SCSI Emulation Of A Rare Peripheral For The Acorn BBC Micro

January 11, 2017 by Jenny List 24 Comments

Mass storage presents a problem for those involved in the preservation of older computer hardware. While today’s storage devices are cheap and huge by the standards of decades ago their modern interfaces are beyond the ability of most older computers. And what period mass storage hardware remains is likely to be both unreliable after several decades of neglect, and rather expensive if it works due to its rarity.

The Domesday Project 86 team face this particular problem to a greater extent than almost any others in the field, because their storage device is a particularly rare Philips Laser Disc drive. Their solution is the BeebSCSI, a small board with a CPLD and an AVR microcontroller providing host adaptor and SCSI-1 emulation respectively for a modern micro-SD card.

An original BBC Domesday set-up. Regregex [CC BY 3.0], via Wikimedia Commons.

1986 saw the 900th anniversary of the Domesday Book, a survey and inventory of his new kingdom commissioned in 1086 by the Norman king of England, William the Conqueror. One of the ways the event was marked in 1986 was the BBC Domesday Project, a collaboration between the BBC, several technology companies including Acorn and Philips, and a huge number of volunteers from the general public and the British school system. Pictures, video, and text were gathered relating to locations all over the country, and the whole was compiled with a not-quite-hypertext interface onto a set of Laser Disc ROMs. The system required the upgraded Master version of the 6502-based BBC Micro, a SCSI interface, and a special Laser Disc player model manufactured by Philips for this project alone. The hardware was expensive, rare, and unreliable, so few of its contributors would have seen it in action and it faded from view to become a cause celebre among digital archivists.

There have been several resurrections of the project over the years, including one from the BBC themselves which you can browse online. What makes this project different from the others is that it strives to present the Domesday experience as it was originally intended to be viewed, on as far as possible the original hardware and with the original BBC Micro interface. Many original parts such as BBC Master systems are relatively easy to source in 2016, but the special Laser Disc player is definitely not. This board replaces that impossible link in the chain, and should allow them to present a glimpse of 1986 in more than just the on-screen information.

If you would like to see an original BBC Domesday Project system, you can find one in action at the National Museum of Computing, at Bletchley Park. Meanwhile we’ve already featured another peripheral from the same stable as this one, the SmallyMouse USB-to-quadrature mouse emulator.

A Portable Jacob´s Ladder

January 8, 2017 by Manuel Rodriguez-Achach 16 Comments

A Jacob´s ladder is a favorite project of high voltage enthusiasts. It makes a visually attractive and fun display of a high voltage electrical arc climbing a pair of electrodes. [Keystone Science] shows us how to make a Jacob´s ladder that runs on 9 V batteries.

The ladder itself is pretty easy to make. It is nothing more than a pair of stiff wires in a V shape, connected to a high voltage power supply. The more difficult part is the HV power supply. [Keystone Science] explains how to build one using a flyback transformer from an old CRT tv and a few other components. It is a pretty simple circuit and can be powered by a 9 V battery. The ladder works because, when HV is applied to the electrodes, an arc is established at the bottom, where they are nearest each other. The arc is at high temperature so the air rises, and the arc starts to climb the ladder. Since the electrodes are further away from each other as the arc rises, at a certain point the distance is too large to sustain the arc and the process repeats.

This is a nice weekend project if you want to try it. In case you don´t want to make your own HV power supply, you can try another ladder project that uses a commercial one.

Yes, You Can Reverse Engineer This 74181

January 7, 2017 by Mike Szczys 21 Comments

[Ken Shirriff] is the gift that keeps on giving this new year. His latest is a reverse engineering of the 74181 Arithmetic Logic Unit (ALU). The great news is that the die image and complexity are both optimized for you to succeed at doing your own reverse engineering.

We have most recently seen [Ken] at work explaining his decapping and reverse engineering process at the Hackaday SuperCon followed soon after by his work on the 8008. That chip is crazy with complexity and a die-ogling noob (like several of us on the Hackaday crew) stands no chance of doing more than simply following along with what he explains. This time around, the 74181 is just right for the curious but not obsessed. Don’t believe me? The 8008 had around 3,500 transistors while the friendly 74181 hosts just 170. We like those odds!

A quick crash course in visually recognizing transistors will have you off to the races. [Ken] also provides reference for more complex devices. But where he really saves the day is in his schematic analysis. See, the traditional ‘textbook’ logic designs have been made faster in this chip and going through his explanation will get you back on track to follow the method behind the die’s madness.

[Ken] took his own photograph of the die. You can see the donor chip above which had its ceramic enclosure shattered with a brisk tap from a sharp chisel.

Amstrad On An FPGA

January 6, 2017 by Al Williams 22 Comments

If you are from the United States and of a certain age, it is very likely you owned some form of Commodore computer. Outside the US, that same demographic was likely to own an Amstrad. The Z80-based computers were well known for game playing. [Freemac] implemented a working Amstrad CPC6128 using a Xilinx FPGA on a NEXYS2 demo board.

The wiki posting is a bit long, but it covers how to duplicate the feat, and also gives technical details about the design. It also outlines the development process used ranging from starting with a simple Z80 emulation and moving on to more sophisticated attempts. You can see a video of the device below.

Continue reading “Amstrad On An FPGA” →

Keep An Old Real Time Clock Module Ticking

January 6, 2017 by Adam Fabio 30 Comments

Sometimes we run into real problems restoring old machines. [RedruM69] recently ran into a system with a dead Real Time Clock (RTC) module. These modules were used on computers and all sorts of other equipment, storing time, date, and 100 or so bytes of battery backed SRAM (before the days of cheap, plentiful flash memory). Often an external coin cell would supply power to the module. In some cases though, cost savings would take over, and the battery would be incorporated into the module. Such is the case with many Dallas Semiconductor models, and the benchmarq bq3287 module [RedruM69] was working with. If we’re reading the date code right, the module was produced in mid 1995 so we’re well past the advertised 10 year battery life.

Apparently Texas Instruments is the current owner of this design, and they even have a datasheet online. (PDF link). It turns out that the bq3287 is a descendant of the bq3285, except that the battery pin is internally disconnected. For most people this would mean a search for a compatible replacement. An industrious hacker might even whip up something compatible from modern components. Not [RedruM69] though. He broke out his Dremel tool and cut into the potted case. Exposing the internal connections above pins 16 and 20 allowed him to solder two wires on. Connecting these wires to an external coin cell brought the module back to life.

[RedruM69] isn’t the first one to perform this hack. Sun computers kept their MAC address in chips like this. When the battery went dead, the computer was off the network. Hackers have been cutting the modules open and adding batteries for years. You could always forgo RTC modules completely and use the power grid as your timebase.

A Thoroughly Modern Sinclair ZX80

January 5, 2017 by Jenny List 60 Comments

At the end of the 1970s, the 8-bit home computer market had been under way for several years. Companies like Apple and Commodore had produced machines that retain a cult following to this day, and there was plenty for the computer enthusiast to get to grips with. As always though with a new technology, the trouble was that an Apple II or a Commodore Pet wasn’t cheap. If you didn’t have much cash, or you were a young person with uncomprehending or impoverished parents, they were out of reach. You could build a computer from a kit if you were brave or technically competent enough, but otherwise you were out of luck.

As you might imagine, the manufacturers understood that there was an untapped market for cheaper hardware, so as we entered the new decade a range of budget machines that appeared to satisfy that demand. Gone were internal expansion slots, dedicated monitors and mass storage, for cheap keyboards, domestic TV monitors, and home cassette recorders. 1980s teenagers would have computers of their own, their parents safe in the knowledge they were educational while the kids themselves were more interested in the games. Continue reading “A Thoroughly Modern Sinclair ZX80” →

Getting The Amiga 500 Online

January 3, 2017 by Jenny List 43 Comments

If you were lucky enough to have a Commodore Amiga or one of its competitor 16-bit home computers around the end of the 1980s, it’s probable that you were doing all the computing tasks that most other people discovered a few years later when they bought their first 486 or Pentium. So in the mid 1990s when all your friends were exclaiming at Paint Shop Pro or their Soundblaster cards you’d have had an air of smugness. Multitasking? Old hat! Digital audio? Been there! Graphics manipulation? Done that!

There was one task from that era you almost certainly wouldn’t have done on your Amiga though, and that was connect it to the Internet. The Internet was certainly a thing back in the late 1980s, but for mere mortals it was one of those unattainable marvels, like a supercomputer with a padded seat round it, or a Jaguar XJ220 supercar.

Later Amigas received Internet abilities, and Amiga enthusiasts will no doubt be on hand to extol their virtues. But the machine most people will think of as the archetype, the Amiga 500, lacks the power to run most of the software required to do it. If your 500 with its tasteful blue and orange desktop colour scheme is languishing though, never fear. [Shot97] has produced a guide to getting it online.

It’s important to understand that an Amiga 500 is never going to run a copy of Chrome or play a YouTube video. And he makes the point that any web browsers that might have surfaced for hardware of this class delivered a painful browsing experience. So instead he concentrates on getting the 500 online for something closer to the online scene of the day, connecting to BBSs. To that end he takes us through setting up a PC with Hayes modem emulator, and connecting it to the Amiga via a null modem cable. On the Amiga is a copy of the A-Talk terminal emulator, and as far as the Amiga is concerned it is on a dial-up Internet connection.

The PC in this case looks pretty ancient, and we can’t help wondering whether a Raspberry Pi or even an ESP8266 module could be put in its place given the appropriate software. But he has undeniably got his A500 online, and shown a way that you can too if you still have one lurking in the cupboard. He has also produced a video which we’ve put below the break, but be warned, as it’s nearly an hour long.

Continue reading “Getting The Amiga 500 Online” →