip.
=== DS2431 EEPROM ===
<code>
+-------+
| 1 2 3 |
+-------+
  | | |
  | | |
  
1 GROUND
2 DATA
3 NC
</code>

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

=== Resources ===

[[https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf|DS18B20 thermometer data-sheet]]

[[https://datasheets.maximintegrated.com/en/ds/DS2431.pdf|DS2431 EEPROM data-sheet]]

[[https://github.com/cpetrich/counterfeit_DS18B20|Fake DS18B20]]