Monthly Archives: February 2013

Reverse engineering Macbook Air FaceTime camera, part 1

A severely cracked 13″ Macbook Air display came my way some time back. The LCD panel was obviously damaged, but it would be interesting to see what makes such a great display tick, and maybe parts of it could still be used? I believe the display came from a Late 2010 Macbook Air (which would indicate an A1369 type construction), but can’t be sure. Anyway – ideas included

  • Keeping the back lighting (assuming it works) and camera, mounting the whole display on a flexible arm next to the work bench. Given the high intensity of the back lighting, it could then (maybe) provide ambient lighting AND video recording of whatever was being worked on. Maybe with a LED light and camera on a separate flexible arms.
  • If the LED backlighting drivers were toast, there should still be some nice white LEDs in there for scavenging.
  • Same thing for the camera, I believe it to be a 640×480 pixel device, nothing too exiting but could still be useful.

Turns out it’s not entirely easy to disassemble these displays. They are sealed together with very strong tape. Heating the bezel helps a lot, but it’s still a fair amount of work – and given the delicate components beneath the bezel, you might want to think twice before doing this on a laptop you care about.. Some good instructions found here, btw. Results so far:

2013-02-19_10-41-22_smallPrying the bezel open…

…before applying heat with a hot-air SMD rework station (regular heat gun would probably also work, if you are careful):
2013-02-19_10-44-38_small

Voila! Bezel is free:
2013-02-19_10-56-14_small

Now the tricky part. The cable from the cable is a thin wire with some kind of textile cover, for strengths I assume. It goes through the hinges and there is no way (as far as I can tell) to get the cable through there, without cutting off the (very small) connector that normally connects to the computers Left I/O (a.k.a. LIO) board. Cut.

Now the whole camera assembly can be removed. It also includes the ambient light sensor, which communicates over I2C. Unknown protocol for that one though – one for the future to investigate..

2013-02-23_22-55-38_small
Very tiny 6-pin connector, normally going to the LIO board.
2013-02-19_13-11-34_smallCamera module exposed in the top part of the screen. Held in place with 2 small screws.


2013-02-23_22-32-08_smallCamera board. 

2013-02-19_13-17-59_smallThese things are small – fingers included for scale reference.

With six wires in the cable it’s pretty clear that 4 are for USB (+5V, Gnd, Data+, Data-) and 2 for I2C. That cable is however crazy small – it’s about 2 mm diameter. Once the outer layer is off, you see 6 even thinner cables. 2 are black, 4 transparent. Which ones are which?

Google is your friend. Turns out there are schematics to be found if you Google long enough. Turns out you need schematics for the LIO board though, in order to get the pinout of the camera/ALS cable, and it’s nowhere to be found for the A1369. Did find a schematic for the A1370 model though (same computer but 11″ screen), with a bit of luck that cable is the same between models.

The 2 black ones are prime candidates for +5V and Gnd. Cutting away the insulation revealed that the cables are shielded, with a center wire that is barely visible to the eye. It took several attempts before I had separated the wires from the sheilding, and then done the same with the other 4 wires. Soldering these onto an old USB cable was then easy (but ugly!!):

2013-02-28_14-09-48_small

Still, it doesn’t work. The camera is not recognised on an iMac with latest OSX, nor on a Windows 8 laptop. Happened to have a Raspberry Pi lying on the work bench, tried it too with same result: nothing.

But wait… doing a “tail -f /var/log/messages” on the RPi showed that it DID recognise the camera, but that the camera wanted more power than a non-powered USB hub could provide! Placing the camera into the RPi’s regular USB port made it appear nicely when doing a “lsusb” command.

Still, it didn’t work when I connected the camera to the Windows or iMac machines – strange.

Also, the RPi loose contact with the camera after a while – no idea why. Could maybe be a bad USB cable (it’s from an old mouse using USB 1.1 – maybe that’s a problem??), or is there too much noise introduced by the ugly splicing of cables that I’ve done? No idea… More investigation needed. Anyway, the camera enumerates with USB id 05ac:850a, which indeed is an Apple FaceTime camera – nice!

Smoke tester from Dangerous Prototypes

A while back I got a free PCB from Dangerous Prototype’s Free PCB program. It’s a nice little board designed to provide easy current monitoring during prototype stages of a project. Features include over-current tripping with visual indication, as well as dual 5V and 3.3V supplies.

So, a week or two ago I was about to reverse engineer a laptop camera (built with very small components…). The camera’s attaching cable has unknown pinout, but system block diagram indicate it’s a USB 2.0 device. The cable is a 6-wire variant, so it shouldn’t be too hard figuring out which wire does what. It would however be nice to have a controlled power source feeding the camera during the work.

Enter the smoke tester… I figured I would build it, to the extent possible, with parts already found in the lab, if needed maybe even scavenging some old computer or similar..

The result is pretty nice:

smoke_tester_20130227

Some comments/feedback on the design:

  • Input power screw terminals don’t have +/- marked on the board.
  • Holes for bana jacks too small for any of the jacks I’ve tried.
  • Really nice with the three parallel pads for INA 138 load resistors. They give good flexibility for selecting shunt resistors for the INA 138. For example, I used a 0.1 ohm (instead of 0.075 ohm as suggested in the schematic) shunt resistor, which means the load resistor should be 50 kohm. Easy – two 100 kohm resistors in parallel does the trick.
  • Documentation is very limited, basically just a forum thread and schematics (that don’t include all component values, e.g. R13 and R14.

A few components are missing on thew board:

  • USB out connector. I had a hard time finding an SMD connector that would work. Figured I’d mainly be using the screw terminals anyway.
  • Banana jacks. Going through the parts bins here, all the banana jacks were too big to fit in the PCB’s holes. Those wholes could be a bit larger, IMHO.
  • Input power jack. Couldn’t find a suitable SMD one, but as I will be taking power from a wall wart with USB output I will be fine.
  • R13, R14. There is no value for these in the schematics (as far as I can tell), leaving them out thus. But as the USB out connector is unpopulated anyway, it’s not a problem (right now). Edit: They should be ca 20 ohms.

Links:
Dangerous Prototype’s forum page