Sinclair I/O Board Completed Over 30 Years Later

November 21, 2016 by Jenny List 15 Comments

In the early 1980s when the 8-bit microcomputer boom was well under way, [Alan Faulds] was a student, and an owner of a Sinclair ZX81. He had ambitions to use it, in his words, “to control the world“, but since the Sinclair lacked an I/O port he was thwarted. He bought an expander board and a couple of I/O card PCBs from the British electronic supplier Maplin in the days when they were a mail order parts stockist rather than a chain of stores chasing Radio Shack’s vacated retail position.

Sadly for [Alan], he didn’t have the cash to buy all the parts to populate the boards, then the pressures of a final year at university intervened, and he never built those Maplin kits. They sat forgotten in their padded envelope for over three decades until a chance conversation with a friend reminded him of his unfinished student project. He sought it out, and set about recreating the board.

The ZX81 had a single port: a PCB edge connector at its rear that exposed all the Z80 processor’s lines. It was notorious for unreliability, as the tiniest vibration when a peripheral was connected would crash the machine. Maplin’s expansion system featured a backplane with a series of edge connector sockets, and cards with bare PCB edge connectors. Back in the 1980s it was easy to find edge connectors of the right size with the appropriate key installed, but not these days. [Alan] had to make one himself for his build.

The I/O card with its 8255 and brace of 74 series chips was a double-sided affair with vias made through the use of little snap-off hand-soldered pins. [Alan] put his ICs in sockets, a sensible choice given that when he powered it up he found he’d put a couple of the 74 chips in the wrong positions. With that error rectified the board worked exactly as it should, giving the little ZX three I/O ports, albeit with one of them a buffered output.

We haven’t featured the little Sinclair micro as often as we should have here at Hackaday, it seems to have been overshadowed by its ZX Spectrum successor. We did show you a VGA ZX81 emulated on an mbed though, and a rather neat color video hack for its Brazilian cousin.

Ruggedizing A Cheap Camera For Spacecraft Testing

November 19, 2016 by Jenny List 13 Comments

Name the countries that house a manned space program. In order of arrival in space, USSR/Russian Federation, United States of America, People’s Republic of China. And maybe one day, Denmark. OK, not the Danish government. But that doesn’t stop the country having a manned space program, in the form of Copenhagen Suborbitals. As the tagline on their website has it: “We’re 50 geeks building and flying our own rockets. One of us will fly into space“. If that doesn’t catch the attention of Hackaday readers, nothing will.

For their rocket testing they need a lot of video feeds, and for that they use cheap Chinese GoPro clones. The problem with these (and we suspect many other cameras) is that when subjected to the temperature and vibration of being strapped to a rocket, they cease to work. And since even nonprofit spaceflight engineers are experts at solving problems, they’ve ruggedized the cameras to protect them from vibration and provide adequate heatsinking.

The heat issue is addressed by removing the camera case and attaching its metal chassis directly to a heatsink that forms the end of an extruded aluminium case. Vibration was causing the camera SD cards to come loose, so these are soldered into their sockets. Power is provided by a pair of 18650 cells with a switching regulator to provide internal power, and another to allow the unit to be charged from a wide range of input voltages. A PCB houses both the regulators and sockets for cable distribution. There is even a socket on top of the case to allow a small monitor to be mounted as a viewfinder. Along the way they’ve created a ruggedized camera that we think could have many applications far beyond rocket testing. Maybe they should sell kits!

We’ve covered Copenhagen Suborbitals before quite a few times, from their earliest news back in 2010, through a look at their liquid-fueled engine, to a recent successful rocket launch. We want to eventually report on this project achieving its aim.

Thanks [Morten] for the tip.

EM Drive Paper Published By Eagleworks Team

November 19, 2016 by Jenny List 131 Comments

There are one or two perennial scientific stories that sound just too good to be true, but if they delivered on their promise would represent a huge breakthrough and instantly obsolete entire fields. One example is so-called “cold fusion”, the idea that nuclear fusion could be sustained with a net energy release at room temperature rather than super-high temperature akin to that of the sun. We all wish it could work, but so far it has obstinately refused. As a TV actor portraying a space engineer of the future once said, one “cannae change the Laws of Physics“.
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Roll Your Own 64GB SD Card From An EMMC Chip

November 18, 2016 by Jenny List 11 Comments

It’s well-known that buying Flash storage devices from cheap online retailers is fraught with danger. Stories abound of multi-gigabyte drives that turn out to be multi-megabyte ones engineered to falsely report their capacity. So when [Jason Gin] found a source of 64GB Toshiba eMMC chips for only $6 per device he bought a few, but was prepared for disappointment.

To test them, he decided to use an SD card interface. There are minor differences between eMMC and SD, but the interfaces are electrically the same and in most cases an SD controller will happily do business with an eMMC. It was not however an easy task to connect the two — these eMMCs were in BGA packages, hardly the easiest ones to work with. He resorted to dead-bug soldering the relevant interface wires to SD lines, and connecting up his computer.

His first attempt was something of a failure, wiring the chip to the PCB of a cheap USB-to-SD adaptor. This did not put him off though, he followed it up by cracking open a very old 2GB SD card that contained a PCB instead of being potted, and soldering his eMMC in place of its Flash and controller. This even fit in the original SD housing, and met with success when plugged into more reliable SD card readers. He was thus able to confirm the capacity of his chips.

His blog post is worth a read for more than just the very fine soldering involved. He takes us through some of the intricacies of SD interfacing, as well as talking at length about the decoupling and termination required to make a reliable connection. We particularly like his use of an area of unconnected BGA balls as prototyping space for decouplers.

If you marvel at the exceptional dexterity required for hand BGA work, we’ve a couple of other treats for you. There is this TI infra-red sensor BGA soldered to a piece of stripboard, and this wafer-level chip package soldered to an SOIC prototyping board.

The BASIC Issue With Retro Computers

November 18, 2016 by Jenny List 91 Comments

If you are interested in how a computer works at the hardware grass-roots level, past all the hardware and software abstractions intended to make them easier to use, you can sometimes find yourself frustrated in your investigations. Desktop and laptop computers are black boxes both physically and figuratively, and microcontrollers have retreated into their packages behind all the built-in peripherals that make them into systems-on-chips.
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Smartphone Bench Instrument Apps: Disappointment Or Delight?

November 17, 2016 by Jenny List 24 Comments

If you are interested in electronics or engineering, you’ll have noticed a host of useful-sounding apps to help you in your design and build work. There are calculators, design aids, and somewhat intriguingly, apps that claim to offer an entire instrument on your phone. A few of them are produced to support external third-party USB instrument peripherals, but most of them claim to offer the functionality using just the hardware within the phone. Why buy an expensive oscilloscope, spectrum analyzer, or signal generator, when you can simply download one for free?

Those who celebrate Christmas somewhere with a British tradition are familiar with Christmas crackers and the oft-disappointing novelties they contain. Non-Brits are no doubt lost at this point… the crackers in question are a cardboard tube wrapped in shiny paper drawn tight over each end of it. The idea is that two people pull on the ends of the paper, and when it comes apart out drops a toy or novelty. It’s something like the prize in a Cracker Jack Box.

Engineering-oriented apps follow this cycle of hope and disappointment. But there are occasional exceptions. Let’s tour some of the good and the bad together, shall we?

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Characterizing A Cheap 500MHz Counter Module

November 16, 2016 by Jenny List 22 Comments

An exciting development over the last few years has been the arrival of extremely cheap instrumentation modules easily bought online and usually shipped from China. Some of them have extremely impressive paper specifications for their price, and it was one of these that caught the eye of [Carol Milazzo, KP4MD]. A frequency counter for under $14 on your favourite online retailer, and with a claimed range of 500 MHz. That could be a useful instrument in its own right, and with a range that significantly exceeds the capabilities of much more expensive bench test equipment from not so long ago.

Just how good is it though, does it live up to the promise? [Carol] presents the measurements she took from the device, so you can see for yourselves. She took look at sensitivity, VSWR, and input impedance over a wide range, after first checking its calibration against a GPS-disciplined standard and making a fine adjustment with its on-board trimmer.

In sensitivity terms it’s a bit deaf, requiring 0.11 Vrms for a lock at 10 MHz. Meanwhile its input impedance decreases from 600 ohms at the bottom of its range to 80 ohms at 200 MHz, with a corresponding shift in VSWR. So it’s never going to match a high-end bench instrument from which you’d expect much more sensitivity and a more stable impedance, but for the price we’re sure that’s something you can all work around. Meanwhile it’s worth noting from the pictures she’s posted that the board has unpopulated space for an SPI interface header, which leaves the potential for it to be used as a logging instrument.

We think it’s worth having as much information as possible about components like this one, both in terms of knowing about new entrants to the market and in knowing their true performance. So if you were curious about those cheap frequency counter modules, now thanks to [Carol] you have some idea of what they can do.

While it’s convenient to buy a counter module like this one, of course there is nothing to stop you building your own. We’ve featured many over the years, this 100MHz one using a 74-series prescaler or this ATtiny offering for example, or how about this very accomplished one with an Android UI?