How Did Dolby Digital Sound Work On Film?

April 5, 2022 by Jenny List 26 Comments

When we go to the cinema and see a film in 2022, it’s very unlikely that what we’re seeing will in fact be a film. Instead of large reels of transparent film fed through a projector, we’ll be watching the output of a high-quality digital projector. The advantages for the cinema industry in terms of easier distribution and consistent quality are obvious. There was a period in the 1990s though when theatres still had film projectors, but digital technology was starting to edge in for the sound. [Nava Whiteford] has found some 35mm trailer film from the 1990s, and analysed the Dolby Digital sound information from it.

The film is an interesting exercise in backward compatibility, with every part of it outside the picture used to encode information. There is the analogue sound track and two digital formats, but what we’re interested in are the Dolby Digital packets. These are encoded as patterns superficially similar to a QR code in the space between the sprocket holes.

Looking at the patent he found that they were using Reed-Solomon error correction, making it relatively easy to decode. The patent makes for fascinating reading, as it details how the data was read using early-1990s technology with each line being scanned by a linear CCD, before detailing the signal processing steps followed to retrieve the audio data. If you remember your first experience of Dolby cinema sound three decades ago, now you know how the system worked.

The film featured also had an analogue soundtrack, and if you’d like to know how they worked, we’ve got you covered!

Converting Your Bike To Electric: Why You Should, And When You Shouldn’t

March 29, 2022 by Jenny List 96 Comments

A decade ago I was lucky enough to work for an employer that offered a bicycle loan scheme to its employees, and I took the opportunity to spend on a Brompton folding bike. This London-made machine is probably one of the more efficiently folding cycles on the market, and has the useful feature of being practical for longer journeys rather than just a quick run from the train. A 3-speed hub gearbox is fine for unhurried touring, but sadly my little folder has always been a bit of a pain on the hills. Thus around the start of the pandemic I splashed out again and bought a Swytch electric upgrade kit for it, and after a few logistical and life upheavals I’ve finally fitted it to the bike. I’ve ridden a few electric bikes but never had my own, so it’s time to sit down and analyse the experience. Is an electric bike something you should have, or not?

A Box Of Bits Becomes An Electric Bike

All the parts of a Swytch kit. From the Swytch assembly manual.

Swytch sell their kits via crowdfunding rounds, so I’d been on a waiting list for a while and got an early-bird price on my kit. It took quite a while to arrive, much longer than the expected time in mid-2020 because of the pandemic, finally being delivered some time in February last year. It came in a modestly-sized cardboard carton which would be an easy carry on the Brompton’s luggage rack, containing neatly packed a new front wheel with motor, as well as the battery and all sundry parts.

Fitting the kit shouldn’t stretch the capabilities of a Hackaday reader, with probably the trickiest part being the positioning of a Hall-effect sensor near the crank. The kit works by providing a motor assist when you pedal, so part of it is a set of magnets on a plastic disk with various attachments for different cranks and pedal sets. The Brompton front wheel is removed and its tyre and tube transferred to the Swytch one, which is then put on the bike. Once the magnet disk and Hall sensor are attached, the cables follow the existing ones and emerge at the handlebars where a sturdy bracket for the battery box is fitted. Continue reading “Converting Your Bike To Electric: Why You Should, And When You Shouldn’t” →

DIY SLS 3D Printer Getting Ready To Print

March 25, 2022 by Dave Rowntree 12 Comments

Ten years ago the concept of having on our desks an affordable 3D printer knocking out high quality reproducible prints, with sub-mm accuracy, in a wide range of colours and material properties would be the would be just a dream. But now, it is reality. The machines that are now so ubiquitous for us hackers, are largely operating with the FDM principle of shooting molten plastic out of a moving nozzle, but they’re not the only game in town. A technique that has also being around for donkeys’ years is SLS or Selective Laser Sintering, but machines of this type are big, heavy and expensive. However, getting one of those in your own ‘shop now is looking a little less like a dream and more of a reality, with the SLS4All project by [Tomas Starek] over on hackaday.io.

[Tomas] has been busy over the past year, working on the design of his machine and is now almost done with the building and testing of the hardware side. SLS printing works by using a roller to transfer a layer of powdered material over the print surface, and then steering a medium-power laser beam over the surface in order to heat and bond the powder grains into a solid mass. Then, the bed is lowered a little, and the process repeats. Heating of the bed, powder and surrounding air is critical, as is moisture control, plus keeping that laser beam shape consistent over the full bed area is a bit tricky as well. These are all hurdles [Tomas] has to overcome, but the test machine is completed and is in a good place to start this process control optimisation fun. Continue reading “DIY SLS 3D Printer Getting Ready To Print” →

A MiniDisc Optical Head Has A Few Surprises Up Its Sleeve

March 24, 2022 by Jenny List 46 Comments

There was an odd era at the start of the 1990s when CDs had taken the lead from vinyl in pre-recorded music, but for consumer recordable formats the analogue cassette was still king. A variety of digital formats came to market to address this, of which Sony’s MiniDisc was the only one to gain significant traction outside the studio. These floppy-disk-like cartridges held a magneto-optical medium , and were the last word in cool until being swept away around the end of the decade by MP3 players. Hackaday alum [Nava Whitford] has disassembled a MiniDisc optical head to document how the physical part of the system worked.

The first surprise is that the MiniDisc was in fact a two-in-one system. The recordable discs were magneto-optical and wrote data by heating the disc with a laser under a magnetic field, while the pre-recorded discs used etched pits and lands in a similar way to the CD. Remembering the technical buzz around the system back in the day, either we audio enthusiasts glossed over this detail, or more likely, Sony’s PR did so to emphasize the all-new aspect of the system.

The teardown goes in depth into how while like a CD player there is a photodiode array involved, the extra components are a diffraction grating and a Wollaston prism, an optical component which splits polarized light into two beams. The photodiode array is more complex than that of a CD player, it’s speculated that this is to detect the different polarized beams as well as for the task of maintaining alignment with the track.

All in all this is a rare chance to look at something we know, but which few of us will probably have dismantled due to its relative scarcity compared to CD mechanisms. Definitely worth a look. Meanwhile if this era is of interest, take a look at a Hack Chat we did a while back looking at the MiniDisc’s would-be competitor.

3D Printing Concept Car (Parts)

March 23, 2022 by Al Williams 6 Comments

When you want to fabricate something you either start with something and take away what you don’t want — subtractive manufacturing — or you start with nothing and add material, which is additive manufacturing that we usually call 3D printing. Popular Science recently took a look inside Vital Auto, the British lab that uses 3D printing for high-end concept cars from companies like Rolls-Royce, McLauren, Jaguar, and others. In the video below, [Anthony Barnicott], an engineer for Vital, says that the two technologies — additive and subtractive — work best when used together.

As you might expect, they are not using a $200 FDM printer. They have three Formlabs 3Ls that print with resin and five Formlab Fuse 1 selective laser sintering printers. While metal printers are still uncommon in hacker’s workshops, resin printers are now very affordable although your garage printer is probably a good bit smaller than the 3L’s 335x200x300 mm volume. For comparison, an LCD-based AnyCubic Photon X provides just 165x132x80 mm. Of course, you’re looking at about $11,000 for the dual-laser 3L versus about $240 for the Photon.

Vital started building the EP9 electric car concept for NIO, an electric car maker in China. You can imagine that modern manufacturing machines make it possible to create more sophisticated concept cars faster. How many times do you want to tweak a part that takes a machinist eight hours to produce? But if you can just let a machine run overnight and get the result in the morning, you are more likely to change and refine the part.

Vital Auto is an interesting look at how professional fabrication shops are using the same technologies we do, at least at the core. We’ve noted before how these same technologies are making homebrew projects look better than some commercial products not long ago. You can print big things if you break them up, of course. Or, break the bank and buy a really big printer.

Continue reading “3D Printing Concept Car (Parts)” →

Cluster Your Pi Zeros In Style With 3D Printed Cray-1

March 21, 2022 by Tom Nardi 36 Comments

From a performance standpoint we know building a homebrew Raspberry Pi cluster doesn’t make a lot of sense, as even a fairly run of the mill desktop x86 machine is sure to run circles around it. That said, there’s an argument to be made that rigging up a dozen little Linux boards gives you a compact and affordable playground to experiment with things like parallel computing and load balancing. Is it a perfect argument? Not really. But if you’re anything like us, the whole thing starts making a lot more sense when you realize your cluster of Pi Zeros can be built to look like the iconic Cray-1 supercomputer.

This clever 3D printed enclosure comes from [Kevin McAleer], who says he was looking to learn more about deploying software using Ansible, Docker, Flask, and other modern frameworks with fancy sounding names. After somehow managing to purchase a dozen Raspberry Pi Zero 2s, he needed a way to keep them all in a tidy package. Beyond looking fantastically cool, the symmetrical design of the Cray-1 allowed him to design his miniature version in such a way that each individual wedge is made up of the same identical set of 3D printed parts.

In the video after the break, [Kevin] explains some of the variations the design went through. We appreciate his initial goal of making it so you didn’t need any additional hardware to assemble the thing, but in the end you’ll need to pick up some M2.5 standoffs and matching screws if you want to build one yourself. We particularly like how you can hide all the USB power cables inside the lower “cushion” area with the help of some 90-degree cables, leaving the center core open.

This isn’t the first time we’ve seen somebody build their own tiny Cray-1. A particularly dedicated hacker built his own 1/10th scale replica of the 1970s supercomputer powered by an FPGA back in 2010, and eventually got to the point of trying to boot original software on it.

Continue reading “Cluster Your Pi Zeros In Style With 3D Printed Cray-1” →

ElectronBot: A Sweet Mini Desktop Robot That Ticks All The Boxes

March 20, 2022 by Dave Rowntree 12 Comments

[Peng Zhihui] seems to have found some spare time and energy to crack out another sweet robot build, this time it’s a much smaller, and cuter emoji-bot (Original GitHub Link,) with the usual production-ready levels of attention to detail. With a lot of fine details in the 3D printed models, this is one for SLS printing in nylon, but that can be done for a reasonable outlay, in China at least. The electronics package consists of a few full custom, and tiny, PCBs designed with Altium Designer, with off-the-shelf modules for the circular LCD and camera. The main board hosts an STM32F405 and deals with the display and SD card, The reason for this choice of STM32 was due to the requirement for connecting to an external USB3300 high-speed USB PHY. There is a sensor PCB which handles the gesture sensor, a USB hub, MPU6050 9-axis sensor, and also the USB camera module. This board attaches to the USB-C connector in the base, via a FFC cable, allowing the robot to rotate on its base.

[Peng] clearly has exacting standards as to how things should work, and we guess wanted to have the arms back-driveable in a way that enabled the host computer to track and record the motor positions for replaying later on. The connection back to the controller is via I²C, allowing all five servos to hang on the same bus, saving previous resources. Smart! Getting a processor and motor driver in such a tiny space was a bit of challenge, but a walk in the park for [Peng] as is demonstrates in the video embedded below (We believe English subtitles are pending!) The arm mechanism is particularly interesting, and rather elegantly executed, and he does seem rather proud of this part of the design, and so he should! Like with [Peng’s] other projects, there is a lot to see, and plenty of scope for feature explosion. It was nice to see the ‘bot being used as an input device, not only with gesture sensing via the dedicated sensor, but also using the camera with OpenCV to track user posture and act accordingly. This thing could act as genuinely useful AI device, as was a being darn cute at the same time!

We know you come to Hackaday for your cute robot fix, and we’re not going to disappoint. Here’s a cute robot lamp, an obligatory spot (a robot dog) type project, and if you’re more of a cat person, then we got that base covered as well.

Continue reading “ElectronBot: A Sweet Mini Desktop Robot That Ticks All The Boxes” →