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VULCAN-74 RETRO GAME COMPUTER

A POWERFUL RETRO GAME COMPUTER BUILT USING ONLY 1980'S LOGIC AND A SINGLE 6502 CPU.


Cat-5 wiring pairs

Peeling back the shielding to expose the individual wires.

After cutting the shield, give it a pull with the cutters to rip a section open to reveal the wires inside. You can now grab the wires and free them from the shielding. If you are cutting a length of more than 6 inches, it may be necessary to grab hold of the ends of the wire with plyers in order to leverage them out of the shield. Some brands of CAT-5 are more tightly bound than others.

If you can’t seem to get the wires to pull free on a longer length, then just cut away more of the shield using the wire cutters. Lengths of more than 12 inches usually require a good grip and decent amount of pull to free the wires.

Separate cat-5 wiring pairs

The four different pairs remove from the shield.

Once you free the wires from the shield, you will have eight individual wires configure as four twisted pairs. Each pair of wires will have a solid color and a white wire with matching color strips. The standard colors are Red, Green, Blue and Brown.

One thing I have noticed with these twisted pairs is that the orange and brown pairs are less twisted than the blue and green pairs. This seems to be the case even across various brands of wire, and I have yet to find an explanation as to why. Perhaps someone out there can enlighten me on this?

Untwisting wiring pairs

Untwisting the pairs of wires.

After you cut and remove all of the wires from the shield, it is time to untwist the wiring pairs. I find it more efficient to work on one operation at a time, so I always cut as many wires of the same length as required and then remove them all from the shielding.

Untwisting the wires is easy once you get the flow. Hold the wires loosely between your thumb and forefinger, and then “screw” them towards your hand so that the wires untwist. It only takes a few seconds to completely untwist a 12 inch length of wire this way. If your pairs are like mine, then the brown and orange will untwist with much less effort since they are less twisted than the other pairs.

Making the wire straight

Straightening the untwisted wires.

The untwisted wires will still have waves in it from its previous life as a twisted pair, and these need to be removed so that you can use them in your breadboard designs. You can just drag the wires through your grip to iron out the waves, but this can get hard on the fingers if you are straightening several hundred wires at a time.

A quick and painless way to straighten a lot of wire is to drag it past a round surface such as a pen or screwdriver shank. Place the wire so it partially wraps around the round body and then drag its full length along the surface with your thumb pressing it down. Depending on the wire, it may take more than one drag, but the wire will be pulled straight.

Removing the wire sheild

Removing the shield to expose the bare copper.

You now need to remove approximately one quarter inch of the wiring shield in order to insert the bare copper into your breadboard sockets and make a good contact. You can use a conventional wire stripping tool or just roll the wire over the edge of a slightly dull blade as shown here.

I find the blade rolling technique to be a lot faster than using a plyer style wire stripper, especially when doing a few hundred wires at a time. A few hundred?! Yeah, this kind of work uses thousands of wires, so every millisecond counts when you need that many. Using the knife, I can do a wire every 2 seconds easily. To avoid cutting my thumb from repeat cutting, I made the blade dull with a bit of emery cloth. It can easily cut the wire shield as I roll it along the blade edge, but does not cut my skin.

Bare copper for breadboard

Stripped wire ready for breadboard use.

The stripped wire shown here has the optimal amount of bare copper exposed for breadboard use, which is one quarter of an inch. If you expose less copper then your wire may not seat all the way into the metal contact inside the breadboard. If you expose too much copper though, the wire may push below the depth of your breadboard and make contact with the base below.

On a quality breadboard, there is a floor that will prevent the wire from pushing too far into the socket, but cheap boards do not have this, so try to keep the exposed wire to the optimal length, which is about a quarter inch, or slightly less than the total thickness of the breadboards plastic body.

Wire inserted to breadboard

A wire pushed into the breadboard tie point.

Because the wire shield is thicker than the exposed copper, it will hit the edge of the hole to seat your wire to the perfect depth, as long as the exposed copper is not too short or too long. Having your wires stripped to the correct depth makes it much easier to use them without having to worry about the proper seating. If you see any copper sticking out of the board, then you know the wire is not pushed in far enough. Wires can work their way out over time as you mess around on the board.

Multiple wires for GND and VCC

Cutting many small green wires for GND.

Ok, so that’s how I prepare my thousands of wires for breadboard use, now back to the project. The 24 individual breadboard panels mounted to each large panel need to be electrically connected so that they all share both ground (GND) and power (VCC) rails.

GND and VCC rails are the smaller strips placed at the top and bottom of each board that run horizontally instead of vertically. Since every IC requires one or more connections both to GND and VCC, it makes sense to have these busses available everywhere on the entire board. For both GND and VCC wires, I cut wires just long enough to join all of the rails both horizontally and vertically as well.

Decoupling capacitors

Adding decoupling capacitors.

Decoupling capacitors are used in circuit board design to help minimize voltage fluctuations as well as noise from fast switching gates. On a breadboard, these may not even be necessary as the very design of the breadboard interconnects act like capacitors, but I add them anyhow. With so many logic gates all switching in unison, there will be power fluctuations and high frequency spikes generated, so it is better to play it safe.

In previous breadboard designs that generated VGA or NTSC video, the decoupling capacitors did make a noticeable difference on the quality of the displayed video. Without the decoupling capacitors, there were faint horizontal patters displayed on the monitor, probably due to switching noise from the 32 74HC245 gates I had moving bus data around. Once I even had an AVR microcontroller refuse to boot without the caps, so I just add them as a habit now.

Joining VCC and GND rails

All VCC and GND rails tied together.

The VCC and GND rails are tied horizontally as well as vertically to minimize ground bounce and ground loops that could cause erratic behavior when many IC switch at the same time, drawing excessive current. In this design, I am using all CMOS type ICs, which are much less hungry than the original TTL logic types that were first introduced in the early 1970’s.

Decoupling capacitors are placed in each corner of all 24 breadboards, the goal being a reduction in high frequency switching noise and quick power spikes. The value of the decoupling capacitors uses is .01uF (microfarads), so the marking on the face will be 104. The large breadboard is now ready for use, with all power and ground rails tied together.






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