Something new and interesting.

So, my breakouts for the Macbook Pro Retina’s I-PEX display connector are finished and are on the way from the supplier.  This has been a long ten days.  But it’s not all roses, they’re set to arrive on Monday, the day I start a week of travel for work.  So there will be no fun display hacking time for the next week.  Oh well.

But in the meantime I have turned my attention to the other bundle of cables coming from the display – the antenna and camera connections.  The antennas aren’t all that interesting – we could use them, but they don’t provide a function on their own and the hardware necessary to make use of them would be more complex than it would be worth.  Plus both of my displays have the antenna wires cut.  On the other hand, the camera is a bit more useful.  And like the panel itself, it can be made operable with little more than a connector breakout.

Apple cameras (“iSight”, or more recently “FaceTime”, embedded cameras) have been USB based for a number of generations of MacBook, since at least 2006.  Similar to normal USB, the camera connector traditionally contains 5V, GND, and two USB data lines.  However in addition to this, most Apple camera connectors also carry an i2c interface.  We’ll talk about that a bit more later.

There are plenty of different Apple camera units, a unique one for each model and generation of Macbook.  Over the years they have been built in a number of different form factors, and have been terminated with several different types of connectors.  And within these connectors, the wiring has been arranged in several pinouts.  So while I have some Macbook schematics and know what to expect in general, it is not so easy as applying a “generic” pinout to this unit.

The Macbook Pro Retina display assembly’s camera connector is made by ACON (Advanced Connectek); the part number is currently unknown.  It’s a six-position connector with 0.4mm pitch, likely a solder-type part as the flat contacts appear to be integral to its body.  A bead of epoxy seals the wires into the connector.  Six individual black wires run from the connector to the camera.  The wires are somewhere in the 0.3-0.35mm diameter range, stranded, and uniquely jacketed – the black jacket appears to have a copper coating on the inside.  The wires are bound together with sticky black fabric tape and enter the display assembly on the righthand side of the bottom edge after about 150mm of free cable tail.  On the way it passes through the righthand hinge assembly.

The camera module sits behind the main display glass.  According to the iFixit teardown of the Retina display unit, the glass can’t be reliably removed without damaging it.  Therefore it would be best to figure out the pinout without having to inspect the camera board directly.  The ideal way to do this would be to pull the pinout directly from the schematic, but as I have not yet found a schematic for the A1398 Macbook Pro, we must devise another way.

One way or another, a mate connector for the camera would be desirable, to avoid having to cut the cable.  As I have been unable to find a source of these directly, I bought a Macbook Air camera mainboard sans lens.  I was very careful to inspect the myriad Macbook cameras available, because many of these – INCLUDING the A1398 camera – appear to use FFCs or other types of connectors, which will not mate with the motherboard side of the camera harness.  Here’s the board I bought:

The side advantage of having an additional camera board to fondle is the ability to probe and investigate how Apple designs their camera boards in general.  So what have we here?  First we will evaluate the silicon present on the board.  The most prevalent IC is U2, a Vimicro VC0336BSHB USB webcam interface ASIC.  From the product brief, we can see that this chip talks to a CMOS image sensor over LVDS, has a serial interface for a flash memory, has mic inputs and an AC’97 codec interface and speaks to the PC over USB.

Next to this is a SST SST39LF010 1Mbit flash memory, which is probably where configuration information such as the USB device descriptors are stored.  Next to this is a suspiciously placed chip with a pair of inductors underneath, which predictably is a dual buck regulator, a TI TPS62402DRC (marking BYH).  This IC provides a fixed (1.8 or 1.2V)/400mA and 3.3V/600mA.

That’s enough to work with.  The datasheet for the TPS62402 notes that pin 8 is GND and pin 3 is VIN.  Some probing reveals that in the input connector beginning at the left (marked with a silkscreen arrow), pin 1 is +5V and pin 6 is GND.  This is reaffirmed by the connection between GND and the metal body of the connector.  While we’re at it, EN1, EN2 and DEF_1 are pulled to +5V, meaning both supplies are permanently enabled, and the output voltages are 3.3V and 1.8V.

Conspicuously, two of the remaining pins (4 and 5) are run through a common mode ferrite bead.  This wouldn’t make sense for an i2c SCL/SDA line, since the two signals are not complements of one another and would be attenuated by the bead.  So we will guess that these are the USB connections, and the remaining two (2 and 3) must then be i2c.  Probing the i2c lines to random points on the board indicated that the lines run through the J3 board-to-board connector that connects the image sensor daughterboard.  We’ll remember that for later.

That was enough of this board.  Now, on to the real deal.  We know that the shield of the connector should be connected to GND.  If we are very lucky this will also be true on the opposite end of the cable – fortunately we are, and it is simple to confirm that pin 6 (as mated to the Air camera board) is GND as it is tied to the metal body of the connector.

Now for the 5V line.  Most power rails have some sort of capacitance to ground to smooth the line when brief current pulses are drawn from it.  In the Air board, measuring across the known power leads returns an input capacitance of 8.8uF.  Measuring any of the other leads to ground returns much smaller capacitances.  So this seems to be a reliable way to locate +5V.

We can guess that +5V should be pin 1.  But no!  Measuring the capacitance between this pin and the metal connector shell on the panel revealed a fairly insignificant capacitance.  In fact, when the rest of the pins are probed, only pin 3 exhibits a high (6.3uF) capacitance indicative of the +5V pin.  So immediately, the pinouts are different.

Knowing where the voltage rails are located is enough to work with.  If I was desperate I could use the same method for finding the rest of the pinout as I plan to use on the display connector – connect one pair at random, see if it enumerates, if not, reverse it, if it still doesn’t, swap for the other pair and repeat.  But I decided to cheat a bit and researched the Macbook schematics that I have to see if Apple had previously used a pinout with Ground, two skipped pins, then 5V.  I found the answer to this in the schematic for the Macbook Air A1370 LIO board – a pinout with GND as pin 1, 5V as pin 4, and two USB and two i2c pins:

This is very valuable information.  First of all, it notes that the pin numbering on this side of the board is different than the silkscreen on the Air board, placing GND as pin 1 instead of pin 6, etc.  Second, it makes the pinout (1-6) GND, USB_D+, USB_D-,+5V, I2C_SCL, I2C_SDA – this makes a lot of sense, as the pinout for normal USB connectors is +5/D-/D+/GND.

So without further ado, let’s see if this pinout is accurate.  I pulled the socket off of the Air board with my hot air station and wired it to a cut USB cable.

Now, when connected to the USB port, gasp!  New devices!

The camera enumerates as a USB Composite Device (USB\VID_05AC&PID_8510&REV_8025) with two sub-devices, both identified as “FaceTime HD Camera (Built-in)” (USB\VID_05AC&PID_8510&REV_8025&MI_00 and _02).  The _00 device installs automatically with generic Windows imaging device drivers; the _02 device claims no drivers could be found.  The solution is probably to dig through the BootCamp drivers and find one, but that’s a headache for another day.

So there you have it!  Camera operational, simple as that.  But what about the i2c connection?  What does it do?  The answer to that is in the schematic as well.  The netnames are “I2C_ALS_SCL” and “I2C_ALS_SDA”.  These are the communication bus for the Macbook Pro’s ambient light sensor.  I will leave the protocol hacking of the ALS for another post.

For those who wish to hack around with the camera and ALS, I have drawn up a simple breakout board with a camera connector, a mini-USB, and a 0.050″ header for the ALS.  I’ll post files for that board here as soon as I get a chance.  Remember though that I don’t have a source for the camera connector mate socket, so you’ll probably need to source a used camera board with the appropriate connector and harvest it.  The price is not bad; I paid about $6 for mine.

That’s enough for this installment.  Next time, hopefully I’ll be showing off the working panel.

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A lot of people have been asking about how much these boards cost, so it seems worthwhile to post a little something to clear this up.

I’m not looking to make a huge profit of any of this.  Actually it just makes me happy that anyone is interested at all in what I’m doing.  So rather than keep my costs under wraps and provide you with a blackbox number, here is the actual amount that it costs me to build one of these boards, by component (in USD):

Component	Vendor	Vendor PN	Cost ea	Qty	Ext Cost
PCB, MM PCB10002 REV B, Simple iPad Breakout	OSH Park	PCB10002 REV B	3.17	1	3.17
Connector, DisplayPort, SMD, Molex 0472720001	Digikey	WM19271CT-ND	5.30	1	5.30
Connector, FFC, 51 Pos, 0.3mm Pitch, Molex 5022505191	Mouser	538-502250-5191	5.56	1	5.56
Capacitor, Alum Elec, 100uF, 10V, TH, Panasonic EEUFR1A101	Digikey	P14373-ND	0.33	1	0.33
Diode, Schottky, dual common cathode, 25V, 1A, TO-261, NXP BAT120C,115	Digikey	568-6921-1-ND	0.77	1	0.77
LED, Green, SMD 0805, OSRAM LG R971-KN-1	Digikey	475-1410-1-ND	0.08	1	0.08
Resistor, 100 ohms, 1%, 1/10W, 0603, Yageo RC0603FR-07100RL	Digikey	311-100HRCT-ND	0.10	1	0.10
Resistor, 100 ohms, 1%, 1/16W, 0402, Stackpole RMCF0402FT100R	Digikey	RMCF0402FT100RCT-ND	0.025	12	0.30
Resistor, 0 ohms, 0603, Yageo RC0603JR-070RL	Digikey	311-0.0GRTR-ND	0.10	2	0.20
				Total	15.81

Now, not all of these parts are used in the same buildup.  The diode and the 0 ohm resistors aren’t installed at the same time; the 0402 resistors aren’t installed at all if the board is to be used for a projector build as they’d be unnecessary, etc.  But I will kit all the boards based on this set of parts anyway, so this is the base cost for one unit.

There are additional ancillary costs not rolled into the above BOM.  Packaging costs (antistatic bag, padded envelope), pre-soldered wires (if desired), assembly materials (solder paste, flux remover, etc), assemble-it-yourself materials (stencil, if desired).  And you’ll note that I have not touched labor yet – if you want me to build up the boards, I will need to charge a nominal assembly fee.  I won’t charge you a fortune, but it would be foolish to work for free.

I have quotes out at stencil manufacturers and will query the usual shipping suspects for pricing this week ([EDIT 2013.08.08] Shipping to the continental US is typically $3 for one or two units, shipping international is averaging about $7).  The cost is $20 for a kit of parts, $30-$35 for an assembled board (pending stencil quote [EDIT 2013.07.09] None of the inexpensive stencil fabricators can do the aperture/web sizes on this board, so I’d need a professional stainless-steel stencil – which I won’t go for unless I get enough people interested in boards to offset the cost), plus shipping to your location.  Note that this isn’t a start-to-finish kit – you’ll still need to provide a stable 3.3V source (assuming your DisplayPort cable doesn’t do so), and a source of 19-20V if you want to drive the backlight.  This board was designed for the DIY projector crowd to be as cheap and simple as possible, so please be aware of its limitations.

I hope the projected cost isn’t more than expected.  Labor is going to be the thing that really drives the price – right now it takes me an hour or so to build a board since I’m applying paste by hand.  I hope that I can get a stencil done for a reasonable price to reduce that effort.  We’ll see.  Nope.

More on this later.  If you’re interested, please drop me a comment or an email so I can gauge interest.  If a hundred people want one, a $180 professional stencil suddenly isn’t quite so big a deal (this board is too complex for the most inexpensive prototype laser services).  Plus then quantity discounts start to apply on components and the BOM cost drops.  Which means cheaper boards for all!  Yay!

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D’oh.

A shipment of components including the connectors intended for the Macbook LCD breakout board arrived yesterday.  I-PEX components are not carried at the usual US distributors, so I opted to order a TE part that a random source seemed to indicate might mate (5-2069716-2).  Well…

That’ll teach me for not doing my research.  The pin pitch isn’t even correct.  So I cost myself a few bucks and a week of time.  Damn it all.  But I have ordered a few genuine I-PEX Cabline-CA connectors on eBay, so in only another two weeks, I should have things figured out enough to spin a “proper” simple breakout.  The long leadtime of OSH Park is really killing me these days.

In the meantime, Daniel has sent me some more photos of his Samsung controller boards and has made great progress in his efforts.  The Samsung boards look like this:

His progress has compelled me to do a little additional work of my own – even though I swore I wouldn’t solder more jumpers to the panel.  Oh well, promises were meant to be broken.  In order to know where to stick wires, I have spent some time investigating the hardware that makes up the controller PCB.  The brain of the display is the ParadeTech DP635 LCD timing controller.  While the specification for this part is not freely available, ParadeTech sells several other Tcons, such as the DP628.  Here is a block diagram of the innards of that part:

We will assume that the DP635 works sorta-similar.  From this, we can deduce that this IC takes in the DisplayPort signal and spits out something compatible with the chip-on-glass driver ICs on the panel.  In the ‘628 this is miniLVDS, and it’s reasonable to guess that this may be similar to the way it is done in the ‘635.  The backside of the controller PCB has pairs of testpoints labeled D1D1P/D1D1N, D1D2P/D1D2N through D9D1P/D9D1N, D9D2P/D9D2N, nine pairs of pairs in all.  Presumably this is eighteen differential pairs carrying the decoded video data as converted from the DisplayPort source.  As my panels are functional I will leave this as a theory and not pull off the IC to probe it out to the testpoints.

Speaking of testpoints, there are plenty of them.  Here’s a list of the marked points, primarily found on the connector side of the PCB:

• D1D1P/D1D1N, D1D2P/D1D2N thru D9D1P/D9D1N, D9D2P/D9D2N (differential video channels, as noted above)
• IVCC
• IVCC28
• IVCC18
• IVCC12
• VSYNC
• CSCL
• CSDA
• TEST_EN
• BIST
• FSS
• FLK24
• VGL
• GMA1 thru GMA14
• LOCK_FB
• VCOM_OUT
• WP_PGMA
• SCL_P
• SDA_P
• PVDD_O
• PVDD_E
• GCLK1 thru GCLK4
• VDD
• VST
• DSC
• VGH
• SDA, SCL, WP_GND (near the EEPROM on the component side)

Some of these pins seem to be pretty self-explanatory (SDA/SCL/WP, for instance).  Also, the “IVCC” pins are obvious.  These pins indicate that there should be a 2.8V, a 1.8V, and a 1.2V rail.  Probing these pins did not immediately yield these results, which merits discussion.

In the previous post, I applied 3V to the panel, which I figured would be enough to activate the switching power supplies on it whether they were meant to run on 2.5V or 3.3V (the latter being extremely common, and the former starting to gain traction in newer panels).  It was unusual to find the panel fading to white.  Per the eDP specification, the panel should be continuously refreshed to black with no signal driving it, so something seemed to be wrong.

There appear to be around a half dozen voltage rails on this board.  Testpoints break out input voltage (point IVCC) as well as 2.8V (IVCC28), 1.8V (IVCC18), 1.2V (IVCC12), -6V (PVDD_O and PVDD_E) and 20V (VGH) (more on those two some other time).  But the 1.2V and 2.8V testpoints appeared inactive.  Both of these supplies appeared to be driven by mystery-chip GD=EC on top.  Thus, my immediate theory became that the DP635 relies on the 2.8V and/or 1.2V rail, and the fading to white is the (powered) LCD glass resetting as it is not being actively driven to black.  Why white I don’t quite understand yet since IPS is naturally black, but let’s ignore that for now.  I increased my input voltage to 3.3V at this point, which seemed to make no difference.

I began to suspect that GD=EC is a dual buck regulator, based on the testpoints underneath it and the general layout of the components.  I probed the components and ended up with a schematic that appeared to agree.  I noted before that I suspected the part was a Richtek regulator, which came to me when I found a teardown of another product which had a confirmed Richtek part with a similar marking.  Now armed with the fact that the part is a dual buck regulator, and that it comes in a 10-pin 3×3 DFN, this was enough to track it down – the part is a Richtek RT8035 (Datasheet).

From the datasheet’s pinout (which I had already mostly figured out from probing the surrounding components), I located the device’s Enable pins and noted that the voltage measured here with 3.3V provided by the source was around 1V, which according to the regulator datasheet is between the Enable and Disable voltage limits, which puts it somewhere in a possibly-undefined region of operation.  In fact, probing the outputs of the regulator showed that there were occasional pulses of voltage produced.

Well, if it was a 2.5V panel it wouldn’t have these problems at this voltage, so that idea was discarded.  If this is indeed a 3.3V panel, it should be safe to apply up to 3.6V or so.  So I applied 3.5V to the panel, and lo and behold, the panel turned black, the current draw increased, and upon testing all the supplies appeared to be online.

I did a little more investigation, since that seemed a strange operating voltage, and noted that I was actually losing quite a lot in my wiring.  Even the two feet of 22AWG I was using was dropping one or two tenths of a volt.  When compensated for that, the panel seemed to run on 3.3V – but only just barely.  It is hard to believe that it is actually a 3.3V panel, it seems to have almost no bottom-end voltage tolerance.  My rational side says the panel should easily run on something higher than 3.3 – maybe 5? – since all of its important circuitry appears to be powered on switching subregulators and not from the incoming VCC.  But I can’t bring myself to smoke an otherwise working panel, so for now I will set my supplies to 3.5V and call it good.  Plus DisplayPort runs on 3.3V and the pullups and pulldowns might use the input rail, so we don’t want to go too high.  For what it’s worth I have not seen any other Apple LCD product use a logic rail above 3.3V – not to say that it isn’t the case, but it would be uncommon.

So now the panel was running, drawing about 600mA at 3.3V (for what it’s worth, it only drew about 200mA when it was misbehaving and showing only white).  That’s about 2W of panel drive power, which sounds about right.  It might rise slightly when driven under certain circumstances.  Neat!  Let’s do something with it.

To go any farther, I’d have liked to use a breakout cable to avoid having to solder to the panel itself.  But what the hell, I’d already soldered on it a ton to remove the shields and to install some power and test jumpers, so what had I to lose.  Assuming from the block diagram of the DP628 (remember that?  I’ve rambled a lot since then!) that the DP635 takes in DisplayPort, and remembering from the DisplayPort specification that the DP lanes and AUX pins are capacitively coupled, and additionally that AUX and HPD have pullup or pulldown requirements, there will need to be a group of capacitors and resistors somewhere on the board that correspond to the requirements of the specification.  Suspiciously, next to the DP635 appears this formation of components:

The reference designators for these parts are listed off to the side – from top to bottom, left then right, the components are R47, R48, C75, C76, C77, C78, R49, then C69, C70, C71, C72, C73, and C74.  These are seriously small 0201 parts.  I noted in the last part of this writeup that I’d located the DisplayPort lane pins on the connector.  To confirm that these components are related to DisplayPort, I probed for continuity between here and the connector, and indeed they appear to be.  What’s more, R47 and R48 are 1Mohm resistors connected to capacitors C69 and C70; one resistor pulls to GND and one to VCC.  This precisely matches the description of the AUX channel.  Probing the center of the the series set, we can finally confirm that pin 11 on the I-PEX is AUX+, while pin 12 is AUX-.  Continuing in order, pin 14 connects to C71, pin 15 to C72, pin 17 to C75, pin 18 to C76, pin 20 to C77, pin 21 to C78, pin 23 to C73, and pin 24 to C74.  We still don’t know what order the lanes are in, but at least now we know the correct connection for AUX.

The advantage of knowing AUX is that now we can start connecting the panel to a PC and can see what Windows thinks of it.  By wiring the panel to a prototype of my Simple iPad Breakout (only for the DisplayPort connector) and shorting HPD to VCC, I got the panel to register as a 2880×1800 “Color LCD”:

Hooray, it’s alive!  When I was dealing with the white-screen issue I wondered if the damage to the PCB visible next to the DP635 had rendered the panel an expensive paperweight.  Now the effort is only figuring out the ordering of the lanes and the location of HPD, both issues which would be simple with a breakout.  For HPD, we need only measure which of the remaining unknown pins (9 and 10) goes logic high when voltage is applied.  For the lane ordering, there are only four probable orderings (0-/0+…3-/3+, 0+/0-…3+/3-, 3-/3+…0-/0+, 3+/3-…0+/0-), and with a breakout and jumper wires this should be found very quickly.

I got impatient and soldered in 36AWG magnet wire jumpers on all the lane lines, and tried a couple of the arrangements but have not yet been lucky enough to land on the correct one.  I’m not sure I’ll continue with this though – it’s massively frustrating, and I’m not even sure this panel is operational nor whether my soldering to the tiny capacitors makes a good connection.  It will take another two weeks, but I think I’ll just wait until I get in the corrected breakout boards to continue down this path.

In the meantime I have been working on the backlight driver for the panel.  For the iPad panel, I used a Linear Technology LT3754 16-channel driver with integrated boost supply.  I like the concept of using drivers with internal boost supplies – one less IC to buy, and a decent savings of board area.  When you bump up from seven to sixteen series LEDs, the number of drivers that are capable of boosting to the necessary 51V or so internally is not quite so large.  The ‘3754 and its max 45V output is no longer usable.

I think for this panel I will be investigating the Freescale MC34844A.  This part is a 10-channel, 60V, 80mA/channel driver which can modulate based on analog input, PWM, or (interestingly) an I2C interface.  There exists a simpler 6-channel version of this chip, the MC34845, and I briefly considered using it, but despite the nicety of being a slightly simpler chip, the ’45 is Not Recommended for New Designs (is going end of life soon) so I dare not use it.  The only real downside of the MC34844A is that it only supports up to 28V input.  I’m a big proponent of hugely overdesigned voltage input overhead, because people do terrible things to electronics sometimes, and I liked the fact that the 3754 could work all the way up to 40V “just in case”.  So this version will only work to 24V, oh well.  I suspect most people would run it on 12V anyway so maybe I am needlessly cautious.  I already have parts for the new backlight driver, so as soon as I spin a board for it I can try everything out.

Holy cow, that’s a lot of words that don’t really have a lot of useful content.  I’m really feeling a setback since I built the first breakout around an incorrect connector.  But I’ve got the correct board in the works, and will order it on Monday, and hopefully by mid two weeks from now I’ll have a proper board and will have the panel running.  At least that’s the grand plan – I don’t guarantee I won’t screw up again… it’s a good thing OSH Park is so cheap!

In the meantime, off to work on the iPhone 4 LCD… stay tuned for that in a later episode.

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The Revision B boards for the simple iPad Retina LCD breakout have arrived.  As I mentioned last time, this version fixes the mis-numbering of DisplayPort lanes that was present in Revision A.  A few additional tweaks were also made.  Take a look at the previous part for a more complete summary of the changes.

I have built up one board and tested everything out, and luckily this time everything seems to be working great.  Have a look:

I noted in the comments for the previous part that I was attempting to etch stencils to speed assembly.  Using the method outlined here, I attempted about 20 times to reliably etch a stencil from a soda can, trying various transfer papers, heat/pressure application, and printer settings, and I never landed on a particularly reliable method.  The problem is that the pins on the connectors of this board are really small (FFC) or really close together (DisplayPort), and the ratio of depth to web thickness means it is very difficult to etch enough from all areas without overetching any others.  I finally landed on one that was halfway okay, but I still spent a lot of time pushing paste around with a toothpick.  If I knew I was going to have to build a few more of these, I’d definitely order a professionally-made stencil.

But now that this board is on the shelf, I need to shift my focus to the “real” iPad interface, which has more or less taken a backseat lately, so feel free to take this design and order your own, modify it to suit your needs, etc.  I also have some boards and stuff left over if you don’t want to buy your own directly (even though three boards is only $10 from OSH Park).  Shoot me an email or leave a message if you want something and we’ll see what we can work out.

I’ve re-linked the board documents here.  Do with them as you see fit.  Happy hacking!

• PCB10002 REV B GERBERS (22K ZIP)
• PCB10002 REV B LAYERS (253K PDF)
• PCB10002 REV B STENCILS (1.1K ZIP)
• SCH10002 REV B (201K PDF)

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