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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.


Adding joystick ports

Atari / Commodore compatible joystick ports.

Vulcan-74 will be a powerful game computer as well as a fully functional computer, so it will require a multitude of user ports such as keyboard, joysticks, audio, video, and some kind of external storage such as a solid state drive or cartridge. Although I have not yet fully defined the types of IO devices to be used, there are some that are required.

Shown here is one of the two 9 pin Atari / Commodore compatible joystick ports, which will allow all of the standard game controllers used from the 70’s to the 90’s to work on my system. These joysticks are very simple, as they are nothing more than contact switches, so reading them can be achieved by placing a buffer like a 74HC245 right onto the data bus for each joystick port.

Hand filing out the half inch thick aluminum took a bit of effort though! I started by drilling two holes as close to the edges as possible and then did the rest with a tiny round file. No part of this project is going to be easy… I accept that.

The World's Largest Breadboard!

The MOAB… World’s Largest Breadboard?

I have no idea if this is the World’s largest Breadboard, but if it’s not, I sure would like to see one larger! The MOAB has almost 40,000 tie points, and takes up most of an 8 foot long table, leaving just enough room for my trusty Commodore 1702 monitor. Speaking of World Records, I am actually lucky enough to have one hanging on my wall, and had my mug shown in the hard cover book…

https://www.atomiczombie.com/tutorial-world-record-skycycle

Sometimes hard core electronics nerds need a bit of danger too! Anyhow, back on topic. I am looking forward to filling up both of these massive boards with hundreds of logic chips and thousands of wires as Vulcan-74 takes form as the most powerful 1980’s game computer ever created!

Logic chips in cabinets

This project needs chips, lotsa chips.

Luckily, I have hundreds of drawers full of 74HC logic gates to choose from. Although I may only need perhaps 10 different ICs altogether, I will need hundreds of them. The 74HC245 buffer for instance is will be well used in a project like this for banks switching between different SRAMs and bus paths. I usually purchase IC is quantities of 32 or more since there is a price break, so I am well stocked.

The interesting thing about these 74HC logic ICs is that they are still mass produced today, and are available in breadboard friendly DIP format. Back in 1980, HC logic was a fairly new to the industry, which was dominated by the older TTL standard.  HC requires much less power than TTL, and can run about twice as fast, which is why it later became the more accepted standard. Even the 6502 CPU, which is still manufactured by the original distribution company “Wester Design Center”, is also CMOS, so it will be completely compatible with all of my 74HC logic.

IC pins too wide

A new IC has a stance too large for a breadboard.

DIP ICs are manufactured to be placed into a circuit board by a machine, so the legs are often splayed outwards in a way that makes them too wide for the standard .1” spacing of the breadboard sockets. The pitch between the pins is always ok, but the width is typically one row out of alignment as shown here. Some adjustment needs to be made to allow proper insertion of the IC.

Bending IC pins

Rolling the IC to adjust the pin spacing.

To allow the IC to be pressed into the breadboard properly, the rows of legs will need to be bent slightly inwards to match the .1” standard spacing. The robots that pick and place ICs in mass production do this automatically, but unfortunately, I lack a production line in my nerd cave! No problem, there is an easy fix.

Grab the IC by the ends as shown here, and just roll it towards the pins as you press it against a totally flat surface such as a desk. After a few tries, you will know exactly how much bend to put on the legs, and how much force it requires. If you over bend the legs a bit, they can be easily adjusted back the other way as well.

I actually remember seeing a plyer like tool that did this job as well, but I have no idea what it was called or if it would still be available. This is a surface mount world now, and I am living in the past.

IC legs fit into breadboard

The adjusted IC fits the breadboard perfectly.

Here you can see how a DIP should fit into a breadboard. The pins will align perfectly with the spacing of the holes in the breadboard, allowing you to press straight down to seat the chip. If the pins are out of alignment, they could be bent if they do not seat into the hole when you are pressing down. One quick press with your thumb and the IC should just snap right down.

IC body too wide

Longer IC packages waste breadboard space.

Another breadboard annoyance can happen when the IC manufacturer extends the body beyond the first and last leg so that you have to waste one vertical column of holes between each IC. This is especially annoying if you wanted something like six 245 buffers on one panel as shown above, since you end up just 2 holes short thanks to the 5 wasted holes.

This problem seems to be random, even with the same manufacturer. I have two different sizes of NXP 245 buffers that actually have the same part number. One wastes a row and the other does not. All is not lost though, as I have found a way to beat this problem with a little hacking (literally).

Dremel with sanding drum

A Dremel tool with a sanding drum.

When I called this a hack, I wasn’t kidding because the job involves hacking the offending section of the IC body away with a sanding or grinding bit. The actual integrated circuit is a tiny wafer placed in the center of the IC package, connected to the legs by tiny wires, so there is no risk of removing anything useful by grinding away some of the overhanging package.

Any high speed tool that includes a sanding or grinding disc will do the job. I have even used bench tools such as a belt sander and vertical grinder to do this hack job. There will be fine dust, so either use a mask or do what I do… hold your breath!

Grinding down IC body

Sanding away the IC body overhang.

Hold the IC by the body and press it lightly into the sanding drum or disc, moving back and forth to take off the excess material evenly. Take off only as much material as necessary so that the ICs will sit next to each other on the breadboard without touching. Avoid sanding or grinding all the way to the metal leg, as that would me more material than necessary.

Once you get the first pair of ICs shaved down to fit, it will be easy to do the same to the others.

Compacted IC on breadboard

Six ICs living side by side with space to spare.

Now that the IC bodies have been shaved down to a more usable length, all six buffers fit into a breadboard row and there are 3 holes to spare. A large project like Vulcan-74 may use 48 or more of these 74HC245 buffers to switch all of the various data paths, so this chip shaving operation saves massive amounts of board space.






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