# 1-Wire interface

<abstract>
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp.
This article explains how to use it on the CM3-HOME-B and CM3-HOME-F boards
</abstract>

<a href="https://en.wikipedia.org/wiki/1-Wire" target="_blank" class="btn btn-default" role = "button">
<span class="glyphicon glyphicon-question-sign" aria-hidden="true"></span> What is a 1-wire bus ? </a>

The most popular use of 1-wire bus is to use the Dallas DS18B20 temperature sensors. The image below 
illustrates how to wire it on the screw terminals available on the CM3-Home board. It is possible to wire
more than one sensor.

<img src="./1wire.jpg" class="img-responsive center-block" width="80%">

As depicted on the @article='CM3-HOME_schematic', the 1-wire data line is interfaced through a dedicated buffer in order to allow a more robust bus, therefore it doesn't require a pullup.

## Configuration

To use the 1-wire sensor port add this lines to __config.txt__ file and reboot:

	# Enable the 1-wire bus 
	dtoverlay=w1-gpio,gpiopin=16

The sensor wired are automatically detected by the Linux Kernel and a new directory is created on the folder __/sys/bus/w1/devices__ for each of them.

	$ ls /sys/bus/w1/devices/
	28-000006c423d3

In this case a temperature sensor with id=28-000006c423d3 has been detected. To read the temperature value type:

	$ cat /sys/bus/w1/devices/28-000006c423d3/w1_slave 
	a4 01 4b 46 7f ff 0c 10 da : crc=da YES
	a4 01 4b 46 7f ff 0c 10 da t=26250