RaspberryPi - GPIO control over Web Interface

How to use RaspberryPi inputs and outputs? The easiest way is to use the GPIO pins directly on the RaspberryPi board.

Hardware

Raspberry Pi has 8 freely accessible GPIO ports. which can be controlled. In the following picture they are colored green. 

GPIO ports

Attention!!! GPIO are 3.3V and do not tolerate 5V !! Maximum current is 16mA !! It would be possible to use more of them by changing the configuration.

Software

First you need to install the ligthhttpd (or apache ) server and PHP5:
sudo groupadd www-data
sudo apt-get install lighttpd
sudo apt-get install php5-cgi
sudo lighty-enable-mod fastcgi
sudo adduser pi www-data
sudo chown -R www-data:www-data /var/www
In the lighthttpd configuration

you need to add:
bin-path" => "/usr/bin/php5-cgi
socket" => "/tmp/php.socket"

Now you need to restart lighthttpd:
sudo /etc/init.d/lighttpd force-reload

This will run our webserver with PHP.

Now we get to the actual GPIO control. The ports can be used as input and output. Everything needs to be done as root.

First you need to make the port accessible:
echo "17" > /sys/class/gpio/export

Then we set whether it is an input (in) or output (out):
echo "out" > /sys/class/gpio/gpio17/direction

Set the value like this:
echo 1 > /sys/class/gpio/gpio17/valu

Read the status:
cat /sys/class/gpio/gpio17/value

This way we can control GPIO directly from the command line. If we use the www interface for control, we need to set the rights for all ports so that they can be controlled by a user other than root.
chmod 666 /sys/class/gpio/gpio17/value
chmod 666 /sys/class/gpio/gpio17/direction