Follow The Bouncing Needles Of This Analog Meter Clock

Our community never seems to tire of clock builds. There are seemingly infinite ways to mark the passage of time, and finding unique ways to display it is endlessly fascinating.

There’s something about this analog voltmeter clock that really seems to have caught on with the Redditors who commented on the r/DIY thread where we first spotted this. [ElegantAlchemist]’s design is very simple – just a trio of moving coil meters with nice industrial-looking bezels. The meters were wired for 300 volts AC, so the rectifier and smoothing cap were removed and the series resistance was substituted for one more appropriate for the 0-5VDC range needed for the project. New dial faces showing hours, minutes and seconds were whipped up in Corel Draw, and everything was put into a sturdy and colorful aluminum “stomp box” normally used for effects pedals. An Arduino Nano and an RTC drive the meters with a nice, bouncy action. Simple, cheap to build, and a real crowd pleaser.

The observant reader will note a similarity to a clock we covered a while back. That one chose 3D-printed cases for an airplane instrument cluster look. We like the spare case design in [ElegantAlchemist]’s build, but wonder how this clock would look in a fine wood case.

DIY Ribbon Element Upgrades A Studio Microphone

For those with some experience with pro audio, the term “ribbon microphone” tends to conjure up an image of one of those big, chunky mics from the Golden Age of radio, the kind adorned with the station’s callsign and crooned into by the latest heartthrob dreamboat singer. This DIY ribbon mic is none of those things, but it’s still really cool.

Of course the ribbon mic isn’t always huge, and the technology behind it is far from obsolete. [Frank Olsen]’s ribbon mic starts out with gutting a run-of-the-mill studio mic of its element, leaving only the body and connector behind. The element that he constructs, mostly from small scraps of aluminum and blocks of acrylic, looks very much like the ribbon element in commercial mics: a pair of magnets with a thin, corrugated strip of foil suspended between them. The foil was corrugated by passing it through a jig that [Frank] built, which is a neat tool, but he says that a paper crimper used for crafting would work too. There’s some pretty fussy work behind the cartridge build, but everything went together and fit nicely in the old mic body. The video below was narrated using the mic, so we know it works.

Fun fact: the ribbon microphone was invented by Walter Schottky. That Walter Schottky. Need more on how these mics work? Our colleague [Al Williams] has you covered with this article on the basics.

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Old Wattmeter Uses Magnetics To Do the Math

Measuring power transfer through a circuit seems a simple task. Measure the current and voltage, do a little math courtesy of [Joule] and [Ohm], and you’ve got your answer. But what if you want to design an instrument that does the math automatically? And what if you had to do this strictly electromechanically?

That’s the question [Shahriar] tackles in his teardown of an old lab-grade wattmeter. The video is somewhat of a departure for him, honestly; we’re used to seeing instruments come across his bench that would punch a seven-figure hole in one’s wallet if acquired new. These wattmeters are from Weston Instruments and are beautiful examples of sturdy, mid-century industrial design, and seem to have been in service until at least 2013. The heavy bakelite cases and sturdy binding posts for current and voltage inputs make it seem like the meters could laugh off a tumble to the floor.

But as [Shahriar] discovers upon teardown of a sacrificial meter, the electromechanical movement behind the instrument is quite delicate. The wattmeter uses a moving coil meter much like any other panel meter, but replaces the permanent magnet stator with a pair of coils. The voltage binding posts are connected to the fine wire of the moving coil through a series resistance, while the current is passed through the heavier windings of the stator coils. The two magnetic fields act together, multiplying the voltage by the current, and deflect a needle against a spring preload to indicate the power. It’s quite clever, and the inner workings are a joy to behold.

We just love looking inside old electronics, and moving coil meters especially. They’re great gadgets, and fun to repurpose, too.

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The VU Meter and How It Got That Way

Given its appearance in one form or another in all but the cheapest audio gear produced in the last 70 years or so, you’d be forgiven for thinking that the ubiquitous VU meter is just one of those electronic add-ons that’s more a result of marketing than engineering. After all, the seemingly arbitrary scale and the vague “volume units” label makes it seem like something a manufacturer would slap on a device just to make it look good. And while that no doubt happens, it turns out that the concept of a VU meter and its execution has some serious engineering behind that belies the really simple question it seeks to answer: How loud is this audio signal?

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Analog Meters Become a Clock for Father’s Day

Around Father’s Day each year, we usually see a small spate of dad-oriented projects. Some are projects by dads or granddads for the kids, while others are gifts for the big guy. This analog meter clock fits the latter category, with the extra bonus of recognizing and honoring the influence [Micheal Teeuw]’s father had on him with all things technological.

[Michael] had been mulling over a voltmeter clock, where hours, minutes and seconds are displayed on moving coil meters, for a while.  A trio of analog meters from Ali Express would lend just the right look to the project, but being 200-volt AC meters, they required a little modification. [Michael] removed the rectifying diode and filtering capacitor inside the movement, and replaced the current-limiting resistor with a smaller value to get 5 volts full-range deflection on the meters. Adobe Illustrator helped with replacing the original scales with time scales, and LEDs were added to the meters for backlighting. A TinyRTC keeps time and generates the three PWM signals to drive the meters. Each meter is mounted in its own 3D-printed case, the three of which are linked together into one sleek console. We love the look, which reminds us of an instrument cluster in an airplane cockpit.

Bravo to [Michael’s Dad] for getting his son into the tinkering arts, and cheers to [Michael] on the nice build. We like seeing new uses for old meters, like these server performance monitoring meters.

[via r/DIY]

The Worst Piece Of Test Equipment You’ve Got To Try Hacking

A brand new meter in its blister pack
A brand new meter in its blister pack

I have a fascination with the various online vendors of electronics and other manufactured goods from China. Here are listed the latest wonders from Shenzhen or wherever, which you can have for a surprisingly reasonable price, with the mild inconvenience of a three week wait for the postage.

A particular pastime of mine is to look for the bottom end of the market. Once I’ve picked up the items I came to order I’ll trawl around with the search with low price first and see what can be had for a few dollars. Yes, I take a delight in finding absolute trash, because just sometimes that way you can find a diamond in the rough.

So when I was shopping for a multimeter recently I took a quick look to see what the cheapest model from that particular supplier was. For somewhere around £2.50 or just over $3, I could have a little pocket analogue multimeter, the kind of “My first multimeter” that one might have found in the 1980s. They weren’t too bad, I thought, and ordered one for less than a pint of beer in a British pub.

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Repurposing Moving Coil Meters to Monitor Server Performance

Snazzy analog meters can lend a retro flair to almost any project, but these days they often seem to be retasked as indicators for completely different purposes than originally intended. That’s true for these Vu meters repurposed as gauges for a Raspberry Pi server, and we think the build log is as informative as the finished product is good-looking.

As [MrWunderbar] admits, the dancing needles of moving-coil meters lend hipster cred to a project, but getting his Vu meters to cooperate and display network utilization and disk I/O on his Raspberry Pi NAS server was no mean feat. His build log is full of nice details on how to measure the internal resistance of the meter and determine a proper series resistor. He also has a lengthy discussion of the relative merits of driving the meters using a PWM signal or using a DAC; in the end, [MrWunderbar] chose to go the DAC route, and the video below shows the desired rapid but smooth swings as disk and network usage change. He also goes into great depth on pulling usage parameters from psutil and parsing the results for display on the meters.

Looking for more analog meter goodness? We saw a similar CPU load meter a few months back, and there was this mash-up of Nixies and old meters for a solar energy CEO’s desk.

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