Merge pull request #18 from Tri413/GPIO

Added GPIO 1W instructions

Author: sailoog

docs/gpio/gpio_app.md

@@ -1,3 +1,20 @@
 # GPIO
+Before starting, make sure to enable the *1-Wire* interface on the Raspberri PI Configuration app.
 
-Coming soon.
+![Interfaces](img/pi-1-wire.png)
+
+To start using GPIO sensors like 1W 18B20 temperature sensors, you will need to install the OpenPlotter GPIO app.  OpenPlotter apps are installed from the OpenPlotter -> Settings application.  Click *Refresh* to verify the installed Apps.  By default GPIO is not installed so select it and click *Install*.  After installation, you will now see the GPIO app in the OpenPlotter menu.
+
+![Screen](img/gpio.png)
+
+When you open the GPIO app, you will now see your 1-Wire sensors listed.  You will need to edit them to add the correct Signal-K key name.  The names have a specific format and the *Edit* button will assist you with creating the correct key name.  
+
+![Sensor](img/sensor-edit.png)
+
+It is important to use a valid key name so that Signal K will utilize the correct unit of measure.
+
+![Keys](img/signalk-keys.png)
+
+After you have added a Signal K key, you should see your sensor listed in the Signal K *Data Browser*.
+
+![Browser](img/signalk-data.png)