Flat panel light box

I’ve been getting into making stained glass pieces, as I’ve been taking a class at the Rochester Memorial Art Gallery.  One of the tools they have available there is a light box, which I have used to make the template for the macaw piece I’m making.  I used it to help me adapt a pattern I found online into something that better suits my needs.  I traced it, then retraced that sketch.

The light box also works well to see how things look with light behind them, however it’s not something I can use a lot for this, since my project is a couple dozen pieces of glass and we have to share the light box.


On the recycle pile at work was a couple of old, broken laptops.  I snagged two of them; one with an LED backlight, and one with a CCFT backlight.  I thought that the LED one would be easier to get working.


Over at Interlock, I tore apart the screens, tossing out the LCD panel, so I was left with just the light source, light guide, diffusion screens, and control circuitry.  Its control/driver board also managed the LCD itself.  There were many test points on the back, so I applied power to the “LED PWR” pin, ground to a ground point, then about +5 volts to the BLEN (assuming it to be “backlight enable”) as well as the “PWM” test point. After futzing with it for a little bit, I gave up and focused efforts on the CCFT-based one.

The slightly larger CCFT (Fluorescent) based one had a single board that connected to the backlight tube through standard white/pink silicone-insulated wiring.  The board itself had one tiny connector on one side with a few pins that seemed to have obvious use.  V+, which assumably powers the backlight circuitry, should be connected to +5 or maybe +12.  GND, which of course is ground. Then two other connections “EN” and “CTRL”, which I guessed to be “Enable” and “Control”.  A guess would be to tie these to a logic “high” which might maybe enable the thing.

I connected just the V+ and GND to a power supply, and applied power.  Ranging from 0v up through 12v yielded no results. I connected the other two logic lines to power too, and started ramping up the power.  At around 7v, the backlight flickered on, but then wouldn’t do anything until I brought the power back to 0v, and then back up again.

On a hunch, I figured that the backlight needs a higher voltage, and the logic stays at TTL levels.  Applying the same power to both would give a possible point between the two where both kinda worked, which is where I saw the flicker.  I hacked together two power supplies, with grounds tied together, 5v from one power brick, and the V+ to the variable supply.

I ramped up the voltage, and sure enough, it would get dim around 7v, then go full brightness around 12v.  It seemed to use about 300mA to drive it too. Good to know.  I found a 12v power brick and.. it would light for about 20 seconds then power itself off.  The 12v brick put out 18v.

I eventually found a brick that worked, so i hooked up two supplies, a 5v and a 12v and it was stable and bright.  Next would be the task to put in a 5v regulator to provide the 5v it needs, so i can run it all on one single power supply.

A simple circuit using a 7805 and two capacitors later, and I have 12v in, and a backlight lit!  I wrapped the circuit in tape (purple because it was there), hooked it up to a power connector, and reassembled the case.

Best of all, it all managed to fit within the old plastics. Huzzah!

Now I just need to put something on the diffusers to protect them from cut glass, maybe a piece of plexi, or even a large Ziplock or plastic wrap, and I’ll be set!

from on November 5th, 2014Comments1 Comment

JAMMA Video Game Test Rig Box

I decided to package up my JAMMA test rig so that I could demo Crazy Otto at Rochester BarCamp for today.  My design was basically a box that would house the entire thing, with a nice control panel for player 1.  As you can see in the above image, I have the A/V cable going to an external monitor.  Broken out on the box are player 1 and 2 start, coin 1, and player 1 controls – joystick and 3 buttons.  On the right side of the box are the three “coin box” controls — Test, Tilt, and Service, for testing those functions of the board.  Also on that side is a nice handle to help it be portable.

This is a continuation of part 1, where I updated the AV connections of the rig.

This is about the extent of blueprints I have for this.  I knew I needed 14″ depth for the monitor, and that it needed about a 2″ rise from the back to the front to put it at a good angle.  I wanted it to be 18″ wide, and 24″ deep.  That would give enough room for a game board inside of it, as well as for a decent sized control panel.

 I started by cutting a sheet of plywood I’ve had in our garage for a while.  I also built the control panel using spare parts I had.  Thanks to members of Interlock to help me use the table saw, suggest tools and offer bits of wood.  :D

Some standard microswitch buttons, and a nice ball-top leaf-switch joystick.

The basic construction is that I glued some cleats on the inside of each side. Then the back, bottom, front and control panel will be screwed to it.  After that, it looked like this:


I also cut and drilled a small metal bracket to hold the power supply in place, which you can see in the above.  The coin 1 button on the front has a 12v light in it.  The old P2 controller is still attached to the JAMMA rig, in case I want to test/play 2 player games.  You can also see the 1 1/4″ fine thread drywall screws holding it together here.  From here, the only change is that I painted it, stinking up our garage in the process. heh.  The top lid hooks under the control panel, and has a cleat in the back to keep it from sliding off the back.  There’s a single screw to hold it in place, and to let it be carried withot the contents falling out.

The great thing about this thing is that it’s easy to tote this thing around to play/demo games and such.  It takes two trips since the monitor is cumbersome, and the box itself is pretty heavy, but it’s SIGNIFICANTLY easier than toting around a full arcade cabinet.

For reference, here’s the JAMMA pinout standard:  (Most games since the late 1980s use this or a variant of it — for example, Neo Geo adds additional buttons on unused pins, Rampart uses a trackball on the joystick pins, and Mortal Kombat has additional buttons on another interface harness.)

The power and ground at the top portion are wired directly to the old PC power supply.  Coin counters and lockout coils are not wired to anything.  The speaker wires are broken out to a RCA plug, and the Video (RGB,Sync) are out to a DIN connector, as seen in the previous post.  Service, Tilt, and Test are wired to the three switches on the side of the box.  Coin switch 1, and the two start buttons are on the control panel, as are all of the 1P controls (on the right).

from on April 19th, 2014Comments0 Comments

Repairing the audio on a Pac-Man arcade board

I got this knockoff JAMMA Ms Pac-Man arcade board many years back.  It’s got two ROMs instead of the authentic board’s 6 (9 for Ms Pac), and is substantially smaller than the “real thing”.  The only issue is that the audio is poor… REALLY poor.  It makes sounds but they’re… wrong and noisy.

I took over some desk space at Interlock and got to work.  (I should note that the beverages you can see here are other people’s, not mine. ;)

I traced the audio circuit on a real Pac-Man schematic (seen on my laptop’s monitor), and buzzed it out on the Yenox board to try to corrolate the two.

I had to trace four similar paths from a quad flip-flop, through a quad bidirecional switch, to the audio output.  It got really confusing at times, and took me probably a bit longer than it should have.  For the most part, they were pin-for-pin correct as far as how they were wired.  These chips have the same device (eg, a flip flop, or a logic gate) repeated 4 or 6 times.  In some cases here, the Yenox board had a different one of these devices hooked up, which added to the confusion.

This portion of the circuit uses 8 resistors to make a digital-to-analog converter. These generally work by having different resistance levels, usually something like multiples of eachother, eg,  10k ohm, 22k ohm, 47k ohm then 100kohm.  I traced out all of the lines on the Yenox board and I found out that not only were the resistors in the wrong order on the board, but they were also wildly wrong (47 ohm instead of 4.7k ohm), which you can see in this table I made:


You can see these resistors here on the Yenox board, right next to the JAMMA connector.  They start from the left with R1 (my notation.)  The printing on the board completely matched the resistance values that sat on them, so it’s obvious that the engineer who made this board seriously screwed it up in the design stage.

I replaced resistors R3 – R7.  I put them in with the gold band closer to the JAMMA connector, rather than the other way around.

And now it sounds near-perfect.  There’s a little bit of popping left, but I was getting tired and decided to head home for the night.  I’ll hook it up to an oscilloscope at some point and see if i can figure out which line is causing problems.

For what it’s worth, I also did the same as this on the video path DAC, seen in the above picture as the next three groups of resistors.  In the above, the group of four and then the group of five are for audio, then the next group of three is for the “red”, next three for “green”, next two for “blue”, and the remaining two are for the sync.  Again, there were some 47 ohm resistors mixed in, and notice two of the three in the “green” section are identical (red-red-brown)… which is surely wrong.  Color is now perfect on the board too!

from on February 12th, 2014Comments0 Comments