The Open-Source Multimeter: The HydraMeter

Designing An Open Source Multimeter: The HydraMeter

July 20, 2025 by 16 Comments

Our hacker [John Duffy] wrote in to let us know about a video he put together to explain the design of his open-source multimeter, the HydraMeter.

If you’re interested in how the circuitry for a voltmeter, ohmmeter, or ammeter might work, this video is a masterclass. In this long and detailed video, [John] walks us through his solutions to various challenges he had while designing his own multimeter. We covered this multimeter last year, and this new video elaborates on the design of the HydraMeter which has been a work in progress for years now.

The basic design feeds voltage, current, and resistance front-ends into an Analog to Digital Converter (ADC), which then feeds into a microcontroller and out to the (detachable) display. You can find the KiCad design files on the GitHub page. There is also a write-up on hackaday.io.

The user interface for the meter is… opinionated, and perhaps not to everyone’s taste. In the video, [John] talks a little bit about why he made the UI work the way that it does, and he noted that adding a rotary range switch is a goal for version 2.0.

Thank you, [John], for putting this video together; it is an excellent resource. We look forward to seeing version 2.0 develop soon!

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When A Record Player Doesn’t Work Due To Solid State Grease

July 20, 2025 by 24 Comments

Normally, mechanical devices like record players move smoothly, with well-greased contact surfaces enabling the tone arm to automatically move, the multi-record mechanism to drop down a fresh disc, and the listener to have a generally good time. Unfortunately, the 1972-era ITT KP821 record player that [Mark] got recently handed by a friend wasn’t doing a lot of moving, with every part of the mechanism seemingly frozen in place, though the current owner wasn’t certain that they were doing something wrong.

Fortunately, this record player was in exceptionally good condition.. The primary failure was that the BSR record player mechanism, with its many touching metal surfaces, was suffering from a bad case of solidified grease. Although this is easily fixed with some IPA and a lot of elbow grease, the biggest trick with these mechanisms is putting it back together after cleaning, with many seemingly randomly shaped parts and every single E-clip that the manufacturer could design for and source at the time.

With that complete, this just left some pot cleaning and replacing a busted fuse in the amplifier section. The selenium rectifier was still functional, as were the SGS TAA621AX1 audio amplifier ICs. Despite the age of this ‘portable’ record player, both its BSR mechanism and the twin speakers that are part of the record player are in remarkably good condition. Much like with a car, it seems that you just have to swap out the liquid-y elements before they turn into a solid.

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8 Bit Mechanical Computer Built From Knex

July 20, 2025 by 23 Comments

Long before electricity was a common household utility, humanity had been building machines to do many tasks that we’d now just strap a motor or set of batteries onto and think nothing of it. Transportation, manufacturing, agriculture, and essentially everything had non-electric analogs, and perhaps surprisingly, there were mechanical computers as well. Electronics-based computers are far superior in essentially every way, but the aesthetics of a mechanical computer are still unmatched, like this 8-bit machine built from K’nex.

More after the break…

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Engine Data Displayed Live On Dash

July 20, 2025 by 10 Comments

In the auto world, there are lots of overarching standards that all automakers comply with. There are also lots of proprietary technologies that each automaker creates and uses for its own benefit. [Shehriyar Qureshi] has recently been diving into Suzuki’s Serial Data Line standard, and has created a digital dash using the data gained.

The project started with Python-based scanner code designed to decode Suzuki’s SDL protocol. Armed with the ability to read the protocol, [Shehriyar] wanted to be able to do so without having to haul a laptop around in the car. Thus, the project was ported to Rust, or “oxidized” if you will.

More after the break…

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Project Scribe thermal printer printing out a receipt

Project Scribe: Receipts For Life

July 20, 2025 by 15 Comments

Here’s a fun project. Over on their YouTube page [Urban Circles] introduces Project Scribe.

The idea behind this project is that you can print out little life “receipts”. Notes, jokes, thoughts, anecdotes, memories. These little paper mementos have a physical reality that goes beyond their informational content. You can cut them up, organize them, scribble on them, highlight them, stick them on the wall, or in a scrapbook. The whole idea of the project is to help you make easier and better decisions every day by nudging you in the direction of being more mindful of where you’ve been and where you’re going.

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A long, rectangular electronic device is shown in front of a book of colour swatches. A small LCD display on the electronic device says “PANTONE 3005 C,” with additional color information given in smaller font below this.

A Spectrophotometer Jailbreak To Resolve Colorful Disputes

July 19, 2025 by 22 Comments

The human eye’s color perception is notoriously variable (see, for example, the famous dress), which makes it difficult to standardize colours. This is where spectrophotometers come in: they measure colours reliably and repeatably, and can match them against a library of standard colors. Unfortunately, they tend to be expensive, so when Hackaday’s own [Adam Zeloof] ran across two astonishingly cheap X-Rite/Pantone RM200 spectrophotometers on eBay, he took the chance that they might still be working.

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One ROM to rule them all.

Software Defined Retro ROMs

July 19, 2025 by 6 Comments

Here’s something fun from our hacker [Piers]: Software Defined ROMs.

In this series of three videos, [Piers] runs us through what a software defined ROM is, how to make them, and then how to use them.

As [Piers] explains, one frustration a retro technician will face is a failed ROM chip. In the era he’s interested in, there are basically three relevant kinds of ROM chip, all 24-pin Dual Inline Package (DIP):

  • 2364 ROM chip: 8KB; 1x chip-select line
  • 2332 ROM chip: 4KB; 2x chip-select lines
  • 2316 ROM chip: 2KB; 3x chip-select lines

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