Neil's NES in a Cart Project

Ingredients: The Brains

First off, a really small Nintendo Entertainment System is required which can be rehoused inside the shell of the cart. Fortunately, there are many Famiclones to choose from, many of which contain a Nintendo on a single chip (NOAC) and therefore have really compact guts.

Here's the one I got. It's called an N-Joypad CD3900, has 59 games on 3 "Compact Disks" is very cheap and it's very widely available here in England. It has a PAL composite video and line audio outputs. Although dressed to (very loosely) resemble a Play Station, it is in reality a NES clone.

These are the game disks. They don't store any data, but rather select between different ROM images by virtue of their differing diameters. Once the lid of the machine is closed, the disk presses down on a number of the little buttons in the disk tray telling the NOAC which menu to load.

Here's the results of a trial gutting to check the size of the NOAC.

Not too shabby. The NES system is pretty much self contained on a small PCB. Those output connectors can be removed and that section of the PCB cut off to make it even smaller.

Two blobs of black epoxy are evident. The larger one is the ROM containing the 59 games and menu screens presumably. The smaller one is the NOAC itself. All the PCB traces from under the ROM blob have vias in their paths. I guess they might be there for in system programming at the factory (using a bed of nails in a jig). I wonder if that means I could replace that ROM with my own?

The remaining ICs and bunch of tiny transistors look like they have something to do with selecting between the menu screens. That's where the signals from the disc buttons seem to end up anyway.

Lastly, the ICs are powered directly by the system's four AA cells. There's no voltage regulator evident, so I'll probably need to provide one as I'll be using some other source for power.

New Housing

Ebay is a great place to find old hardware. I'm always a bit reluctant to destroy stuff which might be collectable one day, but for that genuine look I have to sacrifice a real Nintendo Game Pak. So might as well butcher one with few redeeming qualities...

Home Alone 2, variously described as being an awful release for the NES, seemed a good candidate. And is was very cheap.

Getting Nintendo's little security screws out can be a bit of a chore if you don't own a special little box spanner to fit them, but I find applying a bit of heat with a soldering iron loosens the little buggers enough to tease them out with long nose pliers.

Display

A built in display would look good and mean that I don't have to have a TV handy when I want to play. It would be nice if it fit where the label goes as the Game Pak already has the recess there and the shiny plastic under the label will look a bit out of place once I have removed the evil-looking infant's face from it.

A 3" LCD should fit nicely. It has to be able to accept a composite video feed however, which rules out readily available replacement displays such as for a Nintendo DS.

The DS screens look like they require some pretty fancy power rails, which would also make them a pain to use.

I had considered a OneStation but the screens look a bit too small, and besides where's the fun in throwing one of those into a new case?

After a bit of searching I found a source of new Samsung Camcorder LCD pods which come with all the electronics to display a PAL signal and light the backlight. There were a few to choose from but I settled on a 3 inch unit from a Samsung VP-L90.

This screen arrived from Latvia impressively quickly. It turns out to be a very well made unit. Almost seems like a waste to marry it to a crappy NOAC board.

The plastic shell come off after removing a few small screws. Inside, there is an assembly of a Casio LCD panel and control PCB On the latter there is a Sony colour decoder IC, a Casio ASIC for driving the panel and power supples for the circutry and the CCFL backlight. All the signals and power are transmitted to the unit via a long flexible PCB.

The overall thickness of the assembly might cause a headache. It's almost exactly the same as the outside dimension of the Game Pak. I'll probably have to mill the inside of the case pretty thin and maybe do something about that metal can over the backlight inverter to squeeze it in. Anyhow, I'll worry about that after checking everything works so far.

Initial Test

Ok, so here's my first trial run. Everything's being powered from a 5V bench supply derived from an old PC AT PSU. The NOAC is perfectly happy at 5V, and the inverter on the LCD board seems fine too at this voltage. The rest of the LCD circuitry requires a 3V supply as well as 5V. I rats nested a LM317 voltage regulator to provide this 3V from the 5V rail shared by everything else.

In the photo above the N-Joypad (now back together again for now!) is on the left, producing a composite video output to the yellow phono plug. I tacked a 10µF capacitor onto this plug to decouple the video signal. The LCD seems to prefer having that cap there for some reason. Also in the middle is the LM317 voltage regulator.

On the right is the disassembled LCD. I lightly tacked thin wires directly to the gold contacts on the end of the flexi ribbon to make the connections to it.

As can be seen there are a few issues with the picture: It's very bright, there's not much contrast and the colours are pretty random.

LCD Tweaks

It seems there is a multi channel DAC onboard the LCD board which sets the levels for things like brightness, contrast and tint. This IC (a MB88346) has a very simple serial interface, which I thought I should try and play with.

To test it out, I simply connnected the pins for this serial interface to some pins in the parallel port of my PC and wrote a little program to wiggle those signals. (It's for a Linux PC and uses the "parport" module to gain easy access to the PC parallel port.)

Here's the result so far. It seems the gamma channel has the most effect and needs to be set within quite a narrow range to get the best picture. In this photo, the IDC cable from my parallel port is visible next to the LCD. I included some 680 ohm resistors in the signal paths to afford my PC a little bit of protection in case something goes wrong.

I'll probably need to add a PIC micro or something like it to generate the initialisation sequence. Controls to adjust the brightness and contrast might be a good idea too.

Initial assembly

Making a space for the LCD by carefully removing the unused moulded pillars

This is my power source. It's an "emergency battery pack" intended to give a bit of extra life to a PSP. Inside is an 1800mAh li-ion cell and a neat little charger/dc-dc converter circuit. The output from the device is a regulated 5V, but it seems when the switch is moved to off, the input is directly connected through to the output. I will probably still need a low drop-out voltage regulator to keep the LCD and NOAC safe.

Here's roughly where the large components will go. I will remove the top strip from the NOAC PCB where the RCA sockets were mounted so the NOAC can sit neatly over the battery.

This is my makeshift rig for milling out a pocket to hold the LCD. With the driver PCB attached, the LCD module is 17.5mm thick at the widest point, versus the 17mm outer dimension of the Game Pak. I have thinned the plastic as much as I dare (to just under 1mm). The result is that the thinned parts are very soft, but with the LCD pressed against inside it should retain its overall rigidity.

I have also carefully cut the window for the display.

Controls

Next job is to work in the controls. I decided to use a real NES controller as opposed to the clumsy buttons supplied with the N-Joypad. This should look better when set into the original Game Pak.

I want a semi-flush look to the finished NES-in-a-cart, so to get this I need to thin down the original buttons to match the 2mm thickness of the Game Pak case. This also frees up some valuable space inside.

I also milled another little pocket to match the round back to the D-Pad. This is to help locate it and stop it sliding about too much. A couple of pillars are excised from the original controller and glued in place with epoxy. The section of PCB with the contacts for the D-Pad is cleanly cut off and screwed on. I will attach wires to the remains of the traces later.

Not too sure where the Start and Select buttons will go yet...