Reading the status of more than one digital input such as a button with only one input pin is a common method of minimising I/O usage and is accomplished with a resistor network and a single analogue-to-digital pin. However as the Raspberry Pi doesn't have an ADC, another method is required.
One example of this has bee demonstrated by Instructables member JRV31 whose solution still uses a resistor network, but instead uses the resulting voltage to charge a capacitor at a varying rate depending on which button has been pressed. The Pi then monitors the duration between state changes of the digital pin connected to the circuit - and then with the timing knowledge can determine which button has been pressed.
An ingenious solution to a common problem, of which you can learn more about from the Instructable page. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
Another neat way to interface your Raspberry Pi with external hardware is to use an Arduino-compatible board - and one neat example is the Freetronics PiLeven board:
The PiLeven is an Arduino-compatible board based on the Arduino Uno, but with a few changes. Obviously it's a bit of a strange shape! The PiLeven fits right on top of a Raspberry Pi (either model B or B+) using the Raspberry Pi expansion headers.
The PiLeven also has a high-current switchmode power supply, so you can plug in anything from 7V to 18Vdc using the standard 2.1mm jack. The PiLeven can power the Raspberry Pi, so you don't need a regulated 5V USB connection anymore.
Serial communications on the PiLeven is linked through to the Raspberry Pi, so your Pi can upload new sketches straight to the PiLeven or send/receive data and commands. We've included level shifters so the 3.3V Pi can talk safely to the 5V PiLeven. And you can plug standard Arduino shields right into the PiLeven, giving your Raspberry Pi access to the huge range of shields already available. For more information about the PiLeven, including our tutorials - and to order yours today, visit the PiLeven webpage.