Having multiple monitors is a great luxury. Not everyone appreciates it, but those that get used to it miss it greatly when traveling. It’s the biggest downside of using a MacBook Air as the travel laptop. It is smaller and lighter than the homebuilt external monitor, making it kind of silly to use them together. When light weight and portability is important enough to take the MacBook Air, we’ll also need the external screen to be equally portable.

The search for a thin-and-light external screen companion started with units that receive both power and data via the USB port. Sadly most of them offered only a low 1366×768 resolution at the starting $100 price range. Very few offer 1920×1080 resolution and they are in the $200 range. To get resolution any higher than that, we’ll need an iPad running Duet Display. Which means spending >$300. The good news is, for that price, the system worked very well with only two caveats:

First, Duet uses a proprietary protocol that requires a special driver running on the computer to talk to the app running on the iPad. Installing this driver triggered several warnings from MacOS and required explicit authorization to run non-Apple code signed with the name Rahul Dewan. A web search indicated this was the name of founder and CEO of Duet Display, so that matches, but it’s still a scary action from a security perspective.

Second, application windows could not span the two monitors. They can be dragged from one to the other, but each window will show only on one monitor. If a window is dragged to straddle the divide, only half of the window will show on one monitor, and the other half is not visible anywhere.

Other than that constraint, Duet Display works well to make an iPad (2017, Model A1822) serve as an external monitor for a MacBook Air (13-inch, early 2014). The speed and responsiveness are great. So far, the performance has been indistinguishable from an external monitor connected to the MacBook Air via HDMI.

It even offers something not available on other USB external monitors: the ability to hook into Apple’s Touch Bar feature and show the bar on the iPad. Even for Apple computers that aren’t equipped with the Touch Bar.

Duet+iPad has turned out to be the most expensive of the external MacBook monitor options, but it makes a compelling case to justify its price. High resolution, super lightweight, and naturally the iPad is still a perfectly good tablet when detached from the computer.

 

Once we have a compact core built for the portable external monitor project, it becomes relatively easy to design and build an enclosure around it. Mostly an acrylic box that functions as a sleeve into which the core can fit, but also some additional components so we can have an integrated stand.

Once the individual parts are cemented together, a quick test to verify the parts fit.

Then we install the core.

Two problems were immediately apparent.

First problem: movement along the threaded rods were not constrained. In the ideal CAD world, the parts only hinged about a single axis. In the real world, they slide all over the place because I forgot to design in anything to prevent that movement.

Second problem: The threaded rod at the top did not function as designed. Not only did it fail to clip in to the top and hold things closed as I had hoped, it also blocked access to the ports in the open position.

To constrain movement along the threaded rods, I added a few 3D-printed parts to the base. I also replaced the upper rods of the stand with 3D printed parts for better alignment with the adjacent rail and eliminate the need for the threaded rod that ended up blocking the port. It still doesn’t clip to the rail and hold everything closed like I hoped, but it is a big step forward in functionality.

Once that is all done, the portable external monitor became far more portable. While maximum thickness stayed about the same, most of version 3 was thinner with only the main circuit board area reaching that maximum thickness. In contrast, all of version 2 were of the same maximum thickness. We shrunk along the remaining physical dimensions: the height shrunk by 1cm, and the width shrunk by a dramatic 6cm.

All of the above combined to allow PEMv3 to fit in my JanSport backpack. And carrying it will be far less of a chore now due to its significantly lighter weight. The fully equipped PEMv3 enclosure is now roughly half the weight at 4 lb. It is in fact lighter than even just the acrylic portions of PEMv2, which weighs in at 5 lb empty of electronics.

All those advances, and we have an integrate stand as well! Version 3 should be a far more usable unit than version 2 was.

Now that the unused bracket has been cut out of the way, it’s time to pack components into that newly freed space. Due to the CFL backlight power wire, there’s not a lot of room for creativity to place the CFL voltage converter board. It ends up approximately at the same place as the old dead CFL driver board where the bracket used to be. That left enough room on either side of the driver board: the buttons circuit board on the left, and the IR receiver on the right.

One unfortunate aspect of these aftermarket circuit boards is that they’re designed towards ease of construction, allowing easy mixing-and-matching components. Large components, especially the cable connectors, make it easy to snap things together. But the large connectors work against us when we’re trying to pack everything tightly. There’s a good reason they don’t use these types of parts when building thin and light laptops!

This hampers our effort packaging the buttons board and the IR receiver board. Everything is on one side of the circuit board for ease of construction, working against a compact layout. For example, we want the user-facing bits (buttons and IR receiver) on one side of the circuit board, and the cables on the back side for connection, but that’s not how they were built.

Building something out of laser-cut pieces means the Z axis is constrained by the thickness of the acrylic stock available. That plus the inconveniently placed cables and connectors made the whole exercise a challenging game of 3D jigsaw puzzle. Here’s my solution for Portable External Monitor, version 3:

While the components aren’t all on a single sheet of acrylic, we got close enough that it’s actually a pretty tightly integrated unit. Now this core unit, consisting of the screen plus supporting circuit boards, needs an enclosure around them.

For the portable external monitor project, version 3 (PEMv3) , we want to pack our components more tightly together to create a compact package. The most inconvenient barrier to the goal is the old back light driver board mounting bracket. While the circuit board itself was already dead when I got the laptop and promptly removed, the bracket for the driver board was still present during PEMv1 and PEMv2. The aftermarket back light driver board is significantly larger than the original Dell part and would not fit in the bracket. I had originally hoped the bracket can be recruited into a new role but none had ever come up.

So now it is time to trim off the bracket.

The front part of the bracket is riveted to the thin metal bezel of the LCD panel. The rivet makes it easy to remove with a Dremel grinding tool, but I was concerned about the potential for metal particles to damage the panel. I spent more time covering and wrapping the rest of the panel than I did removing the rivets.

The rear part of the bracket is part of the panel mounting frame. Since there were no electronics here, I didn’t have to worry as much about damage. I will need to thoroughly clean up the work piece afterwards to minimize the number of particles that are still sticking, but I didn’t have as much risk while doing the actual cutting.

I chose to minimize the cut length which removed more metal than necessary because the shortest cut connected the two large bottom holes. We should still have enough structural strength and mounting holes for the frame to be useful.

With the old bracket out of the way, it’s time to pack our components into the space previously occupied by the bracket.

 

And now, back to the portable external monitor (PEM) project. Version 2 has been in use for several weeks, called into duty when I needed a screen. It was used to help me install and smoke test ROS on a Raspberry Pi 3. It was also used for the FreeNAS box, which was ideal because FreeNAS only needs a screen briefly for setup.

Functionally speaking the portable external monitor has been working well. But the physical form factor left room for improvement: it wasn’t as portable as I would like.

The first part of the problem is weight: PEMv2 was built by stacking sheets of acrylic that had holes cut out to make room for components. There’s no fundamental reason why this subtractive construction technique had to be heavy. But in practice, holes were cut only when needed to make room. The result is a lot of excess acrylic. Acrylic is not super heavy, but it all adds up to just over 8 pounds which is ridiculously overweight for a 15″ screen.

The second part of the problem is size: PEMv2 was intended to fit within the width and height of my JanSport backpack. When assembled, I had a facepalm moment: it does not actually fit into the backpack because PEMv2 is rectangular and the backpack is not. The top of the backpack is rounded, with no room for PEMv2 top corners.

Lastly: while PEMv2 was thick enough to stand upright on its edge, it is easily tipped over and the upright vertical screen angle is not very ergonomic. We can definitely do better.

PEMv3 will try to address all of the above issues. To minimize physical volume, we’ll need a more compact way to package all the components. We’ll need to build our enclosure using less acrylic to further reduce weight. And we’d like to have an integrated stand that can securely prop up the screen at a better viewing angle

My Luggable PC display was a LCD panel I had salvaged from an old laptop, which I’m doing again for this external monitor project. When I pulled the Luggable PC panel out of the old laptop, I left most of the associated mounting hardware behind. During the Luggable PC project I wished I had also preserved the old mounting hardware.

The first reason is dimension data. When I mounted the screen to my Luggable PC, I had to measure the panel and design my frame to match. A Dell engineer did this work years ago, and when I threw away the mounting hardware, I threw that away as well.

The second reason is strength. A LCD panel is fragile, but when backed with its sheet metal frame, it becomes quite a bit stronger. This is usually a worthwhile trade off against the increased size and weight.

The third reason, less obvious than the previous two, is to manage heat. The back light assembly across the bottom of the screen would get quite hot when the panel is just sitting by itself. However, when the panel is mounted in its frame, the frame served a secondary purpose as heat sink.

The metal frame I want to reuse is attached to the plastic outer cover of the laptop lid. The attachment is done via small plastic rivets: bits of the plastic lid cover melted into the metal frame. Pulling off the frame with brute force is likely to bend and damage the frame, so the assembly is put under the drill press. After cores of all of the plastic rivets were drilled out (above), the metal frame easily pops off the plastic lid cover (below).

The metal frame can now be used to build the rest of the enclosure. The frame can be cut, drilled, and generally manipulated in ways that I would never do to the LCD panel itself. And when I’m done with all the prep work, the panel itself will drop right in to the frame. This should be much easier than what I had to do for the Luggable PC screen.