An Amiga 500 For The 21st Century

There was a period in the late 1980s when the home computer to own did not come with an Apple logo and was not an IBM, Compaq, or any of the other clones, but instead sported a Commodore logo. The Amiga 500 was an all-in-one console-style cased machine that maybe wasn’t quite the computing powerhouse you might have wished it to be, but gave you enough of the capabilities of the more accomplished 16-bit machines of the day to be an object of desire while also having a games catalogue second to none.

A500s have survived in reasonable numbers, but inevitably working A500s haven’t. Fortunately there are decent emulators, and it was for one of these that [intric8] has produced an extremely well-done installation of a Raspberry Pi 3 in an Amiga case. The intention has been throughout to avoid modification or damage to the Amiga case, and eventually to have all Amiga internal peripherals including the floppy drive in a fully working condition.

The result has a Tynemouth Software USB adaptor for the Amiga keyboard, and a set of nicely designed 3D printed backplates to bring the extended Raspberry Pi ports to the back of the case. The floppy isn’t yet interfaced and there isn’t a socket for the quadrature mouse, but otherwise it’s a very tidy build. He might be interested in one of the several USB to quadrature interfaces we’ve featured over the years.

You might ask why so much effort should be put in for an emulation of an A500, and in a sense you’d be right to do so. The Pi will run the emulator from any case or none. But if you happen to have a spare A500 case, why not give this one a go!

Converting Power Supplies for Antique Computers

Just because something is “never used” doesn’t mean it’s good. [Inkoo Vintage Computing] learned that lesson while trying to repair an Amiga 500 and finding parts online that were claimed to be “new” in that they were old stock that had never been used. The problem was that in the last 30 years the capacitors had dried out, rendering these parts essentially worthless. The solution, though, was to adapt a modern PSU for use on the old equipment.

The first hurdle to getting this machine running again was finding the connector for the power supply. The parts seemed to have vanished, with some people making their own from scratch. But after considering the problem for a minute longer they realized that another Commodore machine used the same parts, and were able to source a proper cable.

Many more parts had to be sourced to get the power supply operational, but these were not as hard to come across. After some dedicated work with the soldering iron, the power supply was put to use running the old Amiga. Asture readers will know that [Inkoo Vintage Computing] aren’t strangers to the Amiga. They recently were featured with a nondestructive memory module hack that suffered from the same parts sourcing issues that this modification had, but also came out wonderfully in the end.

Respectfully Modifying the Amiga 500

Modifying the Amiga 500 to speed up access to RAM in a memory expansion pack is a well documented procedure, with guides on the process written in the early 1990’s when the hardware was only a few years old. But as they were written for contemporary hardware, they make no concessions for how one should be treating a vintage computer that’s now over 30 years old. In 1993, cutting traces on the Amiga 500 motherboard was just a last ditch effort to eek a few more months of service life out of an outdated desktop computer. But in 2018, it’s kind of like when that old lady tried to “restore” a fresco of Jesus in Spain; it might be done with the best of intentions, but you still screwed the thing up good and proper.

Such things don’t fly over at [Inkoo Vintage Computing]. There you can find a guide that details the impressive lengths one can go to if they want to perform the classic modification without any irreversible changes to the motherboard. To avoid the cut traces and soldered bodge wires, this version of the modification makes use of a novel adapter that breaks out the necessary connections on the 8372A chip.

The adapter is simply a homemade PCB with both male and female plastic leaded chip carrier (PLCC) connectors. The few pins on the chip that needed rerouting are exposed as solder pads on the adapter for easy wiring. There are even a couple jumpers on the adapter to turn the modifications on and off.

Not surprisingly, the trickiest part of building this adapter was sourcing the antiquated PLCC connectors. Assuming you can even find them, you are then left with the challenging task of soldering them together. Judging by the pictures on the [Inkoo Vintage Computing] page, it’s no walk in the park.

Another similar arrangement is used in the expansion bay of the Amiga, where a pin is virtually “cut” in the connector. A tiny PCB is soldered to a 3×2 header to reroute the signals, and another jumper is used to enable and disable the pin. Luckily, the long pins on the Amiga memory expansion are forgiving enough that the little board can fit in between them without breaking electrical contact.

We’re no stranger to the Amiga 500 around these parts. We’ve covered how to get the 1987-vintage machine online in the 21st century, as well as employing a Raspberry Pi to emulate the original floppy drive. You can even make your own faux-Amiga with a 3D printed case, if you suffer from a sort of existential dread when working on a computer that’s older than you are.

Getting The Amiga 500 Online

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.

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Raspberry Pi Emulates an Amiga 500 Floppy Drive

[Maurizio] loves using his Amiga 500. His classic piece of hardware has been serving him well for years, except for the floppy drive, which recently gave out on him. No problem for [Maurizio], he just cracked his case open and added a Raspberry Pi as a real-time floppy emulator. [Maurizio] didn’t want to make any permanent changes to his A500 case, and more importantly he wanted to use the Amiga’s original floppy drive interface. The latter placed some rather stringent timing requirements on his design.

The interface hardware is relatively simple. Most of the circuit is dedicated to level shifting from the 5v Amiga 500 to the 3.3V Raspberry Pi. A 74LS06 Hex inverter converts the signals to the open collector outputs the A500 requires. [Maurizio] powered his Raspberry Pi from the floppy power connector of the Amiga. His model A Raspberry Pi works fine, but a model B would pull a bit more power (700ma) than the Amiga floppy power supply is capable of providing (550ma). The user interface side of the equation is simple: Two buttons, one used to switch disks, and one to “Write to SD”. Live disk images are stored in the Raspberry Pi’s ram, so the user needs to hit the “Write to SD” button to store any changes to disk before swapping floppies.

The software is perhaps the most interesting portion of this build. [Maurizio] is emulating a floppy drive in real-time – this means emulating MFM encoding in real time. Calls have to be made with a timing accuracy of 2 microseconds. The Pi’s stock Linux Operating system was just not going to cut it. [Maurizio] coded his drive emulator “bare metal”, directly accessing the Arm Processor on the Raspberry Pi. This gave him access to the entire processor, and allowed him to meet the hard timing requirements of the floppy interface.

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