A portable single board computer such as the Raspberry Pi or the RBPi ought to have a portable screen, preferably a touch screen that is comfortable to use. This is a long overdue, much sought-after request from users, especially from developers, who see and use several smartphones and tablets with capacitive and or resistive touch screens.
The Pi Foundation has been hard at work on developing a seven-inch touch screen as an add-on to the RBPi. This would be appropriate for a number of projects where you would want to pit the RBPi against a portable tablet or even a laptop. However, for development of embedded systems, people prefer a smaller and more compact version of display. The 2.4-inch TouchScreen display from 4D Systems fills this void perfectly and affordably, being compatible with the RBPi models A+, B+ and RBPi2.
The TouchScreen is almost as large as the RBPi board and covers it as far as the USB and Internet ports, while sitting perfectly on the bank of GPIO pins and covering all of them. At present, the other end of the TouchScreen hangs as there is no support and there is a possibility of its backside touching the connectors. You can expect a set of stand-offs to come soon and these will secure the screen above the connectors and pins of the RBPi.
According to an intentional design decision between 4D Systems and element14, the TouchScreen fits very neatly within the official case of the RBPi. That leaves out only the portable power, which, if the official case could support, would have made the RBPi truly portable.
The 30 gm. TouchScreen module dimensions measure 56.5×65.0x14.2 mm. It has a viewing area of 49.0×36.7 mm, with four mounting holes of 2.6 mm diameter. The QVGA TFT screen has a resolution of 240×320 pixels and sports 65K true to life colors. Integrated with the screen is a 4-wire resistive touch panel. You can display the full GUI output or the primary output on the TouchScreen, just as would a monitor connected to the RBPi. The display uses a PWM control for the backlight and on board, there are three backlight choices, selectable with jumpers – On, Off and PWM.
The display module connects to the RBPi via a high-speed SPI interface working at 46MHz and using SPI compression technology. If you have a kernel that compresses images, expect higher frame rates than the typical value of 17 frames per second. The module does not require a separate power supply as it powers itself directly from the RBPi.
Although the screen has full capabilities, its limitations are because of the way Linux handles framebuffers. For example, although the display can play full motion video, you cannot render OpenGL to the screen. That means you cannot expect hardware acceleration from the SPI screen. Someday, this may be possible if someone tweaks the Broadcom code for the VideoCore and OpenGL.
