Minivac 601 Replica Gets A Custom Motorized Rotary Switch

July 13, 2019 by Dan Maloney 2 Comments

One of the joys of electronics as a hobby is how easy it is to get parts. Literally millions of parts are available from thousands of suppliers and hundreds of distributors, and everyone competes with each other to make it as easy as possible to put together an order from a BoM. If you need it, somebody probably has it.

But what do you do when you need a part that doesn’t exist anymore, and even when it did was only produced in small numbers? Easy – you create it yourself. That’s just what [Mike Gardi] did with this unique motorized rotary switch he needed to complete his replica of a 1960s computer trainer. We covered his build of the Minivac 601, a trainer from the early computer age that let experimenters learn the ropes of basic digital logic. It used mostly relays, lamps, and switches connected by jumpers, but it had one critical component – a rotary control that was used for input and, with the help of a motor, as an output indicator.

[Mike]’s version of the switch is as faithful to the original as possible, at least in terms of looks. The parts are mostly 3D-printed, with 16 reed switches embedded in the walls and magnets placed in the rotor. The motor to operate the rotor is a simple gear motor mounted to a hinged bracket; when the rotor needs to move, a solenoid pulls the motor’s friction drive wheel up against the rotor.

The unique control slots right into the Minivac replica and really completes the look and feel. Hats off to [Mike] for a delightful replica of a lost bit of computer history and the dedication to see it through to completion.

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Amiga In The MiST Gets Online With An ESP8266

July 3, 2019 by Tom Nardi 9 Comments

While he couldn’t quite come up with the cash to buy one in their hayday, [Bruno Antunes] has always been fascinated with the Amiga. When PCs got fast enough he used emulators like UAE to get a taste of the experience, but it was never quite the same thing. Not until he found the MiST anyway, which uses an FPGA to implement several retro computers such as the Apple II, Atari, and of course his beloved Amiga.

The only downside for [Bruno] was that the MiST has no network interfaces. To get onto the Internet, he had to install an ESP8266 inside the device and spend some quality time tweaking various software settings to get everything talking to each other. The end result is a BBS hosted on an Amiga 1200, that’s running on an FPGA, that’s connected to WiFi via an ESP8266. What a time to be alive.

Adding the ESP8266 to the MiST was actually quite straightforward, as there’s an unpopulated serial port header right on the board. Though [Bruno] cautions this header has been removed as of version 1.4 of the device, so if you’re in the market for an FPGA retro box and might want to get it online at some point, that may be a detail to keep in mind. The ESP is running a firmware which implements Serial Line IP (SLIP); which allows you to use TCP/IP over a serial port, albeit very slowly.

The hardware implant went well enough, but unfortunately [Bruno] found the ESP8266 was unable to communicate through the thick metal case of the MiST. He enlisted his girlfriend to make a new papercraft enclosure for the MiST that the ESP could talk though, and it even has the added benefit of glowing thanks to the internal LEDs. We probably would have just got one of the ESP modules that includes an external antenna, but to each their own.

With the hardware taken care of, the rest of the considerable write-up details how he got the Amiga operating system to talk to the Internet through the SLIP connection. He goes over everything from setting the system time with NTP to getting a Telnet daemon installed. As you might expect, this involves installing a number of additional software packages, but [Bruno] is kind enough to provide links for everything you’ll need.

We’ve seen the ESP8266 used to get other retro computers onto the modern Internet before, but it’s usually through the use of an external device. This internal modification is very clean, and seems like a no-brainer for anyone who owns a MiST and a soldering iron.

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Emulating A 6502 In ROM

July 2, 2019 by Brian Benchoff 25 Comments

The Gigatron TTL microcomputer is an exercise in alternative history. What if, by some bizarre anomaly of invention and technology, the 1970s was not the age of the microprocessor? What if we could have had fast, high density ROM and RAM in the late ’70s, but the ability to put a microprocessor in silicon was beyond our comprehension? Obviously we would figure out a way to compute with this, and the Gigatron is the answer. It’s a computer from that era that’s designed with a CPU that’s entirely made of microcode.

While the Gigatron is a popular product in the world of weird electronics kits, the creator, [Marcel van Kervinck], is going beyond what anyone thought possible. Now the Gigatron is emulating a 6502 processor, the same CPU found in the Apple II and almost every other retrocomputer that isn’t running a Z80.

There’s a thread over on the Gigatron forums for this. Although it’s still very early in development, the Gigatron can now run 6502 machine code, and in doing so the Gigatron is now the only dual-core computer without a CPU. All of the addressing modes have been implemented, along with half of the instructions and most of the status flags. All of this interacts with the Gigatron’s existing video subsystem, and all code can switch in between the Gigatron’s virtual CPU and 6502 code with just a few instructions.

This opens the door to a wide variety of software that’s already written. MicroChess is possible, as is MS Basic. This is great; the biggest downside of the Gigatron is that there was no existing code for the machine when it was first designed. That changed when the Gigatron got a C compiler, but now somehow we’ve got a logic chip implementation of a 6502 in far fewer chips than are found in an Apple II. It’s not fast ( about 1/8th the speed of a 1 MHz 6502), but in the video below you can see a munching squares demo.

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Bit Preserve: A Sanctuary For Modern Captures Of Vintage Schematics

June 25, 2019 by Donald Papp 5 Comments

Vintage parts may be documented, but that doesn’t mean they’re particularly useful or accessible. If the phrase “eyestrain from unsearchable, badly-scanned PDF datasheets” makes your lower eyelid twitch in sympathy, read on.

While [Bald Engineer] was researching how he might make a portable Apple II, he was delighted to find that the vintage components he needed to examine were documented. However, he became frustrated with the seemingly endless number of poor quality PDF scans and the inability to search effectively. He decided to re-create the entire Apple IIgs schematic in KiCad, and in the process the Bit Preserve project was born. The goal is to act as a safe haven for modern and editable versions of vintage electronic schematics. The GitHub repository can be found here.

[Bald Engineer] talks a bit about his Apple II project, as well as the ideas behind the Bit Preserve project in his KiCon 2019 talk “Preserving History with KiCad”. KiCon was wild, and we have loads of photos of the projects and details so be sure to check it out.

The Benefits Of Restoring A C64 With A Modern FPGA Board

June 23, 2019 by Zoe Skyforest 7 Comments

The Commodore 64 was the highest selling computer of all time, and will likely forever remain that way due to the fragmentation of models in the market ever since. Due to this, it’s hardly surprising that it still has a strong following many years after its heyday. This means that the avid restorer has a wide range of parts and support available at the click of a button. [DusteD] is just one such person who had a busted-up C64 laying around, and decided to make it a project.

[DusteD] wanted to reuse the original case, and decided it should remain a Commodore 64 after an initial attempt at a mini-ITX swap went awry. Desiring a reliable machine, an Ultimate64 FPGA board was selected to replace the original faulty motherboard. This has the benefit of being hardware compatible with the classic C64, while allowing [DusteD] to tinker and program to his heart’s content, without having to worry about blowing up valuable original parts. It also provides several interesting modern features, like HDMI output, USB, and even Ethernet connectivity. This allows one to experiment with the platform without the hassles of all the inherent limitations of 1980s technology.

As a fan of the classic SID sound chip, [DusteD] was also highly interested in the audio output of the Ultimate64. Recordings were made of the emulated output from the FPGA, as well as the sound output from a real SID installed in the board, both through the mixed output and directly from the chip via a SIDTAP. Those interested can download the 800MB of recordings and compare the output; there’s a summary of the differences noted listed on the site as well.

[DusteD] makes a great argument for the benefits of building up a C64 rig in this way. It’s a great way to get started for those eager to explore the world of Commodore’s 8-bit hardware without the hassles and expenses of buying all the real gear. As it stands, the C64 aftermarket is so advanced now, that you can build an entirely new machine from scratch if you so desire. Go forth and enjoy!

VR On The 6502

June 23, 2019 by Zoe Skyforest 6 Comments

The MOS Technology 6502 was one of the more popular processors of the 1980s. It ran the Commodore 64, the NES in a modified form, and a whole bunch of other hardware, too. By modern standards, it’s barely fit to run a calculator, but no matter – [Nick Bild] built a VR game that runs on the retro CPU anyway!

[Nick]’s project is built on his 6502 computer, the Vectron 64. Being a breadboard build, it’s easy to modify things and add additional hardware, and that’s precisely what he did. The VR system uses two 320 x 240 LCD screens, one for each eye. These are controlled over SPI, but the humble 6502 simply doesn’t have the speed to clock out enough bits fast enough for a video game. Instead, additional hardware is added to generate pulses to run the screens. There’s a bunch of other neat hacks as well that help make the game playable, like overclocking the CPU to 1.75 MHz and drawing common elements to both screens at the same time.

To test out the VR system, [Nick] coded a basic Asteroids VR game. It’s not really practical to demonstrate the game without the hardware, but we’d love to try it out. There’s something compelling about a low-resolution VR game with 8-bit graphics, and we hope to see the concept further developed in future.

More grunt would make this project even more capable, and for that, a 6502 running at 20MHz could come in handy. Video after the break.

[Thanks to Fred Gimble for the tip!]

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A TTL CPU, Minimising Its Chip Count

June 23, 2019 by Jenny List 19 Comments

By now we should all be used to the astonishing variety of CPUs that have come our way created from discrete logic chips. We’ve seen everything from the familiar Von Neumann architectures to RISC and ever transport-triggered architecture done in 74 TTL derivatives, and fresh designs remain a popular project for many people with an interest in the inner workings of a computer.

[Warren Toomey]’s CSCvon8 is an interesting machine that implements an 8-bit computer with a 64-bit address space using only 17 chips, and without resorting to any tricks involving microcontrollers. It implements a fairly conventional Von Neumann architecture using TTL with a couple of tricks that use modern chips but could have been done in the same way in decades past. Instruction microcode is stored in an EEPROM, and the ALU is implemented in a very large EPROM that would probably once have been eye-wateringly expensive. This in particular removes many discrete TTL chips from the total count, in the absence of the classic 74181 single-chip part. To make it useful there is 32k each of RAM and EEPROM, and also a UART for serial access. The whole is brought together on a neat PCB, and there is a pile of demo code to get started with. Everything can be found in the project’s GitHub repository.

At the start of this article we mentioned a couple of unconventional TTL CPUs. The transport triggered one we featured in 2017, and the RISC one is the Gigatron which has appeared here more than once.