Extensions for the Raspberry Pi

Let There Be Light

The Raspberry Pi is supposed to be getting an official touchscreen before too long. The user will simply plug the touchscreen into the Rasp Pi board, thereby transforming the nanocomputer into a type of tablet PC [5]. Because of the increased height of the tandem setup the Raspberry Pi Foundation foresees application of the touchscreen primarily in embedded systems. The screen is supposed to have a resolution of 640x480 pixels.

The C-Berry screen from Admatec is a TFT display screen (Figure 2) that has been available for purchase for some time [6]. It costs around $45 and is connected via the SPI port. However, the display has limited resolution of about 320x240 and does not understand touch gestures. It does have the advantage of not needing an additional power supply.

Figure 2: The C-Berry display does not consume much power, but it delivers only limited resolution. ©Admatec

The Unicorn Hat [7] mini light display has 64 RGB LEDs set up in an 8x8 matrix. Each of the RGB LEDs can be controlled individually, allowing the Rasp Pi to display simple images, generate special lighting effects, or project a particular mood in a room. The manufacturer has issued a warning regarding the brightness of the LEDs. It is recommended that users avoid looking directly at the Unicorn Hat when the lights are turned on because of their extreme brightness. Users are also advised to use a diffuser to scatter or dim the light whenever possible.

The Unicorn Hat uses Pulse Width Modulation (PWM) hardware and GPIO pin 18. The Raspberry Pi should also be connected to a power supply that delivers 2A. The Unicorn Hat costs £24/$36.

Measure, Control, Regulate

Gertboard [8] is an extension that any user wanting to use the Raspberry Pi for measurements, control, or regulation should take a look at. Among other things, the board can be used as a control for motors, analog-to-digital (AD) and DA transformers, a freely programmable ATmega microcontroller, a pressure switch, and open collector outputs. The Gertboard can be connected directly to the GPIO pins with a flat ribbon cable. You can purchase one of these boards for about EUR50/$56.

The RasPiComm can be used to retrofit a series RS232 interface [9]. This adapter board gets plugged into the GPIO pins, and it offers I2C connections for things like sensors. It also offers a five-way joystick connection and an RS485 interface for attaching the control for stepper motors. The RasPiComm contains a real-time clock that runs on battery, even when the Rasp Pi is shut down; it costs $56. For the user who only needs an RS232 interface, the RS232 GPIO shield from LinkSprite is a good alternative with its $22 price tag [10]. See the "Everything at Once" box for more information.

The PiFace Clock is a battery-buffered real-time clock that costs about $10 [11]. The PiFace company also offers an extension that has two relays, four buttons, eight LEDs, eight digital inputs, and eight open collector outputs. This board costs around $25  [12].