Old Casio Calculator Learns New Tricks

April 6, 2022 by Chris Wilkinson 12 Comments

[George Stagg] recently found himself stung by the burden of free time while in lockdown. Needing a project to keep him occupied, he decided to upgrade his 90s Casio CFX-9850G calculator to run custom machine code.

All [George] really wanted was for his vintage calculator to understand Reverse Polish Notation (RPN). The calculator in question can already run its own version of BASIC, however the bespoke Hitachi CPU struggles performance-wise with complex programs, and wouldn’t be a realistic way of using RPN on the calculator. An RPN interpreter written in assembly language would be much faster.

The first step in cracking this calculator wide open was a ROM dump, followed by writing a disassembler. Incredibly, the MAME framework already featured a ‘partial implementation’ of the calculator’s CPU, which was a much needed shot in the arm when it came time to write a full-featured emulator.

With the entire calculator emulated in software, the plan from here involved replacing one of the BASIC commands in ROM with new code that would jump to an address in RAM. With 32KB of RAM there ended up being plenty of room for experimentation, and uploading a program into RAM was simplified by using Casio’s original backup software to dump the RAM onto a PC. Here, the contents of RAM could be easily modified with custom code, then uploaded back into the calculator.

With RAM to burn, new routines were created to write custom characters to the screen, and a new font was created to squeeze more characters onto the display than normal. [George] ended up porting a Forth interpreter, which defaults to RPN style, to finally achieve his humble objective. He also managed to get a version of Conway’s Game Of Life running, check out the video after the break.

We can’t get enough of our calculator hacks here, so make sure to check out the CPU transplant on this vintage Soviet calculator.

Continue reading “Old Casio Calculator Learns New Tricks” →

Pong In Hardware… Virtually

April 6, 2022 by Al Williams 5 Comments

We are big fans of the Falstad circuit simulator. Sure, it isn’t perfect, but there’s nothing else like it when you want to whip up a simple circuit. But we were blown away when we saw a more or less complete hardware implementation of Pong in Falstad. No kidding. Starting with the original schematics, there are multiple pages that show each sub-circuit and even a playable subset that you can play the game in your browser.

But wait… you probably noticed there’s no CRT display in the simulator’s component menu. That’s true, there isn’t. However, you can write JavaScript to interact with a running simulation, so the display is a simple bit of JavaScript that samples signals at predetermined points and does the appropriate drawings. There’s even audio output for the sound effects, although that is built into the simulator.

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A Simple Linear Power Supply, Done Well

April 5, 2022 by Jenny List 45 Comments

When reaching for a power supply design it’s normal here in 2022 to reach for a switching design. They’re lightweight, very efficient, and often available off-the-shelf at reasonable prices. Their benefits are such that it’s become surprisingly rare to see a traditional linear power supply with a mains-frequency transformer and rectifier circuit, so [ElectroBoy]’s dual voltage PSU board for audio amplifiers is worth a second look.

This type of linear power supply has an extremely simple circuit consisting of a transformer, bridge rectifier, and capacitors. The transformer isolates and steps down the AC voltage, the rectifier turns it into a rough DC, and the capacitors filter the DC to remove as much AC ripple as possible. In an audio power supply the capacitors have the dual role of filtering and providing an impulse reservoir for the supply in the event of a peak in demand imposed by the music being played. Careful selection is vital, with in this case a toroidal mains transformer and good quality capacitors being chosen.

The choice between a linear power supply such as this one and a switching design for high quality audio is by no means clear-cut, and may be something we’ll consider in our Know Audio series. The desirable properties are low noise and that impulse reservoir we mentioned, and it’s probably fair to say that while both types of power supply can satisfy them. With the extra expense of a toroidal transformer a linear supply is unlikely to be the cheaper of the two, but we suspect the balance tips in its favour due to a good linear supply being the easier to design.

Levitate The NE555 Way

April 4, 2022 by Jenny List 16 Comments

Ultrasonic levitation — the practice of creating a standing wave between two ultrasonic sources and positioning lightweight objects such that they can float in the pressure minimums between them — has been a source of fascination to more than one experimenter. [Peter Lin] demonstrated this in the video below the break, by creating an ultrasonic levitation system using only the trusted chip of all true experimenters, the NE555. (Video, embedded below.)

The circuit is simplicity itself, just an astable of the type that has made a billion beepers and flashing LEDs. It drives two ultrasonic transducers in parallel, and with them pointing towards each other and a bit of gap adjustment work it can successfully levitate pieces of polystyrene. There was some work in adjusting the frequency to the transducer resonance, but that’s not a huge challenge given the right instrumentation. We can see that it would make a great demonstration of standing waves, and also a fantastic desk toy for not a lot.

We celebrate everyone’s favourite timer chip here at Hackaday, so much so that we recently ran a contest to find the best creations using it.

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Version 1.8 of the 80386 ISA SBC in its assembled glory. (Credit: Alexandru Groza)

Building Your Own 80386DX ISA Single Board Microcomputer

March 30, 2022 by Maya Posch 36 Comments

Having grown up with 386-level systems during the early 90s like so many of us, [Alexandru Groza] experienced an intense longing to experience the nostalgia of these computer systems from an interesting angle: by building his own 80386DX-based single board computer. Courtesy of the 16-bit ISA form factor, the entire system fits into a 16-bit ISA backplane which then provides power and expansion slots for further functionality beyond what is integrated on the SBMC card.

Having started the project in 2019, it is now in the home stretch towards completion. Featuring an 80386DX and 80387DX FPU alongside 128 kB of cache and a grand total of 32 MB of RAM, an OPTi chipset was used to connect with the rest of the system alongside the standard 8042-class PS/2 keyboard and mouse controller. A large part of the fun of assembling such a system is that while the parts themselves are easy enough to obtain, finding datasheets is hard to impossible for some components.

Undeterred, some reverse-engineering of signaling on functional mainboards was sufficient to fill in the missing details. Helpfully, [Alexandru] provides the full schematics and BOM of the resulting board and takes us along with bootstrapping the system after obtaining the PCBs and components. After an initial facepalm moment due to an incorrectly inserted (and subsequently very dead) CPU and boot issues, ultimately [Alexandru] gave up on the v1.6 revision of the board

Fortunately the v1.8 revision with a logic analyzer led to a number of discoveries that has led to the system mostly working, minus what appears to be DMA-related issues. Even so, it is a remarkable achievement that demonstrates the complexity of these old systems.

Finally, The Venerable Vectrex Gets A Mini Makeover

March 29, 2022 by Robin Kearey 16 Comments

It appears that every great console is bound to get a miniature remake: we’ve had the PlayStation Classic, the Mini NES and SNES, and even a miniature Sega Genesis/Mega Drive. But one great console that was sorely missing from that list, at least according to [Brendan], was the Vectrex. So he went ahead and built a fully-functioning miniature Vectrex Console.

If the name “Vectrex” doesn’t ring a bell in your mind, you’re not alone: a commercial failure, it was quickly forgotten by most following the 1983 video game crash. But it has retained a cult status among enthusiasts due to its unique design featuring a monochrome vector monitor, onto which you can place transparent overlays to obtain a sort-of color display. Its games can now all be emulated using software like RetroPie, which is what [Brendan] chose to run on a Raspberry Pi Model 2 that he had lying around.

As for the display, he settled on a Pi-compatible 3.5″ TFT device. Hooking it up to the Pi was easy enough, but getting the image rendered in its proper portrait orientation was quite a headache, requiring endless fiddling with drivers and configuration files.

Once he got this working, [Brendan] set to work designing a miniature copy of the Vectrex’s original case. It took a few iterations and several 10-hour runs on his 3D printer before he ended up with a sturdy case that securely held the Pi and its display in place. A few more hours of printing later he also had a handheld controller, which he based on an Arduino Pro Mega. The Arduino reads out four regular pushbuttons and a joystick, and communicates with the Pi through a coiled USB cable.

The end result, as you can see in the video embedded below, is the cutest little Vectrex we’ve ever seen. It’s really the opposite of this big-screen Vectrex project. We’ve also seen a Vectrex projector, and even one with a real color monitor hacked in. Continue reading “Finally, The Venerable Vectrex Gets A Mini Makeover” →

A Timex Datalink smartwatch next to an Arduino

Arduino Keeps Your Classic Timex Datalink In Sync

March 26, 2022 by Robin Kearey 18 Comments

The Timex Datalink was arguably the first usable smartwatch, and was worn by NASA astronauts as well as geek icons like Bill Gates. It could store alarms, reminders and phone numbers, and of course tell the time across a few dozen time zones. One of the Datalink’s main innovations was its ability to download information from your PC — either through flashing images on a CRT monitor or through a special adapter plugged into a serial port.

With CRTs thin on the ground and original serial adapters fetching ludicrous prices online, classic Datalink users today may find it hard to keep their watches in sync with their Outlook calendars. Fortunately for them, [famiclone] came up with a solution: a DIY Datalink adapter based on an Arduino. It works the same way as Timex’s serial adapter, in that it receives data through the computer’s serial port and transmits it to the watch by flashing a red LED.

Updating your watch does require the use of the original Datalink PC software, which only runs on classic operating systems like Windows 95 or 98, so you’ll need to keep a copy of such an OS running. Luckily, it has no problem with virtual machines or USB COM ports, so at least you don’t need to keep vintage PC hardware around. Then again, whipping out a 1995 Pentium laptop to update your Timex watch would make for the ultimate geek party piece.

Love classic geeky watches? Check out this featured article we did on them a few years ago. If you’re interested in using computer monitors to transmit data optically, we’ve covered a few projects that do just that.