Retro Rear-Projection Numeric Display Gets A Teardown

We recently featured an entertaining project here, a digital clock with a variety of different retro display technologies forming its numerals. Among those was an extremely unusual device, a rear-projection display with an array of bulbs each able to shine through a different letter or numeral slide. There was such interest in this device that its owner [Suedbunker] subjected one to a teardown for all to see.

The displays came from an organ which he suggests may have been manufactured around 1900. We suspect that may be a rather early estimate due to its use of a printed circuit board, but it is no less a fascinating device for it. A rectangular enclosure secured by twist-tabs opens to reveal a matrix of small filament bulbs on a PCB and supported by a stack of resin boards, in front of which was placed a slide with a letter or number for each one. Before that lies a sheet of glass, and then a molded plastic lens assembly which provides an individual lens for each of the 12 bulbs. When a bulb is illuminated with these in place, the letter or number is projected on the screen at the front of the unit.

It has the advantage of simplicity, no need for a high voltage, and high-quality characters and flexibility in displaying alternatives through different slides, though at the expense of quite a bulky package. The bulbs are quite energy-sapping, so for his clock he replaced them with LEDs. We like it as one of the more practical retro numeric displays, but its size means we probably won’t see a comeback.

You can see our write-up of the clock using the projection display here.

A Gloriously Impractical Electromechanical Display

For this year’s office holiday party, [Gavan Fantom] wanted to do something really special. Coworkers were messing with LEDs to come up with displays and decorations, but they lack that old-school feel of mechanical displays. He wanted to create something that had retro look of moving elements, but didn’t want to just recreate the traditional flip mechanism we’ve all seen over and over.

The mechanism to drive a single “pixel”.

What [Gavan] came up with is breathtakingly impractical 8×8 display that sounds as cool as it looks. Each “pixel” in the display is a 3D printed screw mechanism rotated by a hobby servo. As the pixel is rotated in its case, it becomes progressively more visible to the observer. The opacity of the pixel can even be adjusted by varying the degree of rotation, allowing for rudimentary display of grayscale images.

Each element in the display is made up of seven 3D printed parts and two nails, which the mechanism slides on to move forward and backward. An 8×8 display needs 64 elements, which means the entire display needs 64 servos, 128 nails, and a whopping 448 3D-printed parts. Even with two printers attacking the production in parallel, the printing alone took over two weeks to complete.

The display is powered by a Raspberry Pi and three “Mini Maestro” controllers which can each handle 24 servos. [Gavan] found some sample code in Python to pass commands to the Maestro servo controllers, which he used as a template when writing his own software. The Python script opens image files, converts them to grayscale, and then maps the value of each pixel to rotation of the corresponding servo. He says the software is a little rough and that there’s still some calibration to be done, but we think the results are phenomenal so far.

Mechanical displays are a favorite of hackers, due in no small part to the awesome noises they make while in operation. While we’ve seen some very creative approaches to this type of display before, what [Gavan] has created here is certainly in a league of its own.

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Stromberg Carlson Charactron Tube

Flat panel TVs have spoiled us. It used to be that a big display took up a lot of room on your desk or living room because of the depth of the CRT’s electron gun. We wonder what the designers of the charactron would think if they could see our big flat screens today. Never heard of a charactron? Check out [uniservo’s] video of one of these old character display tubes.

You might think the device is just a simple small CRT. However, it is much stranger than that. Inside the tube was a stencil that contained all the characters the device could display. A deflection coil would move an electron beam to light up a particular character. Then another coil would deflect the patterned electron beam to the desired space on the screen. In some cases, the entire set of stencils would get the beam and the first deflection coil would pick which character made it through an aperture. Either way, the tube was not just a display, but a character generator.

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A Bluetooth Speaker For Babies

[Mike Clifford] of [Modustrial Maker] had not one, not two, but five friends call him to announce that their first children were on the way, and he was inspired to build them a Bluetooth speaker with a unique LED matrix display as a fitting gift. Meant to not only entertain guests, but to audio-visually stimulate each of their children to promote neurological development.

Picking up and planing down rough maple planks, [Clifford] built a mitered box to house the components before applying wood finish. The brain inside the box is an Arduino Mega — or a suitable clone — controlling a Dayton Bluetooth audio and 2x15W amp board. In addition to the 19.7V power supply, there’s a step down converter for the Mega, and a mic to make the LED matrix sound-reactive. The LED matrix is on a moveable baffle to adjust the distance between it and a semi-transparent acrylic light diffuser. This shifts the light between sharp points or a softer, blended look — perfect for the scrolling Matrix text and fireplace effects! Check it out!

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Making A Motorized Turntable Portable

[Robin Reiter] needed a better way to show off his work. He previously converted an electric TV stand into a full 360-degree display turntable, but it relied on an external power supply to get it spinning. It was time to give it an upgrade.

Putting his spacial organization skills to work, [Reiter] has crammed a mini OLED display, rotary encoder, a LiPo 18650 battery and charging circuit, a pair of buck converters, a power switch, and an Arduino pro mini into the small control console. To further maximize space, [Reiter] stripped out the pin headers and wired the components together directly. It attaches to the turntable in question with magnets, so it can be removed out of frame, or for displaying larger objects!

When first powered on, the turntable holds in pause mode giving [Reiter] time to adjust the speed and direction. He also took the time to add an optical rotary encoder disk to the turntable and give the gearing a much needed cleaning. Check out the project video after the break!

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Flip-Dot Display Brought Out of Retirement by New Drivers

LED matrix displays and flat-screen monitors have largely supplanted old-school electromechanical models for public signage. We think that’s a shame, but it’s also a boon for the tinkerer, as old displays can be had for a song these days in the online markets.

Such was the case for [John Whittington] and his flip-dot display salvaged from an old bus. He wanted to put the old sign back to work, but without a decent driver, he did what one does in these situations — he tore it down and reverse engineered the thing. Like most such displays, his Hannover Display 7 x 56-pixel flip-dot sign is electromechanically interesting; each pixel is a card straddling the poles of a small electromagnet. Pulse the magnet and the card flips over, changing the pixel from black to fluorescent green. [John] used an existing driver for the sign and a logic analyzer to determine the protocol used by the internal electronics to drive the pixels, and came up with a much-improved method of sending characters and graphics. With a Raspberry Pi and power supply now resident inside the case, a web-based GUI lets him display messages easily. The video below has lots of details, and the code is freely available.

You may recall [John] from a recent edge-lit Nixie-like display. Looks like he’s got a thing for eye-catching displays, and we’re fine with that.

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The Nixie Tube Killer That Never Was

With the wealth of Nixie projects out there, there are points at which Hackaday is at risk of becoming Nixieaday. Nixie clocks, Nixie calculators, Nixie weather stations, and Nixie power meters have all graced our pages. And with good reason – Nixie tubes have a great retro look, and the skills needed to build a driver are a cut above calculating the right value for a series resistor for an LED display.

But not everyone loved Nixies back in the day, and some manufacturers did their best to unseat the venerable cold cathode tubes. [Fran Blanche] came across one of these contenders, a tiny cathode ray tube called the Nimo, and after a long hiatus in storage, she decided to put the tube to the test. After detailing some of the history of the Nimo and its somewhat puzzling marketing — its manufacturer, IEE, was already making displays to compete with Nixies, and seven-segment LEDs were on the rise at the time — [Fran] goes into the dangerous details of driving the display. With multiple supply voltages required, including a whopping 1,700 V DC for the anode, the Nimo was anything but trivial to integrate into products, which probably goes a long way to explaining why it never really caught on.

If you happen to have one of these little bits of solid unobtanium, [Fran]’s video below will go a long way to bringing back its ghostly green glow. You might say that [Fran] has a thing for oddball technologies of the late 60s — after all, she’s recreating the Apollo DSKY electroluminescent display, and she recently helped a model Sputnik regain its voice.

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