Tea Table

1987

Manchester University.

The student's union.

Fresher's week - beer - pizza.

In a dark and slightly pungent corner of the Solem bar, far from the scrum, two upright cabinets, one instantly forgettable, the other 'R-Type'. I can safely blame much of the last year's spare time on that game, but first a little personal history.

I grew up with computers. I remember the adverts that used to litter the back pages of Hobby Electronics and Electronics Today International, showing great praire-like motherboads stuffed with 14 pin DIL chips. Among these, the Microtan 79 and MK14 Sinclair offerings were just what a geeky 10 year-old wanted. Exactly, why I wanted them, I had no clear idea. But every holiday in Scarborough or Sheringham rekindled the idea that somehow the games (Space War, Pong) in the arcades were related to the slabs of fibreglass forested with quad CMOS NAND gates that I could buy for 'only' 100 quid or so. I'm not alone in having first met computers through gaming, but at the time owning a computer was a non-trivial step until Sir Clive's ZX81. Ah, when I were a lad...

"Time passes. A dwarf appears and throws a Z80 at you."

Anyway. Here we are. A quarter of a century later, and I and my wife are the proud owners of a MAME-based piece of furniture. It's name, 'tea-table', reflects the fact that it can actually do useful service as an occasional table, albeit one that lights up, makes noises, and has a higher SPEC-mark than the glowing Appley thing that I'm writing this on.

Rather than break down the construction into separate pages, I've put all the images and text into this one page. Most of the general details about building MAME-cabinets are covered well in 'Project Arcade' by John St. Clair, a useful book to read, and a fund of information about suppliers and so on. Where this project has departed from the usual run-of-the-mill is in its general layout (a table-like critter) and in its use of a TFT screen.

General

Well, on with the show. Tea-table had its main components built out of plywood, and I opted for two different thicknesses, using 12 and 16mm board as need arose. The joinery is pretty basic; I went for a screw-and-glue approach using 40mm countersunk woodscrews. You don't need to see a great photo of some sheets of plywood, so here's a noisy low-res image.

Tea Table comes in two parts, the lower box which contains the computer, and the upperbox which houses the screen. Both of these boxes have the same square 500mm x 500mm cross-section and are of differing depths - obviously, the PC-holding box is deeper than that for the screen. Here's a GIF of the cutting plan, to be used as a guide only.

Now, before you buy any lumber and start cutting it, I strongly recommend that you make some cardboard mock-ups of your provisional design. Not only will it give you a good idea about button positions and so on, but it will allow you to see and feel how different sizes and shapes work for the various parts of the unit.

My wife and I spent a fair bit of time wrestling with the conceptual skeleton of TT, trying to work out exactly how the screen would hinge and whether a rotating screen was desirable or feasible. In the end we went for a fixed screen in a traditional 4:3 landscape aspect. Oh, this blather all naturally assumes that you've taken the plunge and bought a flat screen monitor with the sole goal of gutting it for the display unit.

:|

I chose a low-power motherboard and CPU, deliberately. Our design means that ventilation is somewhat less than you might have in an upright cabinet and so I found a micro-ATX board from Asrock (K7S41) with an AMD 2800 mobile processor. We've given it 512 Mb of DDRAM, which clocks along at 333 MHz. This motherboard and the accompanying DVD drive (LG, single layer) and hard drive (40 Gb IDE, Western Digital) is powered from a fairly standard ATX PSU. Note, for both the motherboard and PSU I've chosen to mount the PCBs on sheets of thick polycarbonate plastic. This looks a little nicer and means that I can handle the boards a little more easily, without worrying about shocks or ESD.

We decided to put a CD-ROM drive in there so that we install drivers and whatnot more easily. It's an LG DVD ROM, so we could even use Tea Table as a DVD playback device if the mood were to take us. Now, if I'm running a Molex lead and an IDE cable to the CDROM, it makes sense to also have the hard disk somewhere nearby so that the cables can be bundled somewhat. So a pair of aluminium brackets were made that ensure that the drives stand apart from each other and also have a good size gap under them to improve air flow.

You'll see that for the above test we had a stock keyboard and mouse, and those are the last thing that we want for driving a MAME box. You want joysticks. And buttons. Lots of buttons. The best way to get an idea of where you want your controls is to go to an arcade, blow some cash and *play* various games with different arrangements; spot what you like and make a note of it. Once you've an idea of what works for your handsize and preferred game type, then lash together a mock-up using a cardboard box and some button/stick types. I opted for microswitches rather than leafsprings (the debates are legion) and bought a pair of Happ 360 optical sticks and also a pair of 8-way microswitch sticks for comparison.

However, these don't just plug into a USB or serial port. I bought the rather fine I-PAC/4 from Ultimarc, and this board plugs into a serial socket and allows a gloriously large number of switches to be interrogated.

Each of these plastic sheets is mounted to the plywood by protruding studding that has been epoxied into the wood. In case I needed to replace an item, I didn't want to be fiddling underneath the lower box with a screwdriver to undo a fastener. This means that every item mounted to the woodwork has had a hole sunk into it, into which a heavily epoxied set screw is fixed. As below.

Ah. Yes, air flow. Well, Tea Table isn't a terribly powerful beast, but we do want it to work without straining itself. The power supply (generic) was uncased, and I've tried to optimize the air flow around those components that need it most. Air exits the lower box through a single blown hole at the rear, and enters the box through two side-panels. Two rectangular holes in the lower box were cut, with recessed borders to allow pieces of aluminium mesh to be sunk and epoxied into place.

Other holes are cut for the power socket (a standard IEC connector) and switch, the main fan, the front socket panel and the speaker grilles.

On the inside, all wooden pieces are painted with flat grey primer. The bottom box, which holds the motherboard and PSU, and the top-box which holds the screen, all were then sprayed with nickel screening spray to act as an RFI screen. Over this RFI screen I've put a clear layer of varnish, and an electrical connection is made between the main power supply earth terminal, the RFI screening of the bottom-box, and the lid. This connection is achieved by a scrap of copper plate and an old hacksaw blade; essentially acting as a spring-loaded connection between the lid and bottom-box.

Control boxes

The boxes are made from the same brand of plywood used for the main boxes, but opting for thinner pieces to reduce the weight of the boxes. Each box is designed so that the upper surface will slope at a gentle angle, as you can see in this image.

Each box has a pair of side holes for buttons, and carries four aluminium tapped pillars in the corners, to accept the fasteners that hold on the top-plate. Each pillar is epoxied in place with high-strength epoxy (none of this 'rapid' stuff please - there's a trade-off between strength and speed of cure).

With the top plate off, you can see how tight these particular dimensions were - the joystick shaft protruded just enough for me to have to scoop out a depression in the control box's base so that the sticks motion wouldn't be impeded. Note also a few epoxied-in studs to hold the terminal blocks for the cabling.

Right. The top-plate. I opted for sheet aluminium for that, and took a little while chain-drilling holes to get the desired layout. You can use plywood if you like (makes for a chunkier box), or plastic, but I favoured toughened aluminium 1.5mm plate (nope, no idea of the grade).

Then, the surface was scoured with abrasive paper, and brought to a uniform sheen with metal wadding polish and a few minutes with an orbital sander converted into a cotton-rag polisher. The finished result is rather nice.

With luck you'll find a sensible way of drilling the holes in each corner of the top-plate corner so that they line up with the mounting pillars. I didn't. Counter-sunk holes in the top-plate mean that hands won't catch on fasteners when gaming. In the next image the top-plate has been drilled for its support columns and had its corners radiused.

Ah, I hear you say (humour me...) surely primer isn't going to be the final cosmetic effect? True. It isn't. Tea Table has a black and silver theme and so the control boxes share that motif. I used high gloss oil paint on the control boxes and applied it with a foam roller. I learned (fast!) that I should use many thin coats, each one ideally sanded down lightly to provide a key for the next layer. The fun didn't stop there though as the rather mottled result wasn't exactly what I wanted so then the paint was polished flat (!) with abrasive paste (T-Cut-like stuff called Commandant) and then buffed. The resulting finish would make Hotblack Desiato proud.

For connecting the control boxes to the main unit, I opted to use shielded multi-core cable. I dithered for a week or so if some kind of radio link wouldn't be a better idea, and toyed with building my own serial encoder, and feeding the output of that into the transmitter of a little RxTx transceiver. But sense got the better of me. For starters, a wire link is a darned sight easier to debug, and although less robust, I had to wonder how much grief Tea Table and its connectors would see. The control boxes I've built have seven pushbuttons and a single joystick. In total, that makes one common rail and eleven signal lines. Shielded cable is a little chunkier than unshielded, but any reduction in RFI is worth half a mm of diameter. As for the connectors, each control box cable ends in a high density 'D' shell plug. These are generally seen as VGA connectors on computer monitors and they give 15 pins in the footprint of a standard-pitch 9-pin 'D' shell connector.

Connections to these control boxes are made via D-shell connectors bolted to an aluminium plate that fixes to the front face of the lower box. This plate also carries the volume control knob (take a second hand set of amplified PC speakers and just rag 'em open) and a USB socket for handy connections to keyboards and mice.

Screen

Take heart, you're going to spend fewer Euro/dollars per screen mm^2 than we did. We can justify it because we're both silly. We chose a 19 inch screen from Novatech of Southampton and had no problems with dead or stuck pixels. It isn't a great screen, and I suspect it's a 6bit colour depth but we'll be playing pretty ropey games on it so that's not a problem. It has a single analogue input and is powered from a 9V DC PSU. The first thing to do is (of course) rag open the monitor's case and remove the panel. Naturally, you'll want the screen controls to be get-at-able, and so extract whatever push-button PCBs you find as well. We wanted the screen controls to be get-at-able and so we made up a remote board for the screen controls.

For the true otaku-jin, you can get very wrapped up in screen contrast and refresh speed specifications. However, trial sessions with the monitor on my wife's PC showed a very acceptable image and the choice of a cheap/cheerful monitor was vindicated.

Now, this lovely TFT screen has to be protected from abuse by something. I've chosen a large sheet of tinted plastic as a screen protector. There are two grades of acrylic; cast and extruded. Cast is a little more expensive than extruded, but has better optical properties and is no different in handling and cutting. I bought my screen plastic from Basmaplast of Weesp and got excellent serivce at a very good price. The piece I picked is 570 x 570 x 8 mm, in a 20% tint, and is shown here just as it came out of the cutting area.

I chose a tinted acrylic for a couple of reasons. Firstly, no matter how much I sweat over the TFT panel, it's still going to be visibly different from the rest of the innards of the top-box. So darkening the viewing screen will at least mute the sight of the guts of the top-box. Secondly, it looks cool. Note, it looks darker in this photo as the flash has to go through the sheet, be scattered from the paper, and then pass back through the sheet. In use, with the TFT panel providing the light, it won't look quite so dark.

To prevent bodily injury and so on, I've radiused the corners - pretty easy to do as acrylic is fairly forgiving as a plastic.

The screen protector is fixed to the upper box of the tea table by way of four pieces of aluminium angle-section. These are cut and filed so as to fit flush against the outer wall of the upper box as can be seen in this picture.

These aluminium pieces are bolted to the upper box by counter-sunk set-screws that fasten into captive nuts mounted on the inside of the top-box walls. All fasteners and so on were sourced from the good folk at Kruyt (ironmongers since 1890!) in Leiderdorp, and I've used stainless steel 20mm countersunk set-screws to fix the aluminium struts that lie under the screen protector.

Mechanisms

The whole point of this project is that not only can the object serve as a table, but it must be playable from a seated position - which means that the screen must be tiltable. So far you've seen the lower box which contains the computer itself and a little of the upper box which holds the screen. We now introduce the bits that join the two together. I chose to use stainless steel for the structure of the legs, and used a square section tube of around 20 x 20 mm and a wall thickness of 1.5 mm or so. Two lengths of this tubing were bent gently to give radius of curvatures of about 35 cm, with judicious use of heat (hint, two blowtorches - minimum and go easy on the pushing and work it when yellow-red hot, you don't want to lock stresses into the steel). These two uprights attach to a pair of legs that fix to the inner base of the lower box. The joint that links the upright to these inner legs is pretty important, the way in which the upper box hinges means that the uprights holding the upper box are offset somewhat, so the joint at the base of the uprights needs to be strong. I chose to braze all of the stainless steel parts used in Tea Table, and I've picked a fairly low melting temperature spelter for the non-load bearing parts. For this joint I used a 900 deg C spelter, and had plenty of contact area between the upright and the horizontal leg.

Here's the horizontal leg, this bolts into the lower box.

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Odds and sods from W.P. Hartwijk & Zn BV (Nieuw Beestenmarkt 7-11, 3212 CG, 0031 71 512 6627) Kruyt Leiderdrp http://www.kruytbv.nl/ Nieuwhuizenweg 19 Postbus 390 2314 XP Leiden Nederland Tel: 071-5899203 Fax: 071-5410200