Miscellaneous updates, 2015-01-31

Well, this is embarassing.  So much for my minimum-one-post-per-month goal.  Between working on the new house and real salaried work and some contract work on the side, I haven’t had a lot of time to post anything useful here lately.  Believe me, I’m just as disappointed as you are.  But never fear, I’ve just sent a new batch of boards off to be manufactured.  These boards are related to a previously-undocumented new project I’m working on, so there’ll be some new and interesting stuff to post in just a few short weeks.  Hopefully.

Beyond that, I’ve got some sort of left-field development I’m about to start on – a departure from the display stuff that’s gotten kind of repetitive for me.  As usual, stay tuned.

Miscellaneous updates, 2014-09-07

Good day all,

Just a quick note to reassure you all that I’m still around.  As alluded to in the previous post, in July we bought a new house, which happily has plenty of space just waiting to be adapted to a well-equipped electronics lab.  Before I can get back to hardware design, I’ve got a lot of work to do – all my test equipment and projects-in-progress are still spread amongst dozens of storage bins.  The lab, a previously unfinished area of the house, needs lighting installed and electrical and data wiring run in addition to furniture and storage needs.  Getting the lab up and running in full capacity is my immediate concern, and I appreciate everyone’s patience during this process.  Updates on the projects on this site to follow… someday.

Miscellaneous updates, 2014-06-24

Hello all!  I apologize for the long time without updates.  Paying work has kept me busy enough that I haven’t had much time to work on this stuff for the past couple months.  I don’t have any new information to give, actually, just wanted to say that no, the site is not dead, I’m still here, just busy.

What I do need to say is that I will be moving sometime in mid to late July, and with me will come the server that this site runs on.  This means there may be up to a week of downtime while service is transferred to the new house and everything is set up.  Be patient, I’ll come back, I promise!

[EDIT 7/9/14] Oops… the move hasn’t happened yet, but the site’s been down for a while (days? weeks? I’m not sure) due to an IP reassignment that didn’t get propagated to the DNS.  Sorry about that.

[EDIT 7/17/14] Server move is complete.  Hooray!  Now, to move my test equipment so I can continue working on these projects…

New project: Slightly-Less-Simple Retina LCD Adapter

As many have noticed, I’ve stopped offering my Simple iPad LCD Adapter for sale.  The reason I’ve given is that I am working on an improved version of the board.  Well, as of today I’ve gotten far enough on the design that I’d like to share it.

The new Simple Retina LCD Adapter, work-in-progress.

The new Simple Retina LCD Adapter, work-in-progress.

The most drastic change for this design is the integration of buck and boost power supplies to drive the panel and backlight respectively.  I was not happy with telling people they’d need to provide their own regulated power – the panel isn’t THAT sensitive to voltage wobble, but it can be a problem with particularly long power leads, despite the large hold-up capacitor.  Now the board should be able to take between 5 and 18 volts and spit out well-regulated rails.

Several other things have changed as well.  I’ve changed the full-size DisplayPort connector to a miniDP connector, because for as small as the board is, the full-size connector was a waste of space.  I’ve added a proper connector for power – while handing out boards with bare wires soldered on was functionally workable, it’s not exactly as clean a solution as I prefer.  There is no longer a diode OR between external and DisplayPort power, because cables that carry DP_PWR are so uncommon that it is unnecessary.  And there’s a fuse, to limit catastrophic failure in the event of a solder bridge or improper installation.

Now, the added components will increase BOM cost – I’m not sure by how much, but I know it will.  However, I have designed in jumpers that will allow users who still want to feed in their own 3.3V and who don’t need a backlight supply to use this board in the same way as the old one.  Hopefully this will make the design more accessible to people who want a more compact, all in one design without alienating those who like it how it was.

The design is a day or two from completion.  As per typical, I’ll be building a board up and debugging it before I release the design documents, so that I don’t release something that won’t work.  So keep an eye out in the coming weeks.

Miscellaneous updates, 2013-12-04

Oops!  I told myself I would update this site at least once a month.  As you can easily see, I haven’t quite kept up with that desire.  Things have picked up in my professional life and I have not had nearly as much time lately to tinker with this stuff.  But here’s what’s going on.

  • iPad simple interface:  Currently out of stock.  I’ve sold all of my first-run boards and have not ordered more.  Sources for some of the components used have dried up, and I may need to change the board to accomodate replacements.  Additionally, based on the results of the Macbook board, I might want to add some small power supplies to the board to alleviate the need to provide two precisely regulated rails.  There is currently no ETA on this.
  • Macbook board:  Hasn’t been touched since the previous post.  Lack of time, unfortunately.
  • iPad digitizer research:  Starting up again.  The next “real” post may well be on this topic.
  • Other in-progress projects:  No further progress.
  • Metalworking:  I am now the proud owner of a Precision Matthews PM-932M mill/drill machine, so one of these days I’m planning a new series on making metal widgets.  Stay tuned for that.

Also please note:  The server on which this site resides is due for major hardware changes in the next week or two.  Expect downtime of up to a day or two while new hardware is installed and configured.  I suspect I’ll be too lazy to put up a “down for maintenance” message, so this will be the only warning.  Don’t worry, unless there’s some major hardware issue the site will be back soon.  [Edit: Complete.]

So that’s where I’m at.  No real news to pass, but it’s high time I posted “something” so folks don’t think this site is abandoned.  Hopefully the new year will bring more time to work on some of these in-progress half-finished projects.  We’ll see.

Hacking the Macbook Pro Retina LCD, Part 4: First PCB Tests

Welcome back!  It’s been more than a month and a half since my last post on the Macbook Pro Retina panel – damn my “real job” and the time it consumes.  But we’re here now, so let’s dive into things.

In the previous two posts on this subject, I have talked about two boards that I have been developing for the 15.4″ Macbook Pro Retina display assembly: a breakout for the FaceTime camera, and the main display controller / backlight driver board.  Well, in the month-and-a-half that has elapsed, both boards have been received and built.  Let’s start by taking a look at the former.

Camera Breakout

When I went to order these boards, I did so immediately after the cutoff for the current OSH Park 4 layer order, so the estimated delivery time was three or four weeks.  Unhappy and impatient, I held off and instead ordered the board as 2-layer for more instant gratification.  The two inner layers are only GND, so this is possible without too much trouble.  It throws off the impedance of the USB traces probably significantly, but as the entire trace length is a half inch or so, I figured it’d be close enough for at least temporary use.

So the boards arrived a week and a half later.  I immediately noticed something interesting and bothersome.  Board fab houses typically require a gap between the edge of any copper and the routed board edge.  If you are making a small board and including mounting pads for screws, the pads may consume a large percentage of the total board area – in fact, the pads may well drive the overall dimensions of the board, and larger dimensions mean greater board cost.  I wanted this board to screw mount, but even the 2-56 screws I designed for needed quite significant pads.  I decided it would be nice to trim the amount of room wasted on mount pads by clipping the pads at the board edge, allowing the screw to extend into the no-copper area at the edges of the board – it really only drops a few cents from the board in this case, but it makes me feel better.

So in Altium Designer, I made a small Pad on Multilayer (the magic layer which is copied to all other layers), then made a Polygon in the shape of a circle with a flat edge and also placed this on Multilayer.  In theory, this should have resulted in a round pad with a flat edge, drilled and plated through as expected – in fact, the 3D render of the board shows this:

For a sense of scale, remember that that's a miniUSB...

Mount pads look OK here.

But what arrived from the fab was this:

There aren't supposed to be voids in those mount pads...

There aren’t supposed to be voids in those mount pads…

When I poured the rest of the GND polygon, apparently Altium attempted to connect to the inner Pad, and generated Polygon Cutouts surrounding it, which happened also to cut the Multilayer polygon.  It didn’t show in the PCB editor, although it did in the Gerbers – but I was in too much of a hurry when ordering to notice.  Oops.  But so be it, it’s only the mount pads.

I then assembled the board, and with bated breath, plugged it into a USB port.  And Hooray!  The Device Connected sound sounded, and the camera showed up in device manager.  But, strangely, the power LED was orange.  I specified a green LED, I thought I placed a green LED, but it was bright orange.  I checked the package to be sure but it was correct.  It was then that I discovered a tiny short, and simultaneously learned that if you apply 5V directly across a 2.1V green LED, it becomes an orange LED.  Neato!  It also gets real real hot.  But miraculously, after I corrected the short, which had caused the full USB voltage to appear across the LED, it returned to green and operated as normal.  So I guess I can say, these OSRAM CHIPLED parts seem to be pretty hardy!  I unfortunately don’t have any photos, but these parts are cheap, so buy some and experiment for yourself.  Science!

After a few days the 4 layer board order deadline had arrived again, so (having not discovered nor corrected the pad issue) I re-ordered the board as 4-layer, this time adding a second transient suppressor for the ALS connector… because why not, and you can always short it with jumper wires if you don’t want to use it.  So here’s what that looks like (note that I have fixed the pad issue at this point):

Yep.

Yep.

I haven’t bothered to build this one yet, but it hasn’t changed significantly since the 2-layer version, so I suspect it’ll work fine.  The files for this board can be downloaded here:

Enjoy!

Main Controller Board

Now, the information you’ve all been waiting for.  As I said on the previous post on this subject, I quickly threw together this board to get it in before the following OSH Park cutoff.  As such it’s not perfect, but it is fairly functional (or so it seems from the minimal amount of testing I’ve done so far).

There’s a lot of new stuff going on on this board, as compared to my iPad board (on which this one is loosely based).  Of course the panel output connector is different, because the panel is different.  Also, though, the barrel jack has been removed, and a 2-pin shrouded connector has been added in its place.  Barrel jacks, I finally came to realize, are just too damn big and expensive for a little cheap board like this.  The new solution is less than a dollar in single quantities for plug, receptacle and terminals, whereas the board mount barrel receptacle was more than a dollar by itself, not counting wire mount plug.  Plus the barrel jack tended to be the tallest component on the board, driving enclosure dimensions.  It takes a bit more work to implement, but I still think this was a good change.

The dc-dc converters are new as well.  The board contains two dc-dc buck regulators, both based on the AOZ1281 from Alpha & Omega Semiconductor.  This part was chosen due to very low cost – about $0.90 in single quantities – as well as ample output current (1.8A) and acceptable input voltage range (3-26V).  The board implements this part as one 3.3V/500mA converter and one 3.8V/1A converter, the former for processor, indicators and other functions, and the latter for the panel itself, which was investigated and found to run well on 3.8V in a prior post.  It’s probably a 5V panel, in retrospect, and I may someday become ambitious enough to test it at this higher voltage, but for now 3.8V works.

The board shares the same Freescale MKL25Z128VFM4 processor as the iPad board, again due to cost to performance ratio of the $3 ARM Cortex-M0+ core.  Sure, I could drop $0.50 and put in a MSP430, but I like the potential for other functions that the more powerful processor enables.  I still need to learn how to program the damn things, but I digress.  The other big IC on the board, the backlight driver, has completely changed compared to the iPad version.  Whereas the iPad panel has 12 backlight channels at 20V apiece, the Macbook has only six channels but at some 52V.  The LT3754 used on the iPad board only does 45V, so a new backlight driver is needed.  Of the (relatively few) integrated boost converter / LED driver ICs, the best choice for this application seemed to be the Freescale MC34844A, which happily will push out 60V with appropriate configuration.

In the interest of keeping this post from being more than fifteen or twenty pages, I’ll leave the rest of the description to the schematic, but if anything is unclear please feel free to drop me a comment or email.

Again, this board uses 2-56 mounting screws, and again, I opted to include clipped pads.  And again the boards showed up with voids in the pads.  But this time, inexplicably, some of the pads did not have voids.  They were all created the same way so I can’t quite explain that one yet.  But one thing is for sure, I’ll certainly pay more attention from here on out.  I built the pads for one of my boards at work with clipped edges as well, but this time used top and bottom polygons instead of one multilayer one.  In this way the pads are slightly smaller in the internal layers, but on the other hand the polygons connect without issue, so that’s a small price to pay.

Anyway.  Here’s the (99%) finished board, lacking only a fuse and transient suppression diodes in front of the USB port and DP connector:

Top.  Ignore the soldered-on power wires...

Top. Ignore the soldered-on power wires.

Bottom.

Bottom.

I’m not 100% happy with it – in particular, I suspect that my overzealous attempt to match the lengths of the DisplayPort lanes may have actually had an adverse effect on signal integrity as the traces have to bend a whole lot and come in much closer range of each other than is really recommended.  But I can say that the board works like this, and I can’t keep from releasing something forever because I’m not 100% happy with it (or so my boss always says – “You can always fix it in Rev B”).  So here we are.

Now, the processor has control over panel power and backlight on/off and brightness, so without programming the processor the board won’t do anything.  So, still lacking much experience with the ARM Cortex-M0+ platform, I wrote a very barebones program that simply turns on the power and backlight driver for the panel, and additionally powers up the PWM controllers for the offboard indicator LED.  So here’s the board documents, and the source to at least power-on the necessary systems:

Holy cow, I just realized I never released the documents for the indicator/button board either!  Well, let’s go ahead and do that now too.  Here’s what it looks like:

Pretty simple.

Pretty simple.

This board is designed to be double-stick taped directly to the back of a panel at an edge of your choosing (my preference is bottom-right) and connected to the main board via a wire harness.  Some of the other controller boards out there with buttons onboard have very awkward button placement, so this is a slightly more expensive but much more elegant solution.  The files for this board are attached here:

Whew.  This has been a grueling post to prepare.  Enough for now.  Er, except for one last picture!

Woohoo!

Woohoo!

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Miscellaneous updates, 2013-08-27

It’s been quite a long while since I’ve posted anything, so I just wanted to put something up to reaffirm that I’m still here :)

It has been a busy few weeks for me in the world  outside my workbench, so progress has been slow on the active projects.  Here’s an overview of what’s going on:

  • Macbook “full-featured” controller board:  Boards hare arrived, waiting on component delivery (due Thursday).  This will include demos of some new and lower-cost components which will eventually make their way into other boards.
  • iPad “full-featured” controller board:  On hold pending redesign for cost reduction and results of Macbook hardware evaluation (as much of the hardware is shared).  Will leapfrog the Macbook and iPad boards until I am satisfied with how they work.  Also am working on the software for this board.  I’m really trying to get a USB firmware update utility built, but I’m new to the Kinetis platform so I’m having some trouble.  Has anyone out there built a DFU loader for a KL25 that can share some pointers? :)
  • Macbook camera board:  I ordered a 2-layer version (inner layers are all GND) some weeks ago to test, and that worked fine.  Now the proper 4-layer boards are in and I need to build one of those up.  But I’m satisfied with the design in general so I should be releasing those documents as soon as I get the ambition.
  • iPad touch panel:  Oof… haven’t touched that one for a while.  Need more free time…
  • Reflow oven:  I found some proper convection-type ovens at the local Wal-Mart for around $40 which will save me plenty of work in installing my own stir fan, so I may well be starting over.  For now I’m getting too comfortable running the boards freehand with a temperature probe though…
  • LP173WF2: Working on an interface board to take advantage of the connector hack I implemented.  In progress, no ETA

So that’s that.  Not much to show at the moment.  But hopefully that’ll change this weekend when I get some work done on the Macbook boards.

Plus!  I just this weekend got my new milling machine up and running!  So expect some metalworking projects to start showing up from time to time.

That’s all for now.

[EDIT 9/9/13] Hey, progress!

Good ol' high-definition Futurama.

Good ol’ 2880×1800 Futurama.

The Macbook board mostly works!  Backlight driver is putting out on the low side of its designed voltage and the firmware is only complete enough to force everything on, but other than that, it seems to run pretty OK.  Full post on this hopefully tomorrow.

Hacking the Macbook Pro Retina LCD, Part 3: First Working Demo

After screwing up and designing boards around an incorrect connector, and then when the corrected boards came in immediately leaving town for a week on business, I’ve at long last had some time to work on the Macbook panel.  Spoiler alert:  Some progress has been made.

If you don’t recall from previous posts, I threw together a quick board containing only DisplayPort and I-PEX connectors and a bunch of pin headers between them.  The idea is that since we know where the DisplayPort connections are but not the order in which they are arranged, we can solder in jumper wires very easily to test the various lane orderings and polarities without having to otherwise modify the board.  Here’s (the fixed Rev B version of) the board I used to figure out the pinout:

Assembled test board with all wires attached.  I unfortunately don't have a photo of the board prior to installing the wiring.

Assembled test board with all wires attached. I unfortunately don’t have a photo of the board prior to installing the wiring.

There’s nothing special going on here.  At top, connected to the panel, is the I-PEX connector, with its known power and backlight pins hardwired in.  At the bottom is a standard mDP, connected to the host PC.  I connected all the wires I could – power and backlight of course, and AUX+ and AUX-.  From there some engineering is required.

First, we look for Hotplug Detect.  This pin should go logic high shortly after power is applied to the panel.  There are only two pins left on the connector without a defined purpose, 9 and 10.  In testing the panel, it is observed that pin 9 develops 2.8-3V, and pin 10 develops 1.4-1.7V.  The latter is a bit low for HPD, so we will assume that pin 9 is HPD and pin 10 remains unknown for now.

With that pin now connected, we begin testing the DP lanes.  Remember that logically, the lanes should be arranged in one of four orders: 0+/0-..3+/3-, 0-/0+..3-/3+, 3+/3-..0+/0-, or 3-/3+..0-/0+.  I started with the first ordering listed.  Interestingly, the display showed a half-inch of garbled blue blocks at the top and gray bands down the rest of the surface, but the display announced itself to the PC properly and I was able to set its properties.  More boggling yet was that when I reversed the polarity of each of the four pairs, I got a different garbled top area (this time more like static) and the same gray bands, but equal operation with the PC.  I had always assumed that the incorrect polarity would result in a completely inoperable display – interesting.  But not yet correct.  I tried the other two combinations, and neither of those would even bother to talk to the PC beyond sending EDID.

I panicked for a second here, thinking I’d have to try a lot more combinations of pinouts, taking a lot more work.  I tried just connecting one, two or three lanes to see if that made any difference but the PC was unhappy with all of these tests.  Finally I happened to glance at the analog ammeter dial on my bench supply and it was wiggling fairly wildly around the 300mA range.  This didn’t seem right at all, and I immediately began to suspect the power I was applying to the panel (through about three feet of jumper wires to place it close enough to the DisplayPort source on the other side of the room).  When I replaced the original pinout (with the blue blocks) and used about 8″ of hard-soldered wire and a local bench supply, and upped the current limit to about 1A, I was greeted with the following!

It works!

It works!

This just goes to show you how important it is to pay attention to the impedance and voltage drop of your wiring.  Always use as short of wires as possible!  Do note that I only connected one backlight string, which is why the banding is so bad; with the other five strings connected it probably wouldn’t be noticeable.  It looks a little dark because I don’t have proper current limiting installed and I’m driving it cautiously.

So now we know the full pinout of the Macbook Pro 15.4″ panel (or, at least enough of it to get it running.  Here it is, for your design and hacking purposes:

Not sure what Pin 10 is.  Looks kind of like 0.5*HPD

Not sure what Pin 10 is. Looks kind of like 0.5*HPD

Finally knowing the pinout, and running short on time before the next OSH Park 4-layer order, I quickly made up a proof-of-concept controller board for the panel.  The board includes a Freescale MC34844A backlight driver, a Freescale Kinetis MKL25Z128 ARM Cortex-M0+ processor (again chosen for cost to performance ratio), independent switching supplies for the processor and for the panel (which requires a different voltage), mini-USB and mini-DisplayPort connections to the host PC, and a header to match the header on the camera board for the ambient light sensor.  Special care was taken to cut costs on this board wherever possible without compromising functionality – the Linear Technology switcher from the iPad board was scrapped for parts a third of the cost, and some parts were increased in size to avoid paying the premium for the size decrease.  With some difficulty the board was kept to the same compact 1.5×2.5 inch form factor as the full iPad board.

I don't have many of the parts modeled yet.  So sue me, I was in a hurry!

I don’t have many of the parts modeled yet. So sue me, I was in a hurry!

I will release the documents for this board as soon as I build one up and verify that it works – I don’t want anyone ordering a board which might not work.  If you still really want them ahead of time to look at, send me an email.

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A Compact FullHD 120Hz 3D Display, Part 1: First Looks

Last week I wandered across a thread over at the Overclock.net forums talking about my iPad controller boards.  It would seem there is a growing demand for ultra-high-resolution multi-panel displays amongst the gaming and power user crowd.  The recent releases of high-pixel-density panels in consumer devices means they have become quite accessible to the average hobbyist.

There are a couple of niches that these panels best fill.  For the road warrior, the compact size of the iPad panel might be nice.  For the graphic designer, the Macbook Pro Retina panel offers good performance.  But for the gamer crowd, where high refresh rate is most desirable, neither of these panels quite fits the bill.

As it so happens, boutique PC manufacturer Alienware continues to push the limit (and budget) of the gamer-on-the-go.  Enter the Alienware m17x, a megalaptop with an optional 17.3 inch, 120Hz, full HD 1080p, 3D-capable display.  That’s an awful lot of display, and found in its native habitat the privilege of using it would start at $2000, but thankfully we can find replacement panels in the usual places for about $100.

Now, 1080p doesn’t really hold a candle resolution-wise to some other panels such as the Macbook Pro Retina display at 2880×1800.  But the major advancement here is the 120Hz refresh rate, which promises to offer better gaming performance and less video tearing.  I don’t game much, but I was curious about the combination of features in this panel, so I bought one to play around with.

The panel in all its glory.  Note that I'd already removed the square of conductive shielding cloth before this photo was taken, which is why it is wrinkled.

The panel in all its glory. Note that I’d already removed the square of conductive shielding cloth before this photo was taken, which is why it is wrinkled.

This is the LG LP173WF2(TP)(A1).  We can pull all the necessary specifications from its datasheet (mirrored locally here).  It is driven with 4-lane Embedded DisplayPort, just like the Apple Retina panels.  However, interestingly, this panel is driven with 5 volts, instead of the typical 3.3V.  Further unexpectedly, the panel electronics draw a shocking 2.3 amps (11.5 watts), which does not include the backlight.  I bet the stock 86Whr battery in the m17x doesn’t last very long.

Speaking of the backlight, a notable difference between the Retina panels and this panel is that the LP173WF2 contains onboard backlight drivers, eliminating the need for external drivers.  SImply apply between 7 and 20V, a logic-high Enable signal and a 5-100% duty cycle square wave, and the rest is taken care of.  The backlight claims to draw another 11.6 watts.  Here are some high-resolution shots of the panel’s backlight drivers and controller electronics:
LP173WF2_Controller_1LP173WF2_Controller_2LP173WF2_Controller_3LP173WF2_Controller_4LP173WF2_Controller_5

Just like every new display, this panel has a different set of power and control requirements to all the others.  Thus, a new controller board will be designed to fit the particular needs of this unit.  But we’ll get to that in due time.

First, let’s take a closer look at what we’re working with.  Seemingly similar to every other panel, this one has a unique connector and pinout.  In this case it is a JAE FI-VHP series 50-pin connector, FI-VHP50S-A-HF11, mating connector FI-VHP50CL-A.  This is a problem for a couple of reasons – first, this appears to be a new part which is not currently available at any of the usual distributors, second, even if we could find it, it’s probably beyond the capability of most folks to populate the 0.5mm pitch connector with the very small (32-42AWG), preferably shielded coaxial wires.

So what do we do?  We could order a reel of 3000 pieces direct from JAE for some thousands of dollars, but that’s not a wise investment unless we’re likely to use a couple thousand pieces, and then we still need to assemble the harnesses (and soldering 50 tiny wires on 0.50mm pitch won’t be fun).  We could draw up a specification and order custom harnesses from a supplier, but still unless the quantities are quite high they will probably be more expensive than we’d like.  We could buy used assemblies from the source laptop on eBay, which we can get in single-piece quantities, but these are not very prevalent and are extremely expensive.  Or we could replace the connector with a more widely-used type, which requires us to modify the panel but is comparatively very inexpensive and easy to come by.  I have opted to take this last approach initially, and will reevaluate the other options if demand arises.

Originally I contemplated designing a flex circuit harness to solder directly to the panel and break out into an iPad-style 0.3mm contact pattern.  I still think this would have been a fairly slick solution, but when I attempted to draw it up I found that this contact pattern is not possible for the low-cost prototype houses to produce – the traces are too small and the pads are too close together.  So as a runner-up option I have chosen to replace the existing connector with a 0.5mm ZIF FFC socket, FCI 62684-501100ALF.  By using a standard connector like this we can also use standard FFC cable assemblies, which are very inexpensive and come premade in a variety of lengths.  I bought a 2-inch cable which seems about right.

Original FFC concept.  Ultimately this plan proved too complex for the "budget" flex board suppliers.

Original FFC concept, using my full-feature iPad board as a stand-in for the new board.. Ultimately this plan proved too complex for the “budget” flex board suppliers, and I was unwilling to pay for a “real” board house.

The downside to this approach is that since the VHP-series connectors have a 3-pin-wide break in the middle, the 50-pin connector is actually the width of 53 pins.  Luckily two of the pins on one side are No Connects, but we are still forced to choose between losing pin 1 (“2D/3D Contents Communication”) and pin 48 (DP Lane 3 shield ground).  I have opted to offset the connector to carry the ground connection, and will re-wire pin 1 to one of the three unused pins in the middle of the connector if I get around to it.  Actually if you look at the controller photos it appears as if pin 1 is connected through a non-populated resistor and is thus a no-connect, so I may not bother.

The removal of the existing connector took a surprising amount of effort.  The FI-VHP series has stabilizing legs soldered to the board on the three sides without contacts, so all four sides are soldered down.  This makes removal of the connector, particularly without harming nearby components, quite difficult.  To reduce heat transfer to the heat-sensitive plastic diffuser films, I propped the controller board up off the rear surface of the panel.  I would like to have flipped the controller board over and solder it against a flat surface to avoid stressing solder joints, but the board is held by a small jog in the plastic frame and I felt uneasy putting enough stress on the connecting ribbons to move it.

An embarassing amount of time later, the original connector was removed, losing only one mount pad and the two No Connect pads in the process (probably because my heat was too high):

Connector removed (but pads not yet cleaned), connector modified to clear U4, soldermask removed for side feet.

Connector removed (but pads not yet cleaned), new connector modified to clear U4, soldermask removed for side feet.

Now, to understand my next move, it is important to note my grand plan for this panel.  I’ll illustrate the plan with a 3D model as soon as I have time to draw something up, but for now words will have to suffice.  The panel will need to have a controller PCB attached, to generate the backlight dimming signal and break out the eDP to a more accessible connector.  The various connectors required and the cables attached to them are bound to be heavy, so I don’t want to attach my board to the thin plastic protective sheet over the LCD controller.  I’d much rather stick it directly to the exposed sheet steel chassis.  To achieve this the ribbon cable must point up.  I could either accomplish this by putting a sharp bend in the ribbon cable, or by populating the connector upside-down.  The latter option has the disadvantage of interfering with one of the eDP ESD protection diode arrays, but it provides the benefit of also allowing me to solder down the outer feet to provide strain relief to the tiny solder joints.  This is ultimately the path I chose.

I scraped away some soldermask to make pads for the connector’s feet, and trimmed off the corner of the connector and latch to clear the protection diode.  Then, time to solder the pins.  I had some trouble getting the solder to flow between pin and pad – because the connector “only just” fits behind the diode, there is almost zero exposed pad behind each pin, which means there is no rear solder fillet to span the gap.  Probing the pins with a dental pick after the first pass noted several wiggling pins, on which solder had flowed over and up the pin but not down around it.  I went back and pressed down on each pad while applying a little more solder and that seemed to fix things.  And after more time than I am comfortable admitting to, and on my third connector after ruining two, it was finally done.  Here’s what it looks like now:

Looks pretty good, if you don't look too close.

Looks pretty good, if you don’t look too close.  Don’t let the photo size fool you, those pads are really really tiny.

Ultimately I was unable to reflow it with hot air and unable to solder it with the finest tip I had on my home soldering iron so I had to take it to work and use the professional soldering station there.  I often say that the things I design are difficult to build up, but for some reason – probably due to the delicateness of this assembly – this one was the most difficult soldering job I’ve recently had to do.  I sure hope a source for the correct connector appears, because this was no fun!  Actually, to be fair, after I started using the pro soldering station things went a whole lot better, so maybe if you have good equipment it’s doable.  But it’s certainly no cakewalk.

That’s about all I feel like doing for now.  I now need to spend some time hacking the other end of the ribbon into one of my iPad or Macbook boards in order to apply power to the panel.  As a happy accident, as I noted in an earlier post, I have a set of boards that I designed erroneously to break out a 0.5mm connector which I thought was used in the Macbook, so maybe I can leverage those to get up and running faster.  We’ll see.