Author: Jenny List

3295 Articles

Flame Triodes Don’t Need Any Vacuum

May 26, 2016 by 37 Comments

There is a rich history surrounding the improvisation of electronic components. From cats-whisker foxhole radio detectors using razor blades through radio amateurs trying antique quartz lenses as crystal resonators and 1950s experimenters making their own point-contact transistors, whenever desirable components have been unavailable the ingenuity of hackers and makers has always sought to provide.

In an age when any component you might wish for is only a web browser and a courier package away, you might think there would be no need for such experiments. But it is in our curious nature to push the boundaries of what can be made without a factory at our disposal, so there are still plenty of ingenious home-made components under construction.

One such experiment came our way recently. It’s a few years old, but it’s a good one. [Nyle Steiner, K7NS] made a working triode without any form of vacuum, instead its medium is a flame. He’s demonstrated it as a rectifier, amplifier, and oscillator, and while it might not be the best triode ever it’s certainly one of the simplest.

In a traditional vacuum triode the current flows as electrons released from a hot cathode and are able to cross the space because there are no gas molecules for them to collide with. The flame triode has an abundance of gas, but the gasses within it and its immediate surroundings are also strongly ionized, and thus electrically conductive. Flame ionization detectors have exploited this phenomenon in scientific instruments for a very long time.

A roaring flame might not be the most practical thing to keep in your electronic equipment, but [Nyle]’s experiment is nonetheless an impressive one. He’s posted a video showing it in action, which you can see below the break.

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Arduino Motion Detection With A Bit Of Wire

May 23, 2016 by 55 Comments

It is likely that many of us will at some time have experimented with motion detectors. Our Arduinos, Raspberry Pis, Beaglebones or whatever will have been hooked up to ultrasonic or PIR boards which will have been queried for their view of what is in front of them.

[Connornishijima] has stumbled on a different way to detect motion with an Arduino, he’s polling an ADC pin with a simple length of twisted pair hooked up to it and earth, and reliably generating readings indicating when he (or his cat) is in its vicinity. He’s calling the effect “Capacitive turbulence”, and he’s open to suggestions as to its mechanism. He can only make it work on the Arduino, other boards with ADCs don’t cut it.

Frequent Hackaday featuree [Mitxela] may have also discovered something similar, and we’ve hesitated to write about it because we didn’t understand it, but now it’s becoming unavoidable.

It’s always dangerous in these situations to confidently state your opinion as “It must be…” without experimental investigation of your own. Those of us who initially scoffed at the idea of the Raspberry Pi 2 being light sensitive and later had to eat their words have particular cause to remember this. But this is an interesting effect that bears understanding. We would guess that the Arduino’s fairly high input impedance might make it sensitive to mains hum, if you did the same thing to an audio amplifier with a phono input you might well hear significant hum in the speaker as your hand approached the wire. It would be interesting to try the experiment at an off-grid cabin in the woods, in the absence of mains hum.

If you’d like to give his experiment a try, he’s posted his sketch on Pastebin. And he’s put up the video below the break demonstrating the effect in action, complete with cats.

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A Minitel Terminal As A USB Linux Terminal

May 22, 2016 by 20 Comments

If you paid a visit to France in the 1980s the chances are you’d have been surprised to see a little brown screen and keyboard sitting next to the telephones wherever you went. At the time, it was another reason apart from the food, wine, and super-fast trains to envy our Gallic cousins. This was Minitel, their take on the cutting-edge of online data services of the day.

Minitel stood apart from similar services of the day in most other countries, because of its business model. Unlike the UK’s Prestel or West Germany’s BTX for which you had to spend significant money on a terminal, the French Minitel terminals were free. Thus in the early 1980s everybody in France was busy using videotext while most of the rest of Europe was still excited by chipping bits of flint into arrow heads. Or at least, that’s how it seemed at the time to those of us who didn’t have Minitel.

The Minitel service was finally shuttered in 2012, but the terminals can still be found. [Tony Pigram] bought one, an Alcatel Minitel 1, and made it into something useful by turning it into a USB serial terminal for his Raspberry Pi. Surprisingly the physical interface between the Minitel and the USB port is a relatively simple level shifter, but the configuration of both the Minitel and the Pi was anything but.

The problem was that Minitel terminals were meant to work with Minitel, and [Tony]’s difficulties were increased by his machine being an earlier model without the handy function key to access settings found on later terminals. A lot of research paid dividends though, and he now has what must be one of the most compact and stylish CRT serial terminals available. We can’t help noticing it has a QWERTY keyboard and English menus, it would be interesting to know which non-French market it was made for.

We’ve featured an RS-232 integration into a Minitel terminal before here at Hackaday, but if you are really interested in Gallic retro-tech take a look at our discussion of their 8-bit scene.

PTC Heaters For Reflow Soldering

May 21, 2016 by 12 Comments

Reflow soldering – setting components on a PCB in blobs of solder paste and heating the whole assembly at once to melt all joints simultaneously – has been the subject of many ingenious hacks. Once it was the sole preserve of industrial users with specialist microprocessor-controlled ovens, now there are a myriad Arduino-controlled toaster ovens, hot air blowers, and hotplates that allow hackers and makers to get in on the reflow act too.

This morning a fresh idea in the reflow soldering arena has come our way. It’s not the most earth-shattering, but it does have some advantages so is worth a second look. [Analog Two] has successfully used a PTC heating element as a reflow soldering hotplate.

PTC heating elements are thermistors with a positive temperature coefficient. As their temperature rises, so does their electrical resistance. By careful selection of materials they can be manufactured with a sharp increase in resistance at a particular temperature. Thus when an electrical current is passed through them they heat up until they reach that temperature, then the current decreases as the resistance goes up, and they do not heat beyond that point. Thus as heaters they are intrinsically self-regulating. From our point of view they have another advantage, they are also cheap. Fitted as they are to thousands of domestic heating products they are readily available, indeed [Analog Two] found his on Amazon.

The heater chosen was a 200W 110V model with a temperature of 230 Celcius to match the solder he was using. They are also available for other mains voltages, and even at 12 and 24V for automotive applications. He reports that the time to reflow was about 90 seconds.

We’ve mentioned the advantages of this heater as its price and regulated temperature. Looking at the pictures though a disadvantage is its size. This is a reflow plate for small boards. There are larger PTC heater elements available though, it would be interesting to hear people’s experiences reflowing with them.

Hotplates for reflow soldering have featured before a few times here at Hackaday. We recently had this tiny plate, but we’ve also had a PID-controlled plate, and an Arduino-controlled domestic hotplate. We’re sure this is an avenue with further to go.

Using An FPGA To Generate Ambient Color From Video

May 20, 2016 by 4 Comments

We should all be familiar with TV ambient lighting systems such as Philips’ Ambilight, a ring of LED lights around the periphery of a TV that extend the colors at the edge of the screen to the surrounding lighting. [Shiva Rajagopal] was inspired by his tutor to look at the mechanics of generating a more accurate color representation from video frames, and produced a project using an FPGA to perform the task in real-time. It’s not an Ambilight clone, instead it is intended to produce as accurate a color representation as possible to give the impression of a TV being on for security purposes in an otherwise empty house.

The concern was that simply averaging the pixel color values would deliver a color, but would not necessarily deliver the same color that a human eye would perceive. He goes into detail about the difference between RGB and HSL color spaces, and arrives at an equation that gives an importance rating to each pixel taking into account its saturation and thus how much the human eye perceives it. As a result, he can derive his final overall color by looking at these important pixels rather than the too-dark or too-saturated pixels whose color the user’s eye will not register.

The whole project was produced on an Altera DE2-115 FPGA development and education board, and makes use of its NTSC and VGA decoding example code. All his code is available for your perusal in his appendices, and he’s produced a demo video shown here below the break.

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Hackaday’s Fun With International Mains Plugs And Sockets

May 19, 2016 by 205 Comments

When we recently covered the topic of high voltage safety with respect to mains powered equipment, we attracted a huge number of your comments but left out a key piece of the puzzle. We take our mains plugs and sockets for granted as part of the everyday background of our lives, but have we ever considered them in detail? Their various features, and their astonishing and sometimes baffling diversity across the world.

When you announce that you are going to talk in detail about global mains connectors, it is difficult not to have an air of Sheldon Cooper’s Fun With Flags about you. But jokes and the lack of a co-starring Mayim Bialik aside, there is a tale to be told about their history and diversity, and there are also lessons to be taken on board about their safety. Continue reading “Hackaday’s Fun With International Mains Plugs And Sockets” →

I2c Relay Expander Uses Nifty Card-Edge Connection

May 18, 2016 by 24 Comments

[Andrew Sowa] wanted to use an off-the-shelf relay board from Numato Labs. The board lacks a suitable computer interface, which meant that [Andrew] would have to build one, and its input connectors are screw terminals, which meant a lot of wiring. Undeterred, he created an i2c expansion board using an MCP23017 I/O port expander, and with a novel card-edge designed to mate with the screw terminals, solving both problems at once.
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