vfd

78 Articles

Jet Engine Tachometer Turned Into Unique CPU Utilization Meter

May 4, 2023 by 16 Comments

When you’ve got a piece of interesting old aviation hardware on your desk, what do you do with it? If you’re not willing to relegate it to paperweight status, your only real choice is to tear it down to see what makes it tick. And if you’re lucky, you’ll be able to put it to work based on what you learned.

That’s what happened when [Glen Akins] came across a tachometer for a jet airplane, which he promptly turned into a unique CPU utilization gauge for his computer. Much of the write-up is concerned with probing the instrument’s innards to learn its secrets, although it was clear from the outset that his tachometer, from Kollsman Instruments, was electrically driven. [Glen]’s investigation revealed a 3-phase synchronous motor inside the tach. The motor drives a permanent magnet, which spins inside a copper cup attached to the needle on the tach’s face. Eddy currents induced in the cup by the spinning magnet create a torque that turns the needle against the force of a hairspring. Pretty simple — but how to put the instrument to work?

[Glen]’s solution was to build what amounts to a variable frequency drive (VFD). His power supply is based on techniques he used to explore aircraft synchros, which we covered a while back. The drive uses a trio of MCP4802 8-bit DACs to generate three phase-shifted sine waves via direct digital synthesis with an RP2040. The 3-phase signal drives the motor and spins the dial, with 84-Hz corresponding to full-scale deflection.

The video below shows the resulting CPU utilization gauge — which just queries for the current load level and sends it to the RP2040 over serial — in action. It’s not exactly responsive to rapid changes, but that’s to be expected from a mechanical system. And compared to exploring such a nice instrument, it really doesn’t matter.

Continue reading “Jet Engine Tachometer Turned Into Unique CPU Utilization Meter” →

More Drill Press Mods: Adding A VFD Means No More Belt Changes

March 10, 2023 by 29 Comments

A decent drill press is an essential machine tool for almost any kind of shop, and marks a significant step up in precision compared to a hand drill. The ability to drill square, true holes is one thing, but the added power over what’s possible with a portable tool is the real game changer. If only you didn’t have to switch around those damn belts to change speeds, though.

You don’t, of course, if you go through the effort to add a variable frequency drive to your drill press like [Midwest Cyberpunk] did, along with some other cool mods. The donor tool for these mods came from — where else? — Harbor Freight. Some will quibble with that choice, but the tool was pretty cheap, and really all [Midwest] was interested in here was some decent castings and a quill with acceptable runout, since the entire power train of the tool was slated for replacement. The original motor gave way to a beefy Baldor 3-phase/240-volt motor controlled by a VFD mounted on a bracket to the left of the drill press head, allowing the stock belt and step pulley transmission to be greatly simplified. Continue reading “More Drill Press Mods: Adding A VFD Means No More Belt Changes” →

This Retro Game Console Puts Vacuum Fluorescent Display To Good Use

March 7, 2023 by 4 Comments

Small in size, low-resolution, blocky segments, and a limited color palette — all characteristics of the typical vacuum fluorescent display, any of which would seem to disqualify them as the display of choice for a lot of applications. But this is Hackaday, and we don’t really pay much attention to what we’re supposed to do, but rather to what’s fun and cool to do. So when we see something like a VFD game console, we just have to sit up and take notice.

In a lot of ways, the design of [Simon Boak]’s Arduino-based VFD console is driven by his choice of display. The Noritake Itron GU20X8-301 VFD is a “tricolor” display with eight rows of 20 rectangular pixels. Each pixel is composed of six short linear segments, with alternating red and blue colors. Turning on either set of segments yields one of the two base colors, while turning on both yields a sorta-kinda whitish color, if you squint a bit.

[Simon] chose a two-piece design for his console, with a separate controller and display. The controller holds the Arduino Nano and all the controls, plus a piezo buzzer for fun. The display case connects to the controller with a ribbon cable and holds the VFD power supply and driver. To celebrate the retro look of the VFD, both cases are decked out with woodgrain side panels. [Simon] chose appropriately blocky games for the console, like Snake, Conway’s Game of Life, and the venerable snow demo. We’d imagine Pong would be a good choice too, as well as perhaps Tetris if the display were flipped on its side.

We really like the look of this console, and we appreciate putting an otherwise obsolete display to use in a creative way. If you want to learn a little more about these displays, check out this love letter to the VFD.

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A Loving Look Inside Vacuum Fluorescent Displays

February 26, 2023 by 20 Comments

Everyone knows we’re big fans of displays that differ from the plain old flat-panel LCDs that seem to adorn most devices these days. It’s a bit boring when the front panel of your widget is the same thing you stare at hour after hour while using your phone. Give us the chunky, blocky goodness of a vacuum fluorescent display (VFD) any day of the week for visual interest and retro appeal.

From the video below, it seems like [Posy] certainly is in the VFD fandom too, rolling out as he does example after example of unique and complicated displays, mostly from audio equipment that had its heyday in the 1990s. In some ways, the video is just a love letter to the VFD, and that’s just fine with us. But the teardowns do provide some insights into how VFDs work, as well as suggest ways to tweak the overall look of a VFD.

For example, consider the classy white VFDs that graced a lot of home audio gear back in the day. It turns out, the phosphors used in those displays weren’t white, but closer to the blue-green color that VFDs are often associated with. But put a pink filter between the display and the world, and suddenly those turquoise phosphors look white. [Posy] does a lot of fiddling with the stock filters to change the look of his VFDs, some to good effect, others less so.

As for the internals of VFDs, [Posy]’s look at a damaged display reveals a lot about how they work. With a loose scrap of conductor shorting one of the cathodes inside the tube, the damaged VFD isn’t much to look at, and is beyond reasonable repair, but it’s kind of cool to examine the spring mechanisms that take up slack as the cathodes heat up and expand.

Thanks to [Posy] for this heartfelt look into the VFDs of yesterday. If you need more about how VFDs work, we’ve covered that before, too.

Continue reading “A Loving Look Inside Vacuum Fluorescent Displays” →

Audio Amp Puts VFDs To Work In An Unusual Way

December 8, 2022 by 14 Comments

It’s safe to say that most projects that feature a VFD emphasize the “D” aspect more than anything. Vacuum fluorescent displays are solid performers, after all, with their cool blue-green glow that’s just the right look for lots of retro and not-so-retro builds. But that doesn’t mean there aren’t applications that leverage the “V” aspect, such as this nifty audio preamp using VFDs as active components.

The inspiration behind [JGJMatt]’s build came from the Korg Nutube line of VFD-based low-voltage dual-triode vacuum tubes. Finding these particular components a little on the expensive side, [JGJMatt] turned to the old standby DM160 VFD indicator tube, which is basically just a triode, to see how it would fare as an amp. The circuit takes advantage of the low current and voltage requirements of the VFDs — the whole thing runs from a USB boost converter — by wedging them between a 2N3904 input stage and a 2N2007 MOSFET output. There’s a mix of SMD and through-hole components on the custom-etched PCB, with a separate riser card to show off the VFDs a little bit through the front panel of the 3D printed case.

All in all, we find this little amp pretty cool, and we love the way it puts a twist on the venerable VFD. We’ve seen similar VFD amps before, but this one’s fit and finish really pays off.

Garmin HUD Got Discontinued, But Not Trashed

October 30, 2022 by 10 Comments

The Garmin HUD+ was a small Bluetooth device intended for the dashboard of a car, meant to be used as a GPS heads-up display for data from Garmin smartphone apps. It used a bright VFD (vacuum fluorescent display) which was viewed through a clear reflector, and displayed GPS information and directions. It was discontinued in 2015, but [Doz] was fond of his and used it happily until a phone upgrade meant it no longer worked. Was it destined for a landfill? Not if he had anything to say about it!

The first thing [Doz] tried was using an alternate Android app, but since it also didn’t work, it was time to sit back and reflect on the scope of the issue. In [Doz]’s case, he really only wanted some basic meaningful data displayed, and decided he could do away with the phone altogether if he had the right hardware. Continue reading “Garmin HUD Got Discontinued, But Not Trashed” →

VFD Character Display Turned Into Audio VU Meter

March 9, 2022 by 8 Comments

Humans love visualising music, whether it’s in the form of an inscrutable equation drawing squiggles in Winamp, or a simple VU meter pulsing with the beat. This build from [mircemk] is of the latter variety, repurposing a VFD display to do the job.

The project is built around a VFM202MDA vacuum fluorescent display, which provides that lovely green-blue glow we all know and love, driven by a PT6314 driver chip. This has the benefit that it can be readily driven by a microcontroller in much the same way as the familiar HD44780 character LCD driver chip. With some minor tweaks, the character set can be modified to allow the display to become a surprisingly-responsive VU meter.

An Arduino Nano runs the show, with an envelope follower circuit feeding a signal for the left and right channels into the analog inputs of the microcontroller. The Arduino then measures the voltage on those inputs and feeds the necessary commands to the PT6314 driver to update the display.

The resulting VU meter has 38 bars per channel, and is highly responsive. The fast flickering of the meter bars in response to the music make it compelling to watch, and the era-appropriate enclosure the project is built in adds plenty to the aesthetic.

We’ve seen other VU meter builds before too, like this one that uses a little physics knowledge to create a more realistic analog-like needle meter. Video after the break.
Continue reading “VFD Character Display Turned Into Audio VU Meter” →