Display
The first-generation OLPC laptops have a novel low-cost liquid crystal display (LCD). It has a 1200 × 900 7.5 inch (19 cm) diagonal transflective LCD (200 dpi) that uses 0.1 to 1.0 W depending on mode. There are two modes: Reflective (backlight off) monochrome mode for low-power use in sunlight. This mode provides very sharp images for high-quality text and Backlit color mode, with an alternance of red, green and blue pixels. The XO 1.75 developmental version for XO-3 has an optional touch screen.
The electronic visual display is the costliest component in most laptops. In April 2005, Negroponte hired Mary Lou Jepsen, who was interviewing to join the Media Arts and Sciences faculty at the MIT Media Lab in September 2008, as OLPC Chief Technology Officer. Jepsen developed a new display for the first-generation OLPC laptop, inspired by the design of small LCDs used in portable DVD players, which she estimated would cost about $35. In the OLPC XO-1, the screen is estimated to be the second most costly component, after the central processing unit (CPU) and chipset.
Jepsen has described the removal of the filters that color the RGB subpixels as the critical design innovation in the new LCD. Instead of using subtractive color filters, the display uses a plastic diffraction grating and lenses on the rear of the LCD to illuminate each pixel. This grating pattern is stamped using the same technology used to make DVDs. The grating splits the light from the white backlight into a spectrum. The red, green, and blue components are diffracted into the correct positions to illuminate the corresponding pixel with R, G or B. This innovation results in a much brighter display for a given amount of backlight illumination: while the color filters in a regular display typically absorb 85% of the light that hits them, this display absorbs little of that light. Most LCD screens at the time used cold cathode fluorescent lamp backlights which were fragile, difficult or impossible to repair, required a high voltage power supply, were relatively power-hungry, and accounted for 50% of the screens' cost (sometimes 60%). The light-emitting diode (LED) backlight in the XO-1 is easily replaceable, rugged, and low-cost.
The remainder of the LCD uses extant display technology and can be made using extant manufacturing equipment. Even the masks can be made using combinations of extant materials and processes.
When lit primarily from the rear with the white LED backlight, the display shows a color image composed of both RGB and grayscale information. When lit primarily from the front by ambient light, for example from the sun, the display shows a monochromatic (black and white) image composed of just the grayscale information.
"Mode" change occurs by varying the relative amounts backlight and ambient light. With more backlight, a higher chrominance is available and a color image display is seen. As ambient light levels, such as sunlight, exceed the backlight, a grayscale display is seen; this can be useful when reading e-books for an extended time in bright light such as sunlight. The backlight brightness can also be adjusted to vary the level of color seen in the display and to conserve battery power.
In color mode (when lit primarily from the rear), the display does not use the common RGB pixel geometry for liquid crystal computer displays, in which each pixel contains three tall thin rectangles of the primary colors. Instead, the XO-1 display provides one color for each pixel. The colors align along diagonals that run from upper-right to lower left (see diagram on the right). To reduce the color artifacts caused by this pixel geometry, the color component of the image is blurred by the display controller as the image is sent to the screen. Despite the color blurring, the display still has high resolution for its physical size; normal displays as of February 2007 put about 588(H) × 441(V) to 882(H) × 662(V) pixels in this amount of physical area and support subpixel rendering for slightly higher perceived resolution. A Philips Research study measured the XO-1 display's perceived color resolution as effectively 984(H) × 738(V). A conventional liquid crystal display with the same number of green pixels (green carries most brightness or luminance information for human eyes) as the OLPC XO-1 would be 693 × 520. Unlike a standard RGB LCD, resolution of the XO-1 display varies with angle. Resolution is greatest from upper-right to lower left, and lowest from upper-left to lower-right. Images which approach or exceed this resolution will lose detail and gain color artifacts. The display gains resolution when in bright light; this comes at the expense of color (as the backlight is overpowered) and color resolution can never reach the full 200 dpi sharpness of grayscale mode because of the blur which is applied to images in color mode.
Power
The laptop design specification goals are about 2 W of power consumed during normal use, far less than the 10 W to 45 W of conventional laptops. With build 656, power use is between 5 and 8 watts measured on G1G1 laptop. Future software builds are expected to meet the 2-watt target.
In e-book mode (XO 1.5), all hardware sub-systems except the monochrome dual-touch display are powered down. When the user moves to a different page, the other systems wake up, render the new page on the display, and then go back to sleep. Power use in this e-book mode is estimated to be 0.3 to 0.8 W. The XO 2.0 is planned to consume even less power than earlier versions, less than 1.0 W in full color mode.
Power options include batteries, solar power panels, and human-powered generators, which make the XO self-powered equipment. 10 batteries at once can be charged from the school building power in the XO multi-battery charger. The low power use, combined with these power options are useful in many countries that lack a power infrastructure.
- DC input, ±11–18 V, maximum 15 W power draw
- 5-cell rechargeable NiMH battery pack, 3000 mAh minimum 3050 mAh typical 80% usable, charge at 0...45 °C (deprecated in 2009)
- 2-cell rechargeable LiFePO4 battery pack, 2800 mAh minimum 2900 mAh typical 100% usable, charge at 0...60 °C
- Four-cell rechargeable LiFePO4 battery pack, 3100 mAh minimum 3150 mAh typical 100% usable, charge at −10...50 °C
Networking
IEEE 802.11b support will be provided using a Wi-Fi "Extended Range" chip set. Jepsen has said the wireless chip set will be run at a low bit rate, 2 Mbit/s maximum rather than the usual higher speed 5.5 Mbit/s or 11 Mbit/s to minimize power use. The conventional IEEE 802.11b system only handles traffic within a local cloud of wireless devices in a manner similar to an Ethernet network. Each node transmits and receives its own data, but it does not route packets between two nodes that cannot communicate directly. The OLPC laptop will use IEEE 802.11s to form the wireless mesh network.
Whenever the laptop is powered on it can participate in a mobile ad hoc network (MANET) with each node operating in a peer-to-peer fashion with other laptops it can hear, forwarding packets across the cloud. If a computer in the cloud has access to the Internet—either directly or indirectly—then all computers in the cloud are able to share that access. The data rate across this network will not be high; however, similar networks, such as the store and forward Motoman project have supported email services to 1000 schoolchildren in Cambodia, according to Negroponte. The data rate should be sufficient for asynchronous network applications (such as email) to communicate outside the cloud; interactive uses, such as web browsing, or high-bandwidth applications, such as video streaming should be possible inside the cloud. The IP assignment for the meshed network is intended to be automatically configured, so no server administrator or an administration of IP addresses is needed.
Building a MANET is still untested under the OLPC's current configuration and hardware environment. Although one goal of the laptop is that all of its software be open source, the source code for this
Shell
Yves Behar is the chief designer of the present XO shell. The shell of the laptop is resistant to dirt and moisture, and is constructed with 2 mm thick plastic (50% thicker than typical laptops). It contains a pivoting, reversible display, movable rubber Wi-Fi antennas, and a sealed rubber-membrane keyboard.
More than twenty different keyboards have been laid out, to suit local needs to match the standard keyboard for the country in which a laptop is intended. Around half of these have been manufactured for prototype machines. There are parts of the world which do not have a standard keyboard representing their language. As Negroponte states this is "because there's no real commercial interest in making a keyboard". One example of where the OLPC has bridged this gap is in creating an Amharic keyboard for Ethiopia. For several languages, the keyboard is the first ever created for that language.[2]
Negroponte has demanded that the keyboard not contain a caps lock key, which frees up keyboard space for new keys such as a future "view source" key.
Beneath the keyboard was a large area that resembled a very wide touchpad. The capacitive portion of the mousepad was an Alps GlidePoint touchpad, which was in the central third of the sensor and could be used with a finger. The full width was a resistive sensor which, though never supported by software, was intended to be used with a stylus. This unusual feature was eliminated in the CL1A hardware revision because it suffered from erratic pointer motion. Alps Electronics provided both the capacitive and resistive components of the mousepad.
- Water-resistant membrane keyboard, customized to the locale in which it will be distributed. The multiplication and division symbols are included. The keyboard is designed for the small hands of children.
Release history
The first XO prototype, displayed in 2005, had a built-in hand-crank generator for charging the battery. The XO-1 beta, released in early 2007, used a separate hand-crank generator.
The XO-1 was released in late 2007.
The XO 1.5 was released in early 2010.
The XO 1.75 began development in 2010, with full production starting in February 2012.[3]
The XO 2, previously scheduled for release in 2010, was canceled in favor of XO 3. With a price target US$75, it had an elegant, lighter, folding dual touch-screen design. The hardware would have been open-source and sold by various manufacturers. A choice of operating system (Windows XP or Linux) was intended outside the United States. Its US$150 price target in the United States includes two computers, one donated.
The OLPC XO-3 was scheduled for release in late 2012. It was canceled in favor of the XO-4. It featured one solid color multi-touch screen design, and a solar panel in the cover or carrying case.
The XO 4 is a refresh of the XO 1 to 1.75 with a later ARM CPU and an optional touch screen. This model will not be available for consumer sales. There is a mini HDMI port to allow connecting to a display.
The XO Tablet was designed by third-party Vivitar, rather than OLPC, and based on the Android platform whereas all previous XO models were based on Sugar running on top of Fedora.
