lcd touch screen digitizer replacement use raspberry pi made in china

Raspberry Pi OS provides touchscreen drivers with support for ten-finger touch and an on-screen keyboard, giving you full functionality without the need to connect a keyboard or mouse.

The 800 x 480 display connects to Raspberry Pi via an adapter board that handles power and signal conversion. Only two connections to your Raspberry Pi are required: power from the GPIO port, and a ribbon cable that connects to the DSI port on all Raspberry Pi computers except for the Raspberry Pi Zero line.

A number of people have used a Motorola Atrix Lapdock to add a screen and keyboard with trackpad to RasPi, in essence building a RasPi-based laptop computer. Lapdock is a very clever idea: you plug your Atrix smart phone into Lapdock and it gives you an 11.6" 1366 x 768 HDMI monitor with speakers, a keyboard with trackpad, two USB ports, and a large enough battery for roughly 5 hours of use. The smart phone acts as a motherboard with "good enough" performance. The advantage over a separate laptop or desktop computer is that you have one computing device so you don"t need to transfer files between your phone and your desk/laptop.

Unfortunately for Motorola, Lapdock was not successful (probably because of its US$500 list price) and Motorola discontinued it and sold remaining stock at deep discounts, with many units selling for US$50-100. This makes it a very attractive way to add a modest size HDMI screen to RasPi, with a keyboard/trackpad and rechargeable battery power thrown in for free.

Lapdock has two connectors that plug into an Atrix phone: a Micro HDMI D plug for carrying video and sound, and a Micro USB plug for charging the phone and connecting to the Lapdock"s internal USB hub, which talks to the Lapdock keyboard, trackpad, and two USB ports. With suitable cables and adapters, these two plugs can be connected to RasPi"s full-size HDMI connector and one of RasPi"s full-size USB A ports.

The RasPi forum has a long thread on Lapdock with many useful suggestions, photos, and links: I made a Raspberry PI Laptop. There"s also a good "blog entry at element14 with photos and suggestions of where to get cables and adapters: Raspberry Pi Laptop. TechRepublic has a tear-down article with photos of Lapdock internal components here: Cracking Open the Motorola Droid Bionic Lapdock. Paul Mano has a wealth of photos of Lapdock innards at Motorola Atrix Lapdock mod projects.

Lapdock uses the HDMI plug to tell if a phone is plugged in by seeing if the HDMI DDC/CEC ground pin is pulled low. If it"s not, Lapdock is powered off. As soon as you plug in a phone or RasPi, all the grounds short together and Lapdock powers itself on. However, it only does this if the HDMI cable actually connects the DDC/CEC ground line. Many cheap HDMI cables do not include the individual ground lines, and rely on a foil shield connected to the outer shells on both ends. Such a cable will not work with an unmodified Lapdock. There is a detailed "blog entry on the subject at element14: Raspberry Pi Lapdock HDMI cable work-around. The "blog describes a side-benefit of this feature: you can add a small power switch to Lapdock so you can leave RasPi attached all the time without draining the battery.

The Lapdock Micro USB plug is the upstream port of Lapdock"s internal USB hub, and connects to one of RasPi"s full-size USB ports. Lapdock is not USB compliant since it provides upstream power on its Vbus pin. Lapdock uses this to charge the Atrix phone. You can use this feature to power RasPi if you have a newer RasPi. The original RasPi rev 1 has 140 mA polyfuses F1 and F2 to protect the USB ports, which are too small for powering RasPi using upstream power. Newer RasPis replace F1 and F2 with zero Ohm jumpers or eliminate them entirely, which allows Lapdock to provide power. If you don"t mind modifying your original RasPi, you can add shorting jumpers over F1 and F2 or replace them with higher-current fuses.

What gets powered on depends on whether Lapdock is open or closed. If it"s open, the screen and all Lapdock USB ports are powered. If you close Lapdock, the screen and full-size USB ports are powered down, but the Micro USB still provides upstream power. This is for charging an Atrix phone. When you open or close Lapdock, the Micro USB power switches off for about a second so if your RasPi is connected it will reboot and you may have a corrupted file system. There"s discussion about this at the RasPi forum link, and someone has used a supercapacitor to work around the problem: Raspberry Pi lapdock tricks.

When you do not connect a HDMI monitor, the GPU in the PI will simply rescale (http://en.wikipedia.org/wiki/Image_scaling) anything that would have appeared on the HDMI screen to a resolution suitable for the TV standard chosen, (PAL or NTSC) and outputs it as a composite video signal.

The Broadcom BCM2835 only provides HDMI output and composite output. RGB and other signals needed by RGB, S-VIDEO or VGA connectors are however not provided, and the R-PI also isn"t designed to power an unpowered converter box.

Note that any conversion hardware that converts HDMI/DVI-D signals to VGA (or DVI-A) signals may come with either an external PSU, or expects power can be drawn from the HDMI port. In the latter case the device may initially appear to work, but there will be a problem, as the HDMI specs only provide in a maximum of 50mA (@ 5 Volt) from the HDMI port, but all of these adapters try to draw much more, up-to 500mA, in case of the R-PI there is a limit of 200mA that can be drawn safely, as 200mA is the limit for the BAT54 diode (D1) on the board. Any HDMI to VGA adapter without external PSU might work for a time, but then burn out D1, therefore Do not use HDMI converters powered by the HDMI port!

The solution is to either only use externally powered converters, or to replace D1 with a sturdier version, such as the PMEG2010AET, and to replace the power input fuse F3 with a higher rated one, as the current one is only 700mA, and the adapter may use 400mA itself. Also notice that the R-PI"s power supply also must be able to deliver the extra current.

Alternatively, it may be possible to design an expansion board that plugs into the LCD headers on the R.Pi. Here is something similar for Beagleboard:

The SOC (system on a chip) does not support any kind of analog component video, including VGA, since the SOC is designed for mobile phone use where this would not be a requirement. Additional components would be needed to generate RGB signals. Additional components would push the price beyond the $25 target and therefore won"t happen.

An additional binary blob might be required for the DSI port to function correctly (or function at all). When or if such a blob will be made available is unknown. Update 04 Jun 2013: "DSI will get done though - there are 1.5M boards out there with the connector on - that would, as you say, have been a waste of money ($120k??) if it never gets used." [1]

The schematics for apples iPhone 3gs and 4g suggest they speak DSI, thus they can probably be connected directly. The older iPhones use a "Mobile Pixel Link" connection from National Semiconductor. The 3GS panel (480×320) goes as low as US $14.88, while the 4G one (960×640, possibly the LG LH350WS1-SD01, with specifications) can be had for US $17.99 or as low as US $14.28. The connectors used might be an issue, but this connector might fit. Additional circuitry might be necessary to provide the display with required 1.8V and 5.7V for operation, and an even higher voltage for the backlight.

The Raspberry Pi provides one clock lane and two data lanes on the S2 connector, as can be read from the schematics. It is currently unknown whether this is enough to drive the iPhone 4G screen, as that screen seems be driven with three data lanes in its original application.

I2C/SPI ADC can be used to interface 4 pin resistive Touch Screens, For example STMPE812A. Texas Instruments has a solution for 4 or 8 wire touchscreens using their rather cheap MSP4309.

These have controllers and interfaces for feeding in text (and symbols). Common screen sizes include 16x2 to 40x4. They"re often seen in keypads, industrial machines, cash registers, laser printers etc.

Parallel interface displays can be found in many sizes, usually up to 7" and more. Parallel interfaces are usually 8 or 16-bits wide (sometimes 18 or 24-bit wide), plus some control-lines. The Raspberry Pi P1-connector does not contain enough GPIOs for 16-bit wide parallel displays, but this could be solved by borrowing some GPIOs from the CSI-connector or from P5 (on newer Raspberry Pis). Alternatively, some additional electronics (e.g. shift-registers or a CPLD) can be used, which could also improve the framerate or lower the CPU-load.

AdvaBoard RPi1: Raspberry Pi multifunction extension board, incl. an interface and software for 3.2"/5"/7" 16-bit parallel TFT-displays incl. touchscreen with up to 50 frames/s (3.2", 320x240)

Texy"s 2.8" TFT + Touch Shield Board: HY28A-LCDB display with 320 x 240 resolution @ 10 ~ 20fps, 65536 colors, assembled and tested £24 plus postage, mounts on GPIO pins nicely matching Pi board size, or via ribbon cable