Behind The Pin: How The Raspberry Pi Gets Its Audio

July 13, 2018 by Jenny List 54 Comments

Single board computers have provided us with a revolution in the way we approach computing as hardware creators. We have grown accustomed to a world in which an entire microcomputer has become a component in its own right rather than a complex system, and we interface to them as amorphous entities through their exposed interfaces. But every pin or socket on a single board computer has something behind it, so following up on a recent news-inspired item in which we took a look at what lies behind the Ethernet jack on a Raspberry Pi, we’d like to continue that theme by looking behind more pins and interfaces. So today we’ll stay with the Raspberry Pi, and start with an easy target by taking a look down its audio jack.

All the main Raspberry Pi board releases since 2012 with the exception of the Pi Zero series, have featured a 3.5mm jack carrying line-level audio. The circuits are readily accessible via the Raspberry Pi website, and are easy enough to understand because of course all the really hard work is done within the silicon of the Broadcom system-on-chip. Looking at the audio circuitry, we’ll start by going back to the original Pi Model B from 2012 (PDF) because though more recent models have seen a few changes, this holds the essence of the circuitry.

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An Amiga 600 With An FPGA Inside

July 10, 2018 by Jenny List 24 Comments

The Amiga is the platform that refuses to die. It must be more than two decades since the debacle surrounding the demise of the original hardware, yet the operating system is still receiving periodic updates, you can still buy Amiga hardware now sporting considerably more powerful silicon than the originals, and its worldwide community is as active as ever.

One of those community projects is the MiSTer FPGA Amiga-on-an-FPGA, and it was this that caught the attention of [Mattsoft]. Impressed with the quality of its recreation of an Amiga, he decided to turn his into a “real” Amiga, so found an Amiga 600 case and keyboard, and set to work. Into the mix went the Terasic DE10-Nano FPGA board, I/O and RAM boards, a Tynemouth Software keyboard interface, a USB hub, and some well-designed 3D-printed parts allow the original Amiga case to be used without modifications.

The Amiga 600 was the base model in the final Amiga range from the early 1990s, and at the time despite its HDD interface and PCMCIA slot it languished in the shadow of its Amiga 1200 sibling. The styling has aged well though, and this upgrade certainly breathes a little life back into the case if not strictly the machine itself. If you want to learn a bit more about MiSTer then a look at the project’s wiki is in order. Perhaps you don’t have an Amiga though and would like to wallow in a bit of nostalgia without splashing out for hardware, in that case, give AROS a look.

Thanks [intric8] for the tip.

Automatic Sunglasses, No Battery!

July 8, 2018 by Jenny List 26 Comments

There are some projects that are so simple they require very little description, and [Bobricius’s] automatic sunglasses definitely fit into that category. Their story starts with the fad for 3D displays a few years ago, a resurfacing of the movie business’s periodic flirtation with the third dimension in the hope of using the gimmick to bring in more moviegoers. There was a time when you could hardly encounter a new TV or graphics card without it coming with a pair of cheap plastic glasses with LCD panels instead of lenses that would alternately shutter the view for each eye to create the 3D illusion.

Of course, once everyone had seen the film with the blue aliens and tried a few other titles on their new toy, they grew tired of headaches, nausea, and half-brightness. The glasses gathered dust, and the fancy 3D telly never ventured beyond two dimensions again. Except for [Bobricius’s] glasses, that is, for he’s levered out the 3D driver electronics and replaced them with a tiny SOIC-8 solar cell. Light hits the cell, the LCD gets a charge and darkens, no light and they remain transparent. Similar to welding goggles — though they usually use a battery. It’s unclear whether they can get a little too dark on a really bright day and whether they are something akin to [Zaphod Beeblebrox]’s peril-sensitive sunglasses, but we really applaud the idea. They are so simple that this Hackaday write-up is probably longer than their write-up, but they remain a neatly executed idea and we like that.

You can, of course, use a battery, or achieve the same effect by more complex means. But if the [Beeblebrox] glasses are closer to your requirements, we’ve got that covered too.

Multi-Board Solder Stencils Explained

July 7, 2018 by Jenny List 13 Comments

There was a time when reflow soldering was an impossibly exotic process at our level, something that only the most superhuman of hackers could even dream of attempting. But a demystification of the process plus the ready availability of affordable PCB and stencil manufacture has rendered into the range of almost all constructors, and it is likely that many of you reading this will have done it yourself.

Screen-printing solder paste onto a single board presents a mild alignment challenge, but how about doing it with many boards at once? [Eric Gunnerson] had this problem with a small-volume board he’s selling, and not being in the happy position of having his PCBs supplied on a panel, had to create his own multi-board alignment jig and stencil. His write-up provides a comprehensive and fascinating introduction to the process whether you are an occasional dabbler or embarking on a production run as he is.

The problem facing any would-be stenciler is that the board has to be held in place reliably in the same alignment as the stencil. With a single board, it’s easy enough to do the usual thing of taping scraps of PCB board to constrain its edges and hold it in place as a rudimentary jig, then lower the stencil onto it. Perhaps you’ve used one of those commercial stencil jigs, in which a set of magnets hold the stencil in place, or maybe you use pins to line everything up.

[Eric] takes us through the process of creating a laser-cut alignment jig for twelve boards, and cutting a matching twelve-board stencil. This includes all the software side using Inkscape, the selection of materials to match PCB thickness, and some of the issues with cutting Mylar sheet for the stencil without shrinkage at the corners. He’s using pins for alignment, and he even finds a handy supply of those in the form of shelf support pins.

We’ve visited the world of reflowing many times before. If you’d like a primer, here’s our Tools of the Trade piece on it, and if you aren’t daunted by larger projects, here’s an account of a prototype run of a significantly complex board.

The PT2399 Delay/Echo Chip Data Sheet You Never Had

July 7, 2018 by Jenny List 13 Comments

If you are fortunate enough to have had the opportunity to play with an analogue-reel-to-reel tape recorder in a well-equipped studio, you probably looped the tape around to create an echo, or a delay in the audio. It was a desirable effect to have, but not a practical one for a guitar pedal or similar portable accessory. Silicon alternatives for creating delays have been in production since the 1960s, first the so-called bucket brigade delay lines that used a switched chain of on-chip capacitors, and more recently all-digital chips that process the delay by storing samples in RAM. One of the more popular of those is the Princeton Technology PT2399, but it comes with something of a snag for the experimenter in the form of a sparse data sheet. Thankfully the folks at [Electrosmash] have come to the rescue on that front with a thorough technical examination of the chip that should fill in any gaps in the official documentation.

After a brief examination of the range of chips of which the 2399 is a part, they dive right into the chip’s internals by rearranging the internal circuit diagram from the data sheet to the point at which it makes more sense. At which point the difference between the chip’s delay and echo functions becomes obvious, through the inclusion of a feedback path.

We then are taken through the pins, examining what lies behind the power supply and analog inputs and outputs. We are somewhere between a data sheet and an app note here, as some of this is information rarely present even in really good data sheets. Finally, we are taken through the chip’s performance, with real-world distortion and noise measurements. Armed with this page, the would-be PT2399 designer really can say they know what they are working with.

Surprisingly few PT2399s have appeared on these pages, however one did pop up in the Synthbike.

An Optical Mouse Sensor For Robotic Vision

July 6, 2018 by Jenny List 22 Comments

Readers with long memories will remember the days when mice and other similar pointing devices relied upon a hard rubber ball in contact with your desk or other surface, that transmitted any motion to a pair of toothed-wheel rotation sensors. Since the later half of the 1990s though, your rodent has been ever significantly more likely to rely upon an optical sensor taking the form of a small CCD camera connected to motion sensing electronics. These cameras are intriguing components with applications outside pointing devices, as is shown by [FoxIS] who has used one for robot vision.

The robot in question is a skid-steer 4-wheeled toy, to which he has added an ADNS3080 mouse sensor fitted with a lens, an H-bridge motor driver board, and a Wemos D1 Mini single board computer. The D1 serves a web page showing both the image from the ADNS3080 and an interface that allows the robot to be directed over a network connection. A pair of LiPo batteries complete the picture, with voltage monitoring via one of the Wemos analogue pins.

The ADNS3080 is an interesting component and we’d love see more of it. This laser distance sensor or perhaps this car movement tracker should give you some more info. We’ve heard rumors of them being useful for drones. Anyone?

Retrotechtacular: Constructing A Car Engine

July 4, 2018 by Jenny List 18 Comments

Oxford is a city world-famous for its university, and is a must-see stop on the itinerary of many a tourist to the United Kingdom. It features mediaeval architecture, unspoilt meadows, two idylic rivers, and a car plant. That’s the part the guide books don’t tell you, if you drive a BMW Mini there is every chance that it was built in a shiny new factory on the outskirts of the historic tourist destination.

A 1930s Morris Ten Series II. Humber79 [CC BY-SA 3.0].

The origins of the Mini factory lie over the road on a site that now houses a science park but was once the location of the Morris Motors plant, at one time Britain’s largest carmaker. In the 1930s they featured in a British Pathé documentary film which we’ve placed below the break, part of a series on industry in which the production of an internal combustion engine was examined in great detail. The music and narration is charmingly of its time, but the film itself is not only a fascinating look inside a factory of over eight decades ago, but also an insight into engine manufacture that remains relevant today even if the engine itself bears little resemblance to the lump in your motor today.

Morris produced a range of run-of-the-mill saloon cars in this period, and their typical power unit was one of the four-cylinder engines from the film. It’s a sidevalve design with a three-bearing crank, and it lacks innovations such as bore liners. The metallurgy and lubrication in these engines was not to the same standard as an engine of today, so a prewar Morris owner would not have expected to see the same longevity you’d expect from your daily.

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