Build Yourself A Vacuum Tube VU Meter

March 22, 2024 by Lewin Day 5 Comments

Volume unit (VU) meters are cool — it’s an undeniable fact. For some reason, humans just dig lights that flash along with sounds. You can build a VU meter using LEDs, or bulbs if you’re trapped in 1972. Or, you could use special vacuum tubes. [mircemk] did just that in their latest VU meter project.

The 6E2 vacuum tube is the part for the job in this case. You might think a specialist tube like this is expensive, but they can be had for just a few dollars from online retailers. They were often used as tuning indicators, but here, they’re used as a responsive VU meter instead. However, instead of a single bar going up and down, you get a pair of bars that raise to meet in the middle.

[mircemk] explains all the circuitry required to drive the tubes, and how to hook them up to create a two-channel stereo VU meter. The final circuit largely relies on a transistor, a diode, some passive components, and a DC-DC boost supply to generate 250 V for the tubes.

The final result looks pretty neat, particularly as it’s built into an old-school blue project box. We’ve seen similar projects from [mircemk] before, too. Continue reading “Build Yourself A Vacuum Tube VU Meter” →

Modern Microcontroller Boosts Classic Logic Analyzer To New Heights

March 19, 2024 by Lewin Day 5 Comments

[Ted Fried] recently found a beautiful HP 1600A/1607A logic analyzer set. State of the art in 1975, it looks like glorious Space Age equipment today. He decided to hook it up some modern gear to put it through its paces.

Wanting to give the equipment a proper shakedown, he enlisted a Teensy 4.1 to spit a deluge of logic at the HP unit. The microcontroller was tasked with generating 32 data signals along with two clock outputs to give the analyzer plenty to analyze. The HP 1600A handled this no problem, so [Ted] kept tinkering.

His next feat was to explore the addressable “MAP” function of the unit, which allowed writing to the 64×64 pixel display. The Teensy 4.1 was easily able to send images to the display, but [Ted] isn’t stopping there. He’s got plans to do the usual thing and get Bad Apple going on the hardware.

Getting a logic analyzer to analyze logic isn’t much of a hack, sure. But it’s instructive of how to approach working with such hardware. If you want to spit a bunch of logic out fast, a Teensy 4.1 is a great choice because it’s got a ton of IO and a ton of clock cycles to tickle it with.

We enjoyed seeing this old piece of hardware light up the phosphors once more. If you’ve got your own projects going on with classic bits of HP test gear, don’t hesitate to let us know!

STM32 Draws On Scope

March 10, 2024 by Al Williams 7 Comments

Drawing on an oscilloscope’s XY mode isn’t a new idea. However, if you’ve ever wanted to give it a go, you’d be hard-pressed to find more information than the nearly hour-and-a-half video about the topic from [Low Byte Productions]. You can check out the video below.

If you prefer to jump straight into the code, there’s a GitHub page. While the code is specific to the STM32, you can apply the ideas to anything.

Continue reading “STM32 Draws On Scope” →

Dial-Up Is Still, Just Barely, A Thing

March 6, 2024 by Lewin Day 97 Comments

In an era dominated by broadband and wireless cellular networks, it might come as a surprise to many that dial-up internet services still exist in the United States. This persistence is not a mere relic of nostalgia — but a testament to the diverse and uneven nature of internet infrastructure across the country.

Yes, dial-up internet, with those screechy, crackly tones, remains a useful tool in areas where modern, high-speed internet services are either unaffordable or unavailable. Subscriber numbers are tiny, but some plough on and access the Internet by the old ways, not the new.

Continue reading “Dial-Up Is Still, Just Barely, A Thing” →

Making A Crystodyne Radio With Zinc Oxide And Cat’s Whiskers

March 5, 2024 by Maya Posch 19 Comments

Zinc negative resistance oscillator circuit. (Credit: Ashish Derhgawen)

During the first half of the 20th century radio technology was booming, albeit restricted by the vacuum tube technology of the time which made radios cumbersome in size and power needs. The development of a solid state alternative to the vacuum tube was in full swing, but the first version pioneered by [Oleg Losev] in the form of crystal radios failed to compete. Even so these ‘crystal radios’ laid much of the groundwork for subsequent research. The ease of creating this type of radio also makes it a fun physics experiment today, as [Ashish Derhgawen] demonstrates in a blog post.

In the January 1925 issue of Radio News the theory of the circuit is explained by [Oleg Losev] himself (page 1167). At the core is a material capable of negative resistance, as a non-linear (non-Ohmic) material, which means that the current passing through them decreases as voltage increases over part of their I-V curve. This enables it to work as an amplifier or oscillator. After the cessation of research on crystal radio technology by [Losev] and others, the negative resistance diode was rediscovered in 1957 with the tunnel diode.

Continue reading “Making A Crystodyne Radio With Zinc Oxide And Cat’s Whiskers” →

A Better Use For The AGP Slot, Decades Later

March 3, 2024 by Jenny List 25 Comments

For a while around a quarter century ago PC motherboards came with a special slot, a little shorter than the PCI slots which ruled the roost back then, and offset from them further into the case. This was the Accelerated Graphics Port, or AGP, a standard created to more quickly serve the 3D graphics cards which were then taking the world by storm. It was everywhere for a few years, then in the mid-2000s it was replaced by PCI Express and faded into obscurity. [Peter] has a Socket 7-based NAS with an AGP slot, and was left wondering whether the unused port could be put to a worthwhile purpose.

AGP is a superset of PCI clocked at 66 MHz, and usually benefiting from having its own exclusive bridge to the processor bus. Thus he reasoned that he could make an AGP to PCI adapter and it might work, as the right connections are all there. A hacked-together version was made by butchering two riser cards, and when a network card worked quite happily he knew he was on to something and made a PCB. There’s a caveat that it only works with 66-MHz capable PCI cards so not everything will work, but if you’re one of the very few people who must be in the market for one, he can do you a PCB.

We’d normally end with a link to a related project here, but we must instead congratulate [Peter]. As far as we can find, this is Hackaday’s first AGP hack, two decades later. Continue reading “A Better Use For The AGP Slot, Decades Later” →