To most people, the Raspberry Pi or the RBPi Single Board Computer is only a cheap desktop. That is because by the time you have added a monitor, a keyboard, a mouse and the SD card, it would have cost as much as a cheap laptop and would still be a lot less powerful.
However, the real innovation of the RBPi lies not in its cost, but in its form factor. You can run the tiny RBPi on a few batteries or solar cells and use its exposed General Purpose Input and Output pins. This trio of combinations does not have any precedents in computing, at least not in the price range of the RBPi.
Being a new type of device, the RBPi is a lot easier to understand with some of the readily available components that connect to it to enable some function or to add some feature.
Most of these add-on components are not from large companies, but developed by hobbyists who saw the need for and filled it. One of these add-on components is the multi-purpose LED display Pi Lite. This is a simple board full of LEDs allowing people to use the RBPi to turn them on or off individually. This has made the RBPi SBC different from the regular PC and forced people to think differently for using it in its particular niche.
Pi Lite has 126 red LEDs, with a white LED version on its way. You plug the board into the GPIO pins on the RBPi. Pi Lite nearly covers the main RBPi board and has about the same form factor. Of course, you need a little configuration to enable the board to use the RBPi serial port, but that is well documented.
You send commands to the Pi Lite via a minicom terminal. Once connected over the serial port, anything sent over will scroll across in beautiful red light. Not only can you send text, you can also send commands preceded by three-dollar signs. You can turn all pixels on or off, display horizontal and vertical graphs and manipulate individual pixels.
You can improve the connectivity of your RBPi by expanding its ports. As the GPIO pins are exposed, any circuitry can be added to the RBPi. That may cause accidents and fry your RBPi very easily. Although there are several add-on boards that provide access and protection to the RBPI GPIOs, Quick2Wire has a board that uses the I2C and SPI features of the RBPi.
These are the Inter-Integrated Circuit and Serial Peripheral Interface and the board comes in two parts. The main board provides the I2C and SPI ports, adds protection for the RBPi and voltage selectors. Additional boards provide more GPIO ports including analog inputs and outputs that RBPi lacks. You can daisy-chain the boards to allow even more ports to be added to the RBPi.
To control the ports, you need to program the board with the Python programming language. For this, you may have to install the python3-setuptools package. You can find additional details of the above two add-on boards in openmicros.org and Quick2Wire.com.