Author: Jenny List

3362 Articles

A CMOS Ring Modulator Pedal

December 24, 2021 by 9 Comments

Earlier this year, we featured an unusual radio receiver that took the very traditional superhetrodyne design and implemented it in an unexpected fashion without any inductors, using instead a combination of 74HC logic chips and op-amps. Its designer [acidbourbon] remarks that the circuit bears a striking resemblance to a ring modulator,so has taken it down that path by producing a 74HC based ring modulator guitar pedal.

In both circuits, a 74HC4046 phase-locked loop chip serves as an oscillator, driving a 74HC4051 analogue switch chip that performs the mixer task. The extra-op-amp filter and demodulator circuitry from the radio is omitted, and the oscillator frequency moved down to the audio range. The result can be heard in the video, and we probably agree with him that it’s not quite the same as a classic ring modulator. This lies in the type of mixer, the diodes used in a traditional circuit have a forward voltage to overcome before they start or end conducting, while the CMOS switch chip does so immediately on command.

The 4000 series CMOS and their descendants are a fascinating family with many unexpected properties that our colleague Elliot Williams has gone into detail with for his Logic Noise series. Meanwhile take a look at our coverage of the original radio.

Continue reading “A CMOS Ring Modulator Pedal” →

Know Audio: Mixtapes, Tape Loops, And Razor Blades

December 20, 2021 by 16 Comments

In our no-nonsense journey through the world of audio technology we’ve so far have looked at digital audio and the vinyl disk recording. What’s missing? Magnetic tape, the once-ubiquitous recording medium that first revolutionised the broadcast and recording industries in the mid-20th-century, and went on to be a mainstay of home audio before spawning the entire field of personal audio. Unless you’re an enthusiast or collector, it’s likely you won’t have a tape deck in your audio setup here in 2021 and you’ll probably be loading your 8-bit games from SD card rather than cassette, but surprisingly there are still plenty of audio cassettes released as novelties or ephemeral collectables.

The Device That Made The Sound Of The Latter Half Of The 20th Century

"Like a travelling razor blade", a Blattnerphone steel-strip tape recorder at the BBC in 1937. Douglas Hallam, Jr., Public domain.
“Like a travelling razor blade”, a Blattnerphone steel-strip tape recorder at the BBC in 1937. Douglas Hallam, Jr., Public domain.

The first magnetic recordings were made directly on metal wires, but metal fatigues as it bends. By coating a flexible plastic tape in ferrous particles, the same simple technique of laying down an audio signal as variations in the magnetic field could be made smaller, lighter, and more robust. But the key to the format’s runaway success is the technical advancements that differentiate those 1950s machines from their wire recorder ancestors.

Whether it is a humble cassette recorder or a top-end studio multitrack, all tape recorders are very similar. There are two reels that hold the tape: the playback reel that houses the recording, and the take-up reel that stores the tape as it plays in the machine. The take-up reel is lightly driven to run faster than the tape speed, and the playback reel has a slight braking force to keep the tape under tension at all times. Continue reading “Know Audio: Mixtapes, Tape Loops, And Razor Blades” →

An All In One Cube PC For A 1990s That Never Quite Happened

December 20, 2021 by 12 Comments

When a particular device or appliance is evoked, there comes with it a set of expectations over what it might look like. A toaster, a camera, a washing machine, or a PC, will all have their own accepted form factors, and it’s rare that a manufacturer is adventurous enough to venture outside them. In the world of PCs there was a brief flowering of this type of creativity through the 1990s, and it’s that time which [ikeji]’s cube PC squarely fits in. It’s a 3D printed PC with a built-in display, keyboard, and printer, and while some might categorize it as a cyberdeck we’d say it goes further, we could easily imagine a slightly more polished version being an object of desire back when a powerful machine carried an 80486.

Inside it’s no slouch, packing an AMD Ryzen 7 Pro on a Mini-ITX motherboard, and while the display is a mere 7-incher it fits neatly behind the fold-down keyboard. The thermal printer is maybe more of a toy, but it’s good to find that even a bleeding-edge motherboard still has a serial port on it somewhere that it can talk to.

While the build undoubtedly has a few home-built rough edges we like the idea, echoing as it does those all-in-ones from the CRT era. Unless you have a handy Minitel terminal you won’t find much like it.

A Particularly Festive Chip Decapping

December 20, 2021 by 16 Comments

As we approach the moment in the year at which websites enter a festive silly season of scrambling to find any story with a festive angle, we’re pleased to see the ever-reliable [Ken Shirriff] has brought his own take on Christmas tech to the table with a decapping of the UM66T melody chip that has graced so many musical greeting cards.

The surprise in this age of ubiquitous microcontrollers is that this is not a smart device; instead it’s a single-purpose logic chip whose purpose is to step through a small ROM containing note values and durations, driving a frequency generator to produce the notes themselves. The frequency generator isn’t the divider chain from the RC oscillator that we might expect, instead it’s a shift register arrangement which saves on the transistor count.

Although the UM66 is a three-pin device, there are a few other pins on the die. These are likely to be for testing. As a 30+ year old product its design may be outdated in 2021, but it’s one of those chips that has survived without being superseded because it does its task without the need for improvement. So when you open a card and hear the tinny tones of a piezo speaker this holiday season, spare a thought for the ingenuity of the design behind the chip that makes it all possible.

When Does Car Hacking Become “Tampering”? The British Government Seeks Guidance

December 18, 2021 by 87 Comments

When a government decides to take a look at your particular field of experimentation, it’s never necessarily a cause for rejoicing, as British motor vehicle enthusiasts are finding out through a UK Government consultation. Titled “Future of transport regulatory review: modernising vehicle standards“, the document explains that it is part of the process of re-adopting under UK law areas which have previously been governed by the European Union. Of particular interest is the section “Tackling tampering”, which promises a new set of offences for “tampering with a system, part or component of a vehicle intended or adapted to be used on a road“.

They go into detail as to the nature of the offences, which seem to relate to the production of devices designed to negate the safety or environmental features of the car. They’re at pains to say that they have no wish to target the legitimate car modification world, for example in motorsport or restoration, but it’s easy to see how a car hacker might inadvertently fall foul of any new rules. It’s worried the enthusiasts enough that a petition has been launched on the UK parliamentary petition site, making the point that the existing yearly MOT roadworthiness test should fulfill the function of taking any illegal vehicles off the road.

We’re always wary when governments wander into our purview, and given where this is being written it’s fair to say that British governments have had their fair share of ill-considered laws in their time. But before we call doom upon the future of car hacking for Brits, it’s worth remarking that they don’t always make a mess in this arena. The rules for the Individual Vehicle Approval test for putting a home-built car on the road are far from a bureaucratic nightmare for example, instead being a relatively sensible primer in building a safe motor vehicle.

So we’d suggest not to panic just yet, but perhaps any British readers might like to respond appropriately to the consultation and the petition in the interests of nudging them in the right direction.

Thanks [Adam Quantrill] for the tip.

The Seductive Pull Of An Obsolete Home Movie Format

December 15, 2021 by 53 Comments

It’s dangerous for a hardware hacker to go into a second-hand store. I was looking for a bed frame for my new apartment, but of course I spent an age browsing all the other rubbish treasures on offer. I have a rough rule of thumb: if it’s not under a tenner and fits in one hand, then it has to be exceptional for me to buy it, so I passed up on a nice Grundig reel-to-reel from the 1960s and instead came away with a folding Palm Pilot keyboard and a Fuji 8mm home movie camera after I’d arranged delivery for the bed. On those two I’d spent little more than a fiver, so I’m good. The keyboard is a serial device that’s a project for a rainy day, but the camera is something else. I’ve been keeping an eye out for one to use for a Raspberry Pi camera conversion, and this one seemed ideal. But once I examined it more closely, I was drawn into an unexpected train of research that shed some light on what must of been real objects of desire for my parents generation.

A Thrift Store Find Opens A Whole New Field

One f the surprises comes in just how small this thing is.
One of the surprises comes in just how small this thing is.

The Fuji P300 from 1972 is typical among consumer movie cameras of the day. It takes the form of a film magazine with a zoom lens assembly on its front, a reflex viewfinder on its side, and a handle with a shutter trigger button on it protruding vertically below the magazine and also housing the batteries.

Surprisingly it still has a mercury cell that would have powered its light meter; a minor annoyance to dispose of this correctly. Sometimes these devices had clockwork motors, but this one has an electric motor. It also has a light sensor that is coupled to some kind of electromechanical aperture. It would have been an expensive camera when it was new, probably as much of a purchase as an SLR or a decent mirrorless camera here in 2021.

The surprise came when I opened it up, for it looked like no other 8mm camera I had seen. I’m familiar wit the two reels of a Standard 8 or the boxy cassette of Super 8, but this one used something different. That film magazine is made to fit a compact twin-reel cartridge whose film fits in a metal film gate. This is a Single 8 camera, Fuji’s entry in the all-in-one 8 mm film market, and a format I never knew existed. To explain my unexpected discovery it was necessary to delve into the world of home movie formats in the decade before videotape arrived and drove them out. Continue reading “The Seductive Pull Of An Obsolete Home Movie Format” →

You Can Always Use An ATtiny Instead Of A 555

December 15, 2021 by 62 Comments

It’s a constant of writing for Hackaday, that whenever a project appears using a 555 timer, someone will say “You could have used a microcontroller to do that!”. It’s something that [Shranav Palakurthi] has approached with the ATTiny555, a project that emulates an entire 555 by making clever use of the humble and ubiquitous microcontroller chip. We’ve all been guilty of it at some time, but now at last the ATTiny85 enthusiasts have conclusive proof that their favourite piece of cheap silicon can prove its mettle.

The full details of the ingenious 555 replacement can be found in its GitHub repository, and for those willing to take the plunge it’s as simple as adding a resistor and updating the firmware. It’s not the perfect 555 replacement with its imperfect analogue performance and swapped reset and ground pins, but it does however bring the advantage of a lower supply voltage.

You can see the device in action in the YouTube video below the break, but meanwhile rejoice that finally there’s a way to replace all those unnecessary 555s with your favourite inexpensive 8-pin chip!

While we’re on the subject of the 555, don’t forget we’re running our 555 contest again.

Continue reading “You Can Always Use An ATtiny Instead Of A 555” →