Building a Digital Battlemat

I'm a geek, that's pretty obvious. But, I'm a geek in more than one way... not only do I admin computer systems all day long and write software in my spare time... but I play RPGs too. Yes, the computer-based kind, but in this case I'm talking about the "old school" table top variety. D&D in particular.

The trouble I've always had with table top RGPs is the whole visual interface to the game. The dry-erase battle mats, graph paper squares, and cardboard tiles of yesteryear simply don't do justice to modern game maps. True, some of the most classic modules in gaming history (Temple of Elemental Evil, anyone?) came with maps that were hand drawn on graph paper. These days, however, top-notch artwork has a serious role in modern gaming, especially those beautifully crafted maps. Yet, publishers continue to take the time to commission, render, print, and sell (either separately or as part of a module) a beautiful top-down scale view of a dungeon environment while knowing only person that will ever get to see it is the game master.

Recently, game mapping, cartography, and display technologies have gotten better and better. Software like Campaign Cartographer and Dundjinni make creating beautiful game maps easier than ever, and tools like Battlegrounds, FantasyGrounds, MapTool, and ScreenMonkey promise to serve them up to players. But only take aim at the VTT market, leaving old school table-top gamers in the dust. Yet a number of pioneering hardware hackers and game enthusiasts have taken a stab at solving "the table top map problem." Some gamers use a large computer monitor or television to display their maps. That's an easy solution, but not one I favor because the image is not horizontal, and therefore you can't use miniatures. Using a projector is another solution that is starting to become popular. Apart from just pointing it at a wall, you can use one for a real horizontal display by mounting it on the ceiling and aiming down. Voila, instant high-quality battle map! The problem is that projectors are expensive, and the rigs are not portable.

My first thought for a personal solution to "the table top map problem" was, in fact, to build my own projector (heck, I did it for my home theater). I'd save a fortune, but portability would still be an issue. Still, I got myself pretty enamoured with the idea before a good friend of mine suggested an easier solution (which he himself is planning using for one of his own projects): just use a large LCD screen and lay it flat on the table. Now, most LCDs won't just lay down flat on a table top, so I knew I'd have to build a box around it, but I quickly realized that doing so isn't a complicated build at all. An LCD used in this way would produce the same quality as a projection rig, but be no more complex than using a vertical screen. An LCD would also be portable, underlit (instead of overlit; no shadows cast by figures placed upon it), brighter (no need to play in the dark), and easier to build (only a bit harder than a picture frame). On the down side an LCD is of a fixed size, and it would end up being smaller than a projected image. Still though, for the advantages offered, I knew I at least had to try.

This article discusses a "proof of concept" assembly of a "Digital Battle Mat," built from a flat screen computer LCD monitor. The idea is to repackage the display element and control circuitry into what is essentially a glorified picture frame. My goal is to produce a high quality, horizontal (face up), computer controlled battle mat that can be using for table top gaming.

Selecting a Monitor

The first step of this build was deciding which monitor to use. I knew that I wanted to use a a 22" LCD because I felt that they represent a good balance of: 1) size, 2) portability, and 3) cost effectiveness. A 22" diagonal, 16:9 wide screen LCD gives you a display area of about 11"x19". That's not huge, but it's enough to display most rooms in a typical dungeon (up to a 55'x95' room in standard 5' scale). With a resolution of 1680x1050, I can comfortably drive the display with my laptop's external monitor connection. It weighs about 12 lbs, and brand new models can be had for less than $200 if you're a diligent shopper, and used models may go for a lot less. The next size monitor up from 22" is 24". While they offer a little more realestate (~ 12"x21"), they also cost considerably more (new models start near $350) because they support a higher resolution and can be used as a 1080p capable HD TV. The bottom line is that for this rig, a 22" monitor is probably the best bang for the buck.

I purchased my LCD used from eBay and paid very little for it. In fact, I'm ashamed to admit how little it cost me. It's an AOC G22LWK with a black chassis. For an "off-brand" monitor, it's got an impressive array of features for the price point: a 700:1 contrast ratio, VGA and DVI-D inputs, built in speakers, etc.

A little fuzzy here, but quite sharp in person.

Backplate Removal

After verifying that the monitor actually worked (hey, it was used), it was time to get right work and disassemble the panel. I don't actually like using the word "stripping," because I didn't want to take apart of the LCD itself... there's no need to do backlight or anti-glare removal like there would be when building a projector. There are a lot of guides available on how to fully strip an LCD if you need, but in my case, I'm really just taking the chassis away. To do so, I placed the monitor face down on a clean, soft, white towel (to avoid scratching it) and removed the hand full of screws which held it together. After that, the backplate lifted off.

Eight screws hold the backplate on the monitor.

With the screws removed, the back comes right off.

With the backplate removed, it's time to get rid of the stand. On this model, two heavy duty screws attach the stand to an extra metal plate, which is in turn fastened to the LCD housing and the front bezel.

The stand is firmly attached with a heavy duty mount.

But don't worry, because it all unscrews.

Disconnecting Stuff

Next, we have to detach the few components which mount directly to the bezel. This includes the button board and the speakers. Again, these all unscrew easily. In the case of the speakers, the cables also unharness with ease.

Speakers are mounted directly to the bezel.

So, they must be detached before we can disassemble further.

The same follows true for the button board.

Removing the Bezel

With the stand mount removed, and the speakers and button board detached from the bezel, it's now a simple matter to unscrew the LCD housing and lift it clear of the bezel. In this model, the whole unit comes away in one clean piece.

The LCD, along with the back light, control circuit, and power adapter all comes out clean.

Here's a better view of the button board, which is still attached.

Shield Removal

Next, I turned my attention to the big aluminum shield which protects the circuit boards that actually make the panel work. It's a big bulky thing that would just waste space in my design, so I set about removing it. In unscrewed from the LCD housing fairly easily, but there were also the cable screws on the VGA and DVI-D inputs to take out.

The posts into which you screw your video cable are themselves screws (nuts, actually).

But, like everything else, they come right out.

From here, that big piece of shielding comes right off giving us a nice clean look at the LCD's electronics. There are two circuit boards under here. One of them is the power adapter. You can recognize it easily by the large heat sink and big capacitors (not to mention the fact that this is where the power cable plug is. The other board is obviously the video driver and control board.

With the shield off, you can see the circuits that run the display.

High voltage, be careful.

Lots of wires make this part really pretty.

Cleaning Up

I'm almost done with the disassembly at this point. There are only a few things that I need to do, all to clean up the "bottom" edge of the LCD housing. It is important that all of the edges be flat so the unit fits snugly into its new case.

First up, the button board's cable is tunneled through the LCD housing. That in itself isn't a problem, but it juts out of the side of the housing in a way that might make the job of getting the whole thing to snug into a new case kind of difficult. So, we unplug the button board and remove it for now.

All of these wires will get in the way.

Unplug the button board.

Then carefully pull it free.

Now the speakers wires need to be "managed" a little bit so that they're out of the way. Luckily, this is pretty easy to do, as they can be coiled up a little tighter, and they're clear. While I'm at it, I also bent the part of the LCD housing which was previously a mounting tab out of the way.

The speaker wire's out of the way, but that tab will be trouble.

Fortunately, it's easy to bend.

And with that, the LCD unit is ready. It's a lot of photos, but all I've done is remove a few unnecessary bits and clean up the profile a bit. My LCD unit is now flat on five sides, and ready to go into its new enclosure.

Measuring the Box

Now that my LCD is stripped and ready to go, it's time to turn my attention to the enclosure assembly. As I mentioned before, my ultimate goal is to "repackage" the LCD into a new home... basically a glorified picture frame that can sit flat on a table. The new enclosure, made of wood, should be prettier and more sturdy than the original plastic monitor housing. A protective layer of plexiglass will sit on top of the LCD as a scratch shield (it can always be replaced if necessary). It won't even have a lip on top.

Since measuring and cutting wood is boring, I'll skip documenting too much about that part. Suffice it to say, a little time alone with my LCD and a ruler told me the following:

None of that probably means much to you yet, but anway, I cut the pieces I need for my enclosure. I used 1/2" premium red oak boards (from my local hardware mega-store) which I've cut to a height of 2 3/4" and lengths sufficient to enclose my LCD (with 45 degree mitered corners). I also assembled the first three sides with the help of some 90 degree framing clams, a little wood glue, and some finishing nails. I've also cut the backpiece, which is made of 1/4" MDF, and (unpictured) the plexiglass top.

All of the (wood) pieces of my new enclosure.

This is how they'll all fit together.

With the backpiece in place, it's just missing the LCD!

Inserting the LCD

Inserting the LCD is now a simple matter. If I measured and cut everything properly, it will fit quite snugly. Please note that the following pictures show the same LCD unit photographed earlier, it has just been turned over now.

These are the

The LCD element goes in quite easily using its

Success, it fits!

This is, roughly, what it will look like when complete.

Cutting Inputs

Highly encouraged by how well my enclosure fit, I concluded that I was good to press on. Before sealing up the box, it is necessary to do a little bit of cutting. After all, the video cable and power cord have to plug into something, right? Also, it would be a shame to waste those speakers.

Some quick measurements and a few pencil markings later, I had the outlines for what I would need to cut and drill.

It's hard to see, but I've allocated room for both speakers, the button board, and all the inputs for video, audio, and power.

The big problem with cutting inputs has to do with precision. In particular, the video and power inputs have to be very exact sizes if you want them to look any good (and if you want the cables to fit and connect properly on both sides). Since I don't have access to a CNC machine to do the cutting for me, I decided to improvise and use what I already had - the same input holes the monitor used. After all, Jeff Smith taught me to be frugal in the 80's, and I still continue to do my best.

The aluminum shield I removed already has perfectly machined input holes already cut!

A few minutes with a good pair of tin-snips, and they're reusable.

If you happen to want to do this yourself, remember to be very careful with your tin-snips. They'll produce sharp edges and very pointy little slivers of metal. It's also very easy to bend your shielding, and if you do so like I did, you'll need to carefully press out the bends and get your "plate" flat again. You'll also notice that (for now) I have avoided trimming them down too far. I knew I didn't want all of the extra holes to be visible when I use these pieces, so that's where I cut. Since I'm not yet thinking about final appearance, I want to leave as much "work room" as possible.

With issue of masking the input hole solved, I was able to move on to taking the measurements for the hole I'd actually have to cut. The idea is to make the hole just large enough for the cable to pass through, yet still have it be small enough for the metal plate to cover it up and look nice. After looking at my VGA cable (in my case, a standard 12" VGA cable with the shroud removed from one end), power-input module, and audio jack, I was easily able to make the tracings I needed.

A VGA extension cable with the plastic shroud broken off one end.

A two-piece, screw-together audio jack.

A standard IEC power entry module.

Now, routing a small square hole out of oak isn't an easy chore. I ended up using Rotozip Sabrecut bits in my Dremel, with its plunge-router attachment. Taking it slowly in a few passes, I was able to knock out the holes relatively easily. I also took the time to drill holes for my button board (more on how that will work on the next page), and for the speaker ports.

The hole for my VGA cable to pass through.

Mounting the Bottom Plate

Next up, it was time to install the "mounts" for the bottom plate. To do this, I simply cut some 1/2" x 1/2" x 2" blocks out of scrap wood. They're easily glued in at this point by mock assembling the box (with the bottom on), and setting them in place. After the glue had partially set, I flipped it over and clamped the blocks in place to cure.

These are the blocks that the bottom plate screws into.

Be sure to clamp while the glue is drying.

Speaking of the bottom plate, I figured that this would be a good time to cut holes for the ventilation. A normal LCD doesn't sport a fan, but then a normal LCD doesn't sit horizontally. For thermal security, I decided to go ahead and install a 60mm exhaust fan... just to be safe. I therefore cut two 2 1/4" holes (using a hole saw) in the backplate. One went directly above the large heat sink on the power converter circuit board. This will be the "intake," and is designed to draw fresh air directly over the component that needs the most cooling. Warm air will be forced out by the fan, for which I cut a second hole in a corner where there was room to put it.

Cool air comes in over the heat sink.

Warm air is blown out by the fan.


The next thing on my list may seem rather odd, but there's a method to my madness. I applied the first coat of stain at this point. More on that later, but the reason is pretty simple; I wanted to do as little manipulation as possible after the box was assembled. Knocking out one coat of stain now was an easy win.

After that, it was finally time to assemble the enclosure. First up, the LCD is re-inserted into the U formed by the first three sides. Then, the fourth side is glued, clamped, and finally nailed into place (gingerly! you want to be VERY careful nailing a box that contains your LCD!). Unfortunately, my sides didn't match up exactly. Apparently, my 45-degree angles weren't quite 45-degrees. It's a bit annoying, but nothing a little wood filler wasn't able to take care of.

The box (not yet glued together) with one coat of stain.

With the LCD inserted, the last side is attached.

Small gaps can be fixed with wood filler.

And that's that! The box is now assembled, and the only thing that remains is finishing it, and wiring up the electronics inside.

Staining and Varnishing

The first thing to do after the box has been assembled is to finish staining it. Now, I'd already done one coat, but there was a lot more to do. Before staining, it's important to "secure" the LCD to prevent damage. For me, that meant a few layers of paper over the top, followed by a layer of blue painter's tape. It's important to note that none of the tape's adhesive is in contact with the LCD's glass in these photos. The glass is covered by paper, the tape then covers the glass and the metal frame.

Staining is pretty easy work. I used Olympic brand oil-based "Red Oak" wood stain, available from my local home improvement mega-store. I didn't necessarily pick the red oak color because the wood I'm using actually is red oak, but because the color is nice. After the stain went on (this is the second coat), I applied three coats of Olympic satin-finish polyurethane varnish (all according to the manufacturer's instructions). Twenty four hours after the last coat of varnish, I had a beautiful silky-smooth wooden box wrapped around my LCD.

Applying the stain and varnish all looks the same.

Installing the Buttons

Now, we're pretty much in the home stretch. I decided to get the more complicated part out of the way first, and that meant installing the button bar. I'd already pre-drilled a series of holes in the enclosure which match up to the control buttons. A sixth hole was drilled for the power indicator. I've also trimmed, stained, and varnished a series of wooden pegs which will act as buttons. One technique I've seen for doing buttons in this was advocates pushing thumbtacks into the back of them (to prevent them from falling out). I decided to use small loops of 1/4" ID plastic tubing (the same diameter as the buttons themselves).

The buttons are then inserted from the rear, and the button bar is positioned over top of them, with a nylon spacer keeping the circuit board fixed in place. The buttons can now be activated from outside the box, and the resulting look matches the rest of the enclosure.

Small bits of tubing wrap around the base of these pegs.


And from the front, they all line up nicely.

Installing the Inputs

The three inputs, power, audio, and video, are up for installation next. I figured that doing them from hardest to easiest would be a good idea, so I decided to go with audio first. The audio jack I used was fairly simple to get into the case: it just screwed in to the hole I had drilled for it. The key was to use a drill bit that was only slightly smaller than the threads of the jack. Sure, it takes a little work to screw something into oak by hand, but it can be done. After that, it was time to solder the audio wires together.

Audio jack installed.

Audio jack soldered together.

Audio jack fully installed.

The next input to install is the power module. This one also requires a little bit of soldering, but it's a bit easier because it's less precise (the pieces are bigger and easier to reach).

The power module is tricky to get right, because it's important that polarity be observed. The Load-in lines must connect, as must the Neutral lines, and the Ground lines. Again, if you happen to be considering building an enclosure like this for yourself, please be very careful when working with electrical wiring. If you cross your wires, you can very well destroy your LCD and/or injure yourself.

On a more positive note, you can also see that I've hard-wired my fan directly into the input power. While I considered installing a switch for the fan, I decided that it wasn't really necessary.

Here's how the power module is wired up.

Lastly, it's time for the VGA input. The first thing I did was to pass the broken-up VGA cable through the hole I'd cut for it. The cable is then attached to the mask plate I cut for it using the bolt end of the hex nuts that are meant to secure the input cable. A couple of #4 nuts is all it takes. Next, the input plate itself (with the db15 cable attached) is then glued to the box itself. Yes, I said glued it. Glue is an easy, secure way to attach the two pieces in a way that looks good.

The cable is attached to the mask plate by the hex nuts.

A little glue is all it takes.

Here's the cable looped to the circuit board.