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node_modules/i2c-bus/doc/raspberry-pi-i2c.md

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+## Configuring I2C on the Raspberry Pi
+
+This guide assumes that release 2015-01-31 or later of the Raspbian Operating
+System is being used.
+
+An I2C bus is broken out to pins 3 (SDA) and 5 (SCL) on the P1 header. The
+number of steps that need to be performed to configure this I2C bus for usage
+by user `pi` on Raspbian without root privileges is highly dependent in the
+version of Raspbian being used.
+
+### Configuring I2C with raspi-config
+
+With Raspbian Jessie 2015-11-21 or later the complete configuration can be
+performed with the `raspi-config` software configuration tool which can be run
+from a terminal window as follows:
+
+```
+sudo raspi-config
+```
+
+In the `raspi-config` user interface navigate to `Interfacing Options >> I2C`
+and answer the question `"Would you like the ARM I2C interface to be enabled?"`
+with `<Yes>`. After the next reboot user `pi` will be able to use the I2C bus
+without root privileges.
+
+### Configuring I2C Manually
+
+On older versions of Raspbian (prior to Raspbian Jessie 2015-11-21) the
+`raspi-config` tool can still be used to configure the I2C bus, but additional
+steps typically need to be performed.
+
+#### Step 1 - Enable I2C
+
+To enable I2C ensure that `/boot/config.txt` contains the following line:
+
+```
+dtparam=i2c_arm=on
+```
+
+#### Step 2 - Enable user space access to I2C
+
+To enable userspace access to I2C ensure that `/etc/modules` contains the
+following line:
+
+```
+i2c-dev
+```
+
+#### Step 3 - Setting the I2C baudrate
+
+The default I2C baudrate is 100000. If required, this can be changed with the
+`i2c_arm_baudrate` parameter. For example, to set the baudrate to 400000, add
+the following line to `/boot/config.txt`:
+
+```
+dtparam=i2c_arm_baudrate=400000
+```
+
+#### Step 4 - I2C access without root privileges
+
+If release 2015-05-05 or later of the Raspbian Operating System is being used,
+this step can be skipped as user `pi` can access the I2C bus without root
+privileges.
+
+If an earlier release of the Raspbian Operating System is being used, create a
+file called `99-i2c.rules` in directory `/etc/udev/rules.d` with the following
+content:
+
+```
+SUBSYSTEM=="i2c-dev", MODE="0666"
+```
+
+This will give all users access to I2C and sudo need not be specified when
+executing programs using i2c-bus. A more selective rule should be used if
+required.
+
+#### Step 5 - Reboot the Raspberry Pi
+
+After performing the above steps, reboot the Raspberry Pi.
+