Convert A Cheap Tube Preamp Into A Headphone Amp With Jenny

February 27, 2025 by 21 Comments

Big-name tube amplifiers often don’t come cheap. Being the preserve of dedicated audiophiles, those delicate hi-fis put their glass components on show to tell you just how pricy they really ought to be. If you just want to dip your toe in the tube world, though, there’s a cheaper and more accessible way to get started. [Jenny List] shows us the way with her neat headphone amp build.

The build starts with an off-the-shelf preamp kit based around two common 6J1 tubes. These Chinese pentode valves come cheap and you can usually get yours hands on this kit for $10 or so. You can use the kit as-is if you just want a pre-amp, but it’s not suitable for headphone use out of the box due to its high-impedance output. That’s where [Jenny] steps in.

You can turn these kits into a pleasing headphone amp with the addition of a few choice components. As per the schematic on Github, a cheap transformer and a handful of passives will get it in the “good enough” range to work. The transformer isn’t perfect, and bass response is a compromise, but it’s a place to start your tinkering journey. Future work from [Jenny] will demonstrate using a MOSFET follower to achieve much the same result.

We’ve seen a great number of headphone amplifiers over the years, including one particularly attractive resin-encased example. Video after the break.

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Automatic Pill Dispenser Is Cheap And Convenient

February 12, 2025 by 20 Comments

If you’re taking any medication, you probably need to take it in a certain dose on a certain schedule. It can quickly become difficult to keep track of when you’re taking multiple medications. To that end, [Mellow_Labs] built an automated pill dispenser to deliver the right pills on time, every time.

The pill dispenser is constructed out of 3D printed components. As shown, it has two main bins for handling two types of pills, controlled with N20 gear motors. The bins spin until a pill drops through a slot into the bottom of the unit, with the drop detected by a piezo sensor. It uses a Beetle ESP32 as the brains of the operation, which is hooked up with a DS1307 real-time clock to ensure it’s dosing out pills at the right time. It’s also wired up with a DRV8833 motor driver to allow it to run the gear motors. The DRV8833 can run up to four motors in unidirectional operation, so you can easily expand the pill dispenser up to four bins if so desired.

We particularly like how the pill dispenser is actually controlled — [Mellow_Labs] used the ESP32 to host a simple web interface which is used for setting the schedule on which each type of pill should be dispensed.

We’ve featured some other pill dispenser builds before, too.

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Putting Cheap Motorcycle Tachometers To Work

January 18, 2025 by 15 Comments

With so much data being thrown at our eyeballs these days, it’s worryingly easy for the actually important stuff to slip by occasionally. So when [Liam Jackson] wanted a way to visualize the number of test failures popping up in the continuous integration system at work, he went with a novel but effective solution — universal motorcycle tachometers.

It turns out these little gauges can be had for under $10 a piece from the usual overseas retailers, and are very easy to drive with a microcontroller. As [Liam] explains, all you need to do other than providing them with 12 volts, is feed them a PWM signal. Even though the gauges are designed for a 12 V system, they apparently don’t have any problem responding to the 5 V logic level from the Arduino’s pins.

As for the frequency he says that 1,000 RPM corresponds to 16.66 Hz, so you can just multiply up from there to show whatever number you wish. That said, [Liam] warns that the gauges draw several hundred milliamps once the needle gets into the two digit range, so keep that in mind. Conveniently, those number happen to be in red anyway…

For his particular application, [Liam] put three of the gauges together to create a very handsome dashboard. If you want to recreate his setup exactly he’s made the STLs available for the gauge cluster housing. Note the small OLED at the center, this offers a way to show a bit more context than the three analog gauges alone can express, especially if you’ve got an application where you might be switching between multiple data sources.

Over the years we’ve seen several projects that repurposed analog gauges of various types, often for showing computer performance, but they generally involved having to drive the galvanometers directly. That these tachometers can simply be fed a simple digital signal should make implementing them into your project much easier.

Hackaday Podcast Episode 303: The Cheap Yellow Display, Self-Driving Under $1000, And Don’t Remix That Benchy

January 10, 2025 by 1 Comment

As the holiday party season fades away into memory and we get into the swing of the new year, Elliot Williams is joined on the Hackaday Podcast by Jenny List for a roundup of what’s cool in the world of Hackaday. In the news this week, who read the small print and noticed that Benchy has a non-commercial licence? As the takedown notices for Benchy derivatives fly around, we muse about the different interpretations of open source, and remind listeners to pay attention when they choose how to release their work.

The week gave us enough hacks to get our teeth into, with Elliot descending into the rabbit hole of switch debouncing, and Jenny waxing lyrical over a crystal oscillator. Adding self-driving capability to a 30-year-old Volvo caught our attention too, as did the intriguing Cheap Yellow Display, an ESP32 module that has (almost) everything. Meanwhile in the quick hacks, a chess engine written for a processor architecture implemented entirely in regular expressions impressed us a lot, as did the feat of sending TOSLINK across London over commercial fibre networks. Enjoy the episode, and see you again next week!

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More Things To Do With Your Cheap Yellow Display

January 7, 2025 by 13 Comments

The Cheap Yellow Display (CYD) is an ESP32 development board that’s been making the rounds for a while now, thanks to its value and versatility. For around $10 USD, you get a nicely integrated package that’s perfect for a wide array of projects and applications. Toss a couple in on your next AliExpress order, and all you need to do is come up with an idea. [Craig Lindley] had two ideas, and maybe they will help get those gears turning in your head. Even if you don’t need a network-connected MP3 player or GPS information display, we bet browsing the source code would be useful.

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Is A Cheap Frequency Standard Worth It?

January 6, 2025 by 26 Comments

In the quest for an accurate frequency standard there are many options depending on your budget, but one of the most affordable is an oven controlled crystal oscillator (OCXO). [RF Burns] has a video looking at one of the cheapest of these, a sub ten dollar AliExpress module.

A crystal oven is a simple enough device — essentially just a small box containing a crystal oscillator and a thermostatic heater. By keeping the crystal at a constant temperature it has the aim of removing thermal drift from its output frequency, meaning that once it is calibrated it can be used as a reasonably good frequency standard. The one in question is a 10 MHz part on a small PCB with power supply regulator and frequency trimming voltage potentiometer, and aside from seeing it mounted in an old PSU case we also are treated to an evaluation of its adjustment and calibration.

Back in the day such an oscillator would have been calibrated by generating an audible beat with a broadcast standard such as WWV, but in 2024 he uses an off-air GPS standard to calibrate a counter before measuring the oven crystal. It’s pretty good out of the box, but still a fraction of a Hertz off, thus requiring a small modification to the trimmer circuit. We’d be happy with that.

For the price, we can see that one of these makes sense as a bench standard, and we say this from the standpoint of a recovering frequency standard nut.

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Light Brite Turned Sci-Fi Console On The Cheap

January 2, 2025 by 13 Comments

Generally, the projects featured on Hackaday actually do something. We won’t go as far as to say they are practical creations, but they usually have some kind of function other than to sit there and blink. But what if just sitting still and blinking away randomly is precisely what you want a piece of hardware to do?

That was exactly the goal when [createscifi] set out to dress a Lite Brite up as a futuristic prop. On a technical level, this project is pretty much as simple as it gets. But we appreciated seeing some of the techniques brought to bear on this project, and perhaps more importantly, really like the channel’s overall goal of creating affordable sci-fi props using common components. We don’t plan on filming our own space epic anytime soon…but we like to know the option is there.

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