Merge branch 'pull-request-1-from-github' into 'master'

Pull request 1 from github

See merge request MSO-SW/drivers/raspberry-pi/raspberry-pi-i2c-scd4x!9

Author: psachs

README.md

@@ -18,12 +18,12 @@ Setup Guide
 Your sensor has the four different connectors: VCC, GND, SDA, SCL. Use
 the following pins to connect your SCD4x:
 
- *SCD4x*  |    *Raspberry Pi*
- :------: | :------------------:
-   VCC    |        Pin 1
-   GND    |        Pin 6
-   SDA    |        Pin 3
-   SCL    |        Pin 5
+ *SCD4x*  |    *Raspberry Pi*    | *Jumper Wire*
+ :------: | :------------------: | :-----------:
+   VCC    |        Pin 1         |      Red
+   GND    |        Pin 6         |     Black
+   SDA    |        Pin 3         |     Green
+   SCL    |        Pin 5         |     Yellow
 
 <center><img src="images/GPIO-Pinout-Diagram.png" width="900px"></center>
 
@@ -66,12 +66,72 @@ the following pins to connect your SCD4x:
 Troubleshooting
 ---------------
 
+### Building driver failed
+
+If the execution of `make` in the compilation step 3 fails with something like
+
+> -bash: make: command not found
+
+your RaspberryPi likely does not have the build tools installed. Proceed as follows:
+
+```
+$ sudo apt-get update
+$ sudo apt-get upgrade
+$ sudo apt-get install build-essential
+```
+
 ### Initialization failed
 
+If you run `./scd4x_i2c_example_usage` but do not get sensor readings but
+something like this instead
+
+```
+Error executing scd4x_get_serial_number(): -1
+Error executing scd4x_start_periodic_measurement(): -1
+Error executing scd4x_read_measurement(): -1
+```
+
+then go through the below troubleshooting steps.
+
 -   Ensure that you connected the sensor correctly: All cables are fully
     plugged in and connected to the correct pin.
 -   Ensure that I2C is enabled on the Raspberry Pi. For this redo the steps on
     "Enable the I2C interface in the raspi-config" in the guide above.
--   Ensure that your user account has read and write access to the I2C device.
-    If it only works with user root (`sudo ./scd4x_i2c_example_usage`), it's
-    typically due to wrong permission settings.
+-   If running the same command as root with `sudo ./scd4x_i2c_example_usage`
+    works then your user is likely missing access permissions for the I2C 
+    interface. See the next chapter how to solve this.
+    
+### Missing I2C permissions
+
+If your user is missing access to the I2C interface you should first verfiy
+the user belongs to the `i2c` group.
+
+```
+$ groups
+users input some other groups etc
+```
+If `i2c` is missing in the list add the user and restart the Raspberry Pi.
+
+```
+$ sudo adduser your-user i2c
+Adding user `your-user' to group `i2c' ...
+Adding user your-user to group i2c
+Done.
+$ sudo reboot
+```
+
+If that did not help you can make globally accessible hardware interfaces
+with a udev rule. Only do this if everything else failed and you are 
+reasoably confident you are the only one having access to your Pi.
+
+Go into the `/etc/udev/rules.d` folder and add a new file named 
+`local.rules`.
+```
+$ cd /etc/udev/rules.d/
+$ sudo touch local.rules
+```
+Then add a single line `ACTION=="add", KERNEL=="i2c-[0-1]*", MODE="0666"` 
+to the file with your favorite editor.
+```
+$ sudo vi local.rules
+```