Inside Electronic Gain Control

December 15, 2023 by Al Williams 18 Comments

Normally, if you want to control the gain of an amplifier, you’ll use a variable resistor. You know, like a volume control. But what if you want to control the amplifier’s gain with a voltage? [Engineering Prof] explains a circuit that can do this using a pair of op amps and a pair of matched JFETs.

The analysis is simple because you assume the op amps are not in saturation, so you can assume that the op amp will do what it needs to do to make the input terminals equal. The left-hand op amp has one input grounded, so the output will drive the first FET to ensure the negative terminal is also 0V. It is easy to see that the current through R1 must then be the current through the FET, which is going to be the control voltage (which is negative) divided by R1.

Continue reading “Inside Electronic Gain Control” →

DIY Tachistoscope Feeds Your Hunger For Popcorn And Propaganda

December 13, 2023 by Dan Maloney 12 Comments

You’ve probably heard of subliminal advertising — the idea is that behaviors can be elicited by flashing extremely brief messages on a movie or TV screen. “BUY POPCORN NOW” is the canonical example, with movies containing such subconscious messaging supposedly experiencing dramatic increases in popcorn sales.

Did it work? Maybe, maybe not, but the idea is intriguing enough to at least explore using this subliminal tachistoscope. [Roni Bandini] seems to have taken this project on as a sort of cautionary tale about brainwashing techniques, not only in motion pictures and TV but in printed media too; he goes pretty hard on the Peronistas’ use of not-so-subliminal messages to mold young Argentinian minds back in the 1940s and 50s.

The tachistoscope [Roni] presents is a little more sophisticated than those ham-fisted propaganda attempts. The Raspberry Pi-powered device downloads a video from YouTube and automatically replaces random frames with a propaganda message inspired by those used by the Peronistas, with the modified video piped to a composite video output for display on a TV.

A digital counter on the tachistoscope keeps track of the total time viewers have been propagandized. For extra fun, the machine has a switch to enable ChatGPT-created political messages to be inserted into the stream; we shudder to think what those might look like. Watch the video below for a sample of the brainwashing, but don’t blame us if you fall in love with [Evita].

We understand that this is more of a statement on the power of propaganda than an actual tool for mind control, but if [Roni] is serious about his brainwashing, some small mods might make it more effective. Thanks to the full frame of text on a black background, the subliminal messages aren’t very subliminal; they might be more subtle if the text was overlaid on the target frame rather than replaced completely. Seems like that should be possible with ffmpeg or something similar.

Continue reading “DIY Tachistoscope Feeds Your Hunger For Popcorn And Propaganda” →

A Fully-Transparent Air Bubble Display

December 6, 2023 by Kristina Panos 5 Comments

We all have good intentions when starting a new project, but then again, we all know where those lead. Such is the case with [RealCorebb]’s BBAir project, a completely transparent air bubble display. Although the plan was to spend about three months on it, the months slowly added up to a full year of tinkering.

It all started when [RealCorebb] made a subscriber counter using Minecraft campfire smoke to display the digits. Someone suggested using air to implement the next iteration, and for [RealCorebb], it was challenge accepted. After considering a syringe for each channel, a separate pump, or one pump and many solenoids, [RealCorebb] settled on solenoids to push air, and designed a PCB to reduce the amount of wire spaghetti.

Once [RealCorebb] created an acrylic enclosure and wired everything up, it was time to test it out. Everything worked, except that air was leaking from somewhere, which turned out to be the way the solenoids were installed. Then, of course, it was time to don sunglasses and write the code. We still don’t know if [RealCorebb] settled on water, glycerine, or silicone oil, but the end result is quite nice, and we’re betting on glycerine. Be sure to check out the build video after the break, which has English subtitles.

Although we’ve seen our share of bubble displays before, we often discuss bubble LEDs displays like this one.

Continue reading “A Fully-Transparent Air Bubble Display” →

A Single Board Computer, With Vacuum Tubes

December 5, 2023 by Jenny List 8 Comments

We have occasionally featured vacuum tube computers here at Hackaday and we’ve brought you many single board computers, but until now it’s probable we haven’t brought you a machine that combined both of these things. Now thanks to [Usagi Electric] we can see just such a board, in the form of his UE-0.1, a roughly 260 by 210 mm PCB with 24 6AU6 pentodes on board that implements a simple one-bit CPU.

The architecture starts with the MC14500B 1-bit microcontroller, which was the subject of a previous vacuum tube computer. People found the unusual architecture difficult to understand, so this board is an even simpler take. It doesn’t have all the features of the Motorola original but it is (just) enough to be a CPU.

The tubes are arranged in groups of four with heaters in series from a 24 V supply, while the inputs and clock come in the form of on-board suitably retro-looking switches. The final touch is a VFD of the type used in bar graphs, were used to show the state of the various bits. It’s a fully working computer in the simplest sense, and definitely worth a look in the video below the break.

It would be interesting to see whether the tube count could be reduced further, or is this a record. The number of physical devices could be cut by using tubes with more than one device in them such as double-triodes, but perhaps that would be cheating.

Meanwhile, if you think vacuum computing is all about the old stuff, perhaps you should look at the state of the art.

Continue reading “A Single Board Computer, With Vacuum Tubes” →

Honey, I Ate The Camera

December 2, 2023 by Jenny List 17 Comments

We like cameras here at Hackaday. We like them a lot. But until now that liking has never extended to liking their taste. A build from [Dmitri Tcherbadji] could change all that though, and he’s created a working Fuji Instax Square camera made from gingerbread.

To look at, it’s a straightforward box camera, albeit one made from sheets of gingerbread stuck together with what looks like icing. The film rests in an off-the-shelf development unit but the rest is edible, including unexpectedly the lens which is made of sugar glass. The photos it returns are definitely somewhat cloudy, but that it works at all is a significant feat.

While it’s an unconventional choice it’s clear that gingerbread, or at least a baked material similar to it, could become a useful tool in a maker’s arsenal. In this case it’s light-proof, but were instantly curious about how well a moulded piece of dough might hold its shape when baked. He reports the gingerbread expanding in the oven, however we’re guessing that tuning the quantity of raising agent could help.

Home-made cameras have featured here many times, but Instax seems to pop up most often as a hacked in replacement for obsolete Polaroid packs.

The Minimum Required For A Film Camera

November 30, 2023 by Jenny List 13 Comments

Film cameras can be complex and exquisitely-crafted masterpieces of analogue technology. But at their very simplest they need be little more than a light-proof box with a piece of film at the back of it, and some kind of lens or pinhole with a shutter. [ChickenCrimpy] adds the most basic of 35 mm cartridge to create what he calls the Minimum Viable Camera. It’s a half-frame 35 mm pinhole film camera with the simplest possible construction.

It can be built from almost any flat light-proof 3 mm thick stock, though something that you can run through a laser cutter is probably ideal. Once snapped together to make to box-like structure, tape is added along the joins for light-proofing. The film is reeled from a full 35 mm cartridge to an empty one, and cranked back frame-by-frame by means of a wooden key that engages with the spindle.

There’s no lens, instead this is a pinhole camera, and the shutter is a piece of the stock held on the front of the camera with bolts and butterfly nuts. Taking a photo is as simple as pointing the device at the subject and lifting the shutter away for a few seconds. There’s a video overview for the project which we’ve placed below the break.

It’s true that this camera needs a moment in the darkroom to load, but we like its extreme simplicity and the ethereal and grainy pictures it produces. If you fancy an introduction to 35 mm photography you could definitely do worse.

Continue reading “The Minimum Required For A Film Camera” →

A Tube Guitar Amp For A Modest Budget

November 27, 2023 by Jenny List 17 Comments

There’s a mystique among both audiophiles and musicians about vacuum technology, thus having a tube amp still carries a bit of a cachet. New ones can be bought for eye-watering prices and old ones can be had for the same price with the added frisson of unreliability. Happily it’s surprisingly straightforward to build your own, as [_electroidiot] shows us with a fairly inexpensive build.

The design is inspired by the guitar amps of the 1950s and 1960s so it’s not for audiophiles. The circuit is a pretty conventional single-ended one with a two stage double triode preamp and a single power output tube. The transformers are usually the difficult part of a build like this one, and here instead of resorting to using a mains transformer for audio they come from a defunct 1960s Phillips radio. We especially like the old-school construction technique with a folded aluminium chassis and liberal use of tag strips on which to build the circuits.

The result is something that would have been in no way out of place in the 1960s, and proves that tube circuitry isn’t beyond the constructor in 2023. If it’s whetted your appetite for more, we can help you there.