External Display from an iPad LCD, Part 2

Last post I showed how all the electronics stuff would work for the iPad screen.  After getting screen working it took me a few months to actually sit down and assemble everything.  Once I got around to it, it just took one evening to physically put everything together.

I first laser cut a bezel for the screen out of some thick black acrylic.  I then milled out a recess for the screen in the acrylic bezel.  I fixed the acrylic to the mill using this fancy milling fixture I machined a while back.

Rather than trying to desolder the Displayport jack from the LCD controller, I instead just cut and spliced a Displayport cable down to 8".  Same with the USB 3 cable.  Tip:  Splicing Displayport cables is terrible.  There's an absurd amount of shielding, along with the ~20 conductors you have to deal with.  Avoid if possible.

The thickest part of the entire assembly is connectors.  If this project was redone without internal connectors and with custom lower-profile electronics, it could easily be built to iPad-thickness.

For the back panel, I used the side panel of a PowerMac G5 case.  The 1/8" thick aluminum sheet is absolute overkill for this application, but I couldn't resist the anodized apple on the back.  A more reasonable material may be the back of a broken macbook screen, which would be much thinner and lighter.

I briefly considered just gluing the entire assembly together (it would have been a very Apple thing to do)  but then came to my senses and drilled and tapped some holes to screw it together.  Eventually I'll get some flat cap screws and countersink them.

To turn the Mini Displayport and USB connector into one piece, I 3D-printed a housing the two connectors press-fit into, at the appropriate spacing for my laptop's ports:

To attach the LCD to my laptop's built-in screen, I also went to my 3D printer and made these clips that friction-fit over my laptop's bezel.  This way the LCD just presses onto the side of my laptop screen, and can be removed and installed in a matter of seconds.  These printed clips were glued to the side of the acrylic bezel.

The assembly installed on my laptop:

External Display from an iPad LCD, Part 1

Last summer, Bayley, Sherry and I got a stack of iPad 3 LCD off ebay for $50 apiece.  These are 2048x1536 9.7" LCDs, and a cool thing about them is that they use a displayport interface internally.  This means you can splice the ribbon connector that comes with an LCD into a normal display port cable, add a backlight driver, and use the display with any computer.  This is a fairly straight forward and well documented.

My original plan was to build my own board and backlight driver.  After sitting on the LCD for over 6 months without making any progress, I decided to just get a premade breakout board and backlight driver from here for around $35.

This particular board has built in LED drivers for the backlight as well as adjustable brightness and USB power.  Unfortunately, at full brightness the assembly draws over an amp at 5V, meaning it can't be directly powered off USB.  Here's the board with the LCD working, powered off the bench supply:

When powered only off the USB port, half of the backlight turns off or flickers:

 Fortunately, the controller built into the board lets you adjust the backlight brightness.  I lowered the brightness to a level where brightness was still reasonable, but current draw dropped to around 600 mA.

I then looked up the datasheet for the backlight driver.  Here it is.  According to the datasheet, the current limit is set by a resistor according to a formula on page 11.  I found some appropriate SMD resistors for a current limit of 600 mA at MITERS, and replaced the stock resistors that came with the board.

Swapped resistors circled in red

This lowered the default brightness, and made current draw a bit more reasonable.  But 600 mA is still too much for a USB 2 device (which the board is), which is capped at 500 mA.  However USB 3, which my laptop has, can supply up to 900 mA to devices that identify to the computer as high power USB 3 devices.

To trick my computer into making the full USB 3 current available, I ran to Microcenter and bought the cheapest ($10) external USB 3 hard drive enclosure I could find.  I assumed that since it was listed as being able to power spinning HDD's (not just SSDs) just off the USB port, it would probably be a high power device.

Plugging it in and checking the device properties confirmed this, so I stripped the enclosure apart.  The electronics fortunately were extremely compact:

To leach power off the board, I just added jumpers between the LCD driver board and the power pins on the enclosure board.  

Yes, my LCD has a SATA port in it...

Here's the screen running only of a mini displayport and a USB port:

Building an enclosure will be wrapped up in part 2.