Slicing And Dicing The Bits: CPU Design The Old Fashioned Way

April 22, 2024 by Al Williams 9 Comments

Writing for Hackaday can be somewhat hazardous. Sure, we don’t often have to hide from angry spies or corporate thugs. But we do often write about something and then want to buy it. Expensive? Hard to find? Not needed? Doesn’t really matter. My latest experience with this effect was due to a recent article I wrote about the AM2900 bitslice family of chips. Many vintage computers and video games have them inside, and, as I explained before, they are like a building block you use to build a CPU with the capabilities you need. I had read about these back in the 1970s but never had a chance to work with them.

As I was writing, I wondered if there was anything left for sale with these chips. Turns out you can still get the chips — most of them — pretty readily. But I also found an eBay listing for an AM2900 “learning and evaluation kit.” How many people would want such a thing? Apparently enough that I had to bid a fair bit of coin to take possession of it, but I did. The board looked like it was probably never used. It had the warranty card and all the paperwork. It looked in pristine condition. Powering it up, it seemed to work well.

What Is It?

The board hardly looks at least 40 years old.

The board is a bit larger than a letter-sized sheet of paper. Along the top, there are three banks of four LEDs. The bottom edge has three banks of switches. One bank has three switches, and the other two each have four switches. Two more switches control the board’s operation, and two momentary pushbutton switches.

The heart of the device, though, is the AM2901, a 4-bit “slice.” It isn’t quite a CPU but more just the ALU for a CPU. There’s also an AM2909, which controls the microcode memory. In addition, there’s a small amount of memory spread out over several chips.

A real computer would probably have many slices that work together. It would also have a lot more microprogram memory and then more memory to store the actual program. Microcode is a very simple program that knows how to execute instructions for the CPU. Continue reading “Slicing And Dicing The Bits: CPU Design The Old Fashioned Way” →

Manual Supports For 3D Printing

April 21, 2024 by Al Williams 12 Comments

[MakerSpace] wanted to 3D print an RFID card holder. On one side is a slot for a card and on the other side has recesses for the RFID antenna. They used these to control access to machines and were milling them out using a CNC machine. Since there were no flat surfaces, he had to turn on supports in the slicer, right? No. He does use supports, but not in the way you might imagine.

Inspired by creating cast iron using sand casting, he decided to first 3D print a reusable “core” using PETG. This core will support future prints that use PLA. When printing the actual item, the printer lays down the first few layers and pauses. This allows you to stick the core in and resume the print. After the print completes, you can remove the core, and the results look great, as you can see in the video below.

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Measuring An Unknown Velocity Factor

April 19, 2024 by Al Williams 14 Comments

When is the speed of light not the speed of light? Of course, that’s a trick question. The speed of light may be constant, but just as sound travels at different speeds in different media, electronic signals move through transmission lines at a reduced speed. When you have a known cable, you can look up the velocity factor and use it to approximate the length of cable to have a given effective length. But what if you don’t know what kind of cable you have? [More Than Electronics] used a scope to measure it. You can see what he did in the video below.

For example, RG-8/U has a factor of 0.77. Even air isn’t exactly a factor of 1, although it is close enough that, in practice, we pretend that it is. If you wonder why it matters, consider stubs. Suppose you have a 300 MHz signal (handy because that’s 1 meter in wavelength; well, OK, pick 299.792 MHz if you prefer). If you have a quarter wavelength piece of coax shorted at one end, it will attenuate signals at 300 MHz. To understand why, picture the wave on the stub. If the close end of the stub is at 0 volts, then the other end — because it is a quarter wavelength away — must be at the maximum positive voltage or the minimum negative voltage. If either of the extremes is at the close end, then the far end must be at zero volts. That means the maximum current flows only when the signal is at 300 MHz.

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Crystal Radio Kit From The 1970s

April 19, 2024 by Al Williams 19 Comments

If you read the December 1970 issue of Mechanix Illustrated, you’d be treated to [Len Buckwalter]’s crystal radio build. He called out Modern Radio Labs as the supplier for parts. That company, run by [Elmer Osterhoudt], got so many inquiries that he produced a kit, the #74 crystal set. [Michael Simpson] found an unopened kit on eBay and — after a bidding war, took possession of the kit. The kit looked totally untouched. The crystal detector was still in the box, and there were period-appropriate newspaper wrappings.

The kit itself isn’t that remarkable, but it is a classic. An oatmeal box serves as a coil form. There’s a capacitor, a crystal detector, and headphones. The original cost of the parts was $7, but we imagine the eBay auction exceeded that by a large amount.

If the name [Len Buckwalter] sounds familiar, he was quite prolific in magazines like Electronics Illustrated and also wrote several books about transistors. [Michael] also shows off his innovative coil winder made from plastic cups and a coat hanger.

We’d love to find some old kits like this, although, from one way of thinking, it is almost a shame to build them after all these years. With an added audio amplifier and fiddling with the cat whisker, it sounded just fine.

If you don’t like oatmeal, you could fire up the 3D printer. While the basic circuit is simple, you can make it more complex if you like.

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Hackaday Podcast Episode 267: Metal Casting, Plasma Cutting, And A Spicy 555

April 19, 2024 by Al Williams 3 Comments

What were some of the best posts on Hackaday last week? Elliot Williams and Al Williams decided there were too many to choose from, but they did take a sampling of the ones that caught their attention. This week’s picks were an eclectic mix of everything from metal casting and plasma cutters to radio astronomy and space telescope budgets. In between? Some basic circuit design, 3D printing, games, dogs, and software tools. Sound confusing? It won’t be, after you listen to this week’s podcast.

Check out the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Download an audiophile-quality oxygen-free MP3 file here.

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PC Watercooling Prototype Is Pumpless

April 18, 2024 by Al Williams 23 Comments

Watercooling is usually more efficient than air cooling for the same volume of equipment, and — important for many people — it is generally quieter. However, you still have water pump noises to deal with. [Der8auer] got a Wieland prototype cooler that doesn’t use a pump. Instead, it relies on the thermosiphon effect. In simple terms, the heat moves water — possibly boiling it — upwards to a radiator. Once the water is cool, it falls down back to the heat exchanger again.

It looks like any other AIO, but the block is extremely flat compared to normal coolers, which have the pump on top of the plate. As you might expect, orientation matters, and you can’t have tight bends in the hoses. The system also has to be totally airtight to function properly. The test was meant to be against a commercial AIO unit with the same number of fans. However, there was a problem, and the final test was done with a larger radiator with one of its three fans removed.

The prototype performed fine and was quiet. It didn’t do as well as the commercial cooler, but it wasn’t bad. Of course, this is a prototype. Maybe a final product will do better. Around the ten-minute mark, the IR camera came out, and it didn’t show any major unexpected hot spots.

We’ve seen water-cooled printer hotends, and pumping is a problem there. We wondered if this technology might work there. The whole thing reminded us of heat pipes without the internal wick to move cold working fluid. We’ve even seen a water-cooled calculator.

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Computing Via (Virtual) Dominos

April 18, 2024 by Al Williams 6 Comments

Back in 2012, [Matt Parker] and a team built a computer out of dominos for the Manchester Science Festival. [Andrew Taylor], part of the team that built the original, has built a series of virtual domino puzzles to help explain how the computer worked. He also links to a video from the event, but be warned: the video contains some spoilers for the puzzles. If you are ready for spoilers, you can watch the video below.

The original computer could add two three-bit numbers and provide a four-bit result. We don’t want to give away the answers, but the inverter is quite strange. If you don’t want to puzzle it out, you can press the “reveal answer” to see [Andrew’s] solutions. Press “play” and watch the dominos fall.

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