Colorizer for ZX81 clone

[danjovic] is a vintage computer enthusiast and has several old computers in his collection. Among them are a couple of TK-85 units – a ZX81 clone manufactured by Microdigital Eletronica in Brazil. The TK-85 outputs a monochrome video output. And when [danjovic] acquired a SyncMaster 510 computer monitor, he went about building a circuit to “colorise” the output from the ZX81 clone (Portuguese translation).

The SyncMaster 510 supports 15kHz RGB video refresh rate, so he thought it ought to be easy to hook it up to the TK-85, which internally has the video and composite sync signals available. So, if he could lower the amplitude of the video signal to 0.7Vpp, using resistors, and connect this signal to one of the primary colors on the monitor, for example green, then the screen should have black characters with a green background.

DSCN5584-thumbBefore he could do any of this, he first had to debug and fix the TK-85 which seemed to be having several age related issues. After swapping out several deteriorating IC sockets, he was able to get it running. He soldered wires directly to one of the logic chips that had the video and sync signals present on them, along with the +5V and GND connections and hooked them up to a breadboard. He then tested his circuit consisting of the TTL multiplexer, DIP switches and resistors. This worked, but not as expected, and after some digging around, he deduced that it was due to the lack of the back porch in the video signal. From Wikipedia, “The back porch is the portion of each scan line between the end (rising edge) of the horizontal sync pulse and the start of active video. It is used to restore the black level (300 mV.) reference in analog video. In signal processing terms, it compensates for the fall time and settling time following the sync pulse.”

To implement the back porch, he referred to an older hack he had come across that involved solving a similar problem in the ZX81. Eventually, it was easily implemented by an RC filter and a diode. With this done, he was now able to select any RGB value for foreground and background colors. Finally, he built a little PCB to house the multiplexer, DIP switches and level shifting resistors. For those interested, he’s also documented his restoration of the TK-85 over a four-part blog post.

Interview with the Creators of CHIP, a $9 Single-Board Computer

Single-board computing is hot on the DIY scene right now and riding that knife edge is C.H.I.P., a project currently in crowd-funding which prices the base unit at just $9. I was happy to run into the crew from Next/Thing Company who developed C.H.I.P. They were happy because, well, the project’s reception has been like a supernova. Right now they’re at about $1.5M of their original $50k goal. We spoke about running Linux on the board, what connectors and pinout headers are available, as well as the various peripheral hardware they have ready for the board.

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Relays Calculate Square Roots

After seeing an exhibit of an old relay-based computer as a kid, [Simon] was inspired to build a simple two-relay latching circuit. Since then, he’s been fascinated by how relays can function to do computation. He’s come quite a long way from that first latching circuit, however, and recently finished a huge five-year project which uses electromechanical relays to calculate square roots.

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The frame of the square root calculator can hold up to 30 identical relay modules, each of which hold 16 relays on PCBs, for a total of 480 relays. The module-based setup makes repair and maintenance a breeze. Numbers are entered into the computer by a rotary dial from an old phone and stored in the calculator’s relay memory. A nixie tube display completes the bygone era-theme of the device and shows either the current number that’s being entered, or the square root of that number as it’s being calculated.

The real magic of this project is that each relay has an LED which illuminates whenever the relay is energized, which shows the user exactly where all of the bits of the machine are going. [Simon] worked on this project from 2009 and recently completed it in 2014, and it has been featured at the San Mateo Maker Faire and at Microsoft Research in Redmond, WA. We’ve seen smaller versions of this before, but never on this scale and never for one specific operation like square roots.

Video below. Thanks to [Bonsaichop] for the tip!

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Excruciating Quest Turns Chromebook Pixel IPS Into Exquisite Extra Monitor

[Shen] wanted an extra monitor at his desk, but not just any monitor. He wanted something particularly special and unquestionably refined. Like any super-power-possessing engineer he set out to scratch his hacking itch and was sucked into a multi-year extravaganza. For the love of everything hardware we’re glad this one came in on the weekend. If we had spent all that time drooling during a weekday we’d be so far behind.

The final product is a desktop monitor on an articulated arm. It features a Chromebook Pixel’s IPS display in a custom-crafted case everything. The journey started out with two different LCD units, the first from a Dell L502x replacement display using a generic LVDS board. The results were meh; washed out colors and obvious pixellation, with display adjustments that left [Shen] with a grimace on his mug. Installment two was an iPad Retina display. This iteration required spinning his own boards (resulting in [Shen’s] discovery of OSH Park). Alas, 9.7″ was too small coupled with short-cable-requirements making this version a no-go.

chromebook-pixel-ips-driver-boardAnd so we arrive at the meat and potatoes of this one. [Shen] identified the IPS LCD display on Google’s first Chromebook Pixel laptop as the object of his desire. The hack takes him through sourcing custom display cables, spinning rev after rev of his own board, and following Alice down the rabbit hole of mechanical design. Nothing marginal is good enough for [Shen], we discovered this with his project to get real audio out of a computer. He grinds away at the driver board, the case design, the control presentation, and everything else in the project until perfection was reached. This work of art will stand the test of time as a life fixture and not just an unappreciated workhorse.

This one is not to me missed. Head over to [Shen’s] project entry on Hackaday.io (don’t forget to give him a skull for this) and his blog linked at the top. We need to celebrate not only the people who can pull off such amazing work. But also the ones who do such a great job of sharing the story both for our enjoyment, and to inspire us.

Moore’s Law of Raspberry Pi Clusters

[James J. Guthrie] just published a rather formal announcement that his 4-node Raspberry Pi cluster greatly outperforms a 64-node version. Of course the differentiating factor is the version of the hardware. [James] is using the Raspberry Pi 2 while the larger version used the Model B.

We covered that original build almost three years ago. It’s a cluster called the Iridris Pi supercomputer. The difference is a 700 MHz single core versus the 900 Mhz quad-core with double-the ram. This let [James] benchmark his four-node-wonder at 3.048 gigaflops. You’re a bit fuzzy about what a gigaflops is exactly? So were we… it’s a billion floating point operations per second… which doesn’t matter to your human brain. It’s a ruler with which you can take one type of measurement. This is triple the performance at 1/16th the number of nodes. The cost difference is staggering with the Iridris ringing in at around £2500 and the light-weight 4-node built at just £120. That’s more than an order of magnitude.

Look, there’s nothing fancy to see in [James’] project announcement. Yet. But it seems somewhat monumental to stand back and think that a $35 computer aimed at education is being used to build clusters for crunching Ph.D. level research projects.

What Is This? A Computer for Ants!?

How can we be expected to teach children use a computer if they can’t even see it? I don’t wanna hear your excuses! The computer has to be at least… three times bigger than this!

Developed by the University of Michigan, the Michigan Micro Mote (M3) is quite possibly the world’s tiniest computer. It’s about the size of a grain of rice.

The multi-layered PCB (shown after the break) features 7 layers of components, surrounded in epoxy for protection. Drawing only 2 nano Amps during standby, the computer can be powered by a 1 millimeter squared solar cell. It’s designed to be glued to a window for use. It’s capable of input data via sensors, the ability to process and store the data, and then output the data wirelessly. Its range is only 2 meters at the moment, but they hope to extend it to about 20 meters.

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The RUM 80 – a home brew Z80 computer built from scratch

[M] recently tipped us off about hacker [Lumir Vanek] from the Czech Republic. Between 1985 and 1989, [Lumir] built his own home brew, Z80 based computer. The list of home computers available in the 1980’s is extensive. Those living in western Europe and the Americas could choose offerings from Acorn, Apple, Commodore, Atari, Radio Shack, and Sinclair Research to name just a few. Even the erstwhile Czechoslovakia had home computers available from Didaktik and Tesla.

[Lumir]’s built was based around the Z80 processor and is built using regular, double-sided, prototyping board. It featured the 8-bit Z80 processor CPU, 8kB EPROM with monitor and BASIC, two Z80 CTC timers, an 8255 parallel interface for keyboard and external connector, 64kB DRAM, and Video output in black & white, 40×25 characters, connected to a TV. The enclosure is completely made from copper clad laminate. [Lumir] documented the schematics, but there is no board layout – since the whole thing was discrete wired. He even built the membrane keyboard – describing it as “layers of cuprextit, gum, paper with painted keys and transparent film”. When he ran out of space on the main board, he built an expansion board. This had an 8251 serial interface for cassette deck, one 8-bit D/A converter, and an 8255 parallel port connected to the “one pin” BT100 printer.

On the software side, he wrote his own monitor program, which allowed simple interactions, such as displaying and modifying registers, memory, I/O ports and to run programs. He wrote this from scratch referring to the Z80 instruction set for help. Later he added a CP/M emulator. Since the Z80 had dual registers, one was used for user interaction, while the other was reserved to allow background printing. Eventually, he even managed to port BASIC to his system.

Check out [Martin Malý]’s awesome article Home Computers behind the Iron Curtain and the follow up article on Peripherals behind the  Iron Curtain, where you can read more about the “one pin” BT100 printer.

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