A cute acute triangle.

Posts from: March '15


Today I'll describe a tiny project that I did dome time ago, which finds a connection between TVs, infrared and some mints.

Introduction (sort of)

I'm thinking that school programmes, especially with regard to natural sciences, could be taught in a more intresting manner. The theory is often fine by itself, but the teachers miss to address some questions which are invariably going to occur to the kids (maybe not to all kids; just the more curious ones) and puzzle them later. xkcd has a very good example with the physics lesson where we learn about the "bird-inspired" airfoil shape, and how it manages to generate lift. Yet nothing is done to address the obvious question: airshows regularly feature fighter aircraft flying upside-down — but the plane doesn't fall down despite the wrong orientation. What's more, the explanation (regarding the angle of attack) can be trivially tested by any sixth-grader waving his hand outside the side window of a moving car!

It's probably expected that these questions are addressed after classes, but in our schools that generally doesn't happen, or, at least, very few ask the teacher questions outside the curriculum. And it's better if everyone is trained to ask questions and locate potential problems in the theory. The airfoil is not an isolated exaple - many times, the theory given is at least shallow, or there are obvious defects sticking out of it.

A similar experience of mine was the explanation of infrared rays. They told us that all things emit IR, amount depending on temperature. We were also told (but probably in a different class) that TV remotes also work with IR. What they didn't explain is how the TV-set differentiates between the former and the latter types of IR. Yes, in a calm room, the "background" IR are more or less static and I imagined, that the TV can differentiate that easily. But what will happen, if you put your TV opposite to a well-kindled fireplace? I've seen this thing happen and I imagined that the TV will change channels or enters menus or otherwise go awry. Nope.

It was after I got into electronics that I found out this powerful pattern of digital circuits. It's easy to generate a signal, a short one (from human point-of-view), yet sophisticated and specific enough that the nature has no chance to emit it ever, even in millions of years. What's more, these signals, at least for IR remotes, are well described and categorized, in tabular form. From there, some smart guy had taken upon the idea of creating an universal device, which can turn off any TV. You press a button, and, in the span of one minute, the codes for "On/Off" in all possible IR encoding schemes for every known TV are sent (there are more than 60 variants, as each manufacturer apparently created his own). The device is discreet enough to be hidden in a purse or a pocket, so you can surreptitiously turn off that annoying TV in the bar, because you've come here for an intellectual discussion while eating, and watching football (for example) just doesn't qualify...


So at some point I ordered the TV-B-Gone kit from Adafruit (there are ready-made units, but I wanted a custom one). Assembled, it comprises of a small circuit board with 4 protruding LEDs (with slightly different spectrum and sreading characteristics), a button, and a holder for 2xAA cells. However, this way it can't be easily carried arround. The protruding part would easily break off, and the gentle conductors to the holder wouldn't last long. So I thought about an enclosure - either polymer clay, or a ready-made from Farnell... Finally, a coworker saved me from wondering further by giving me one tin box from Altoids mints, which he apparently brought from the US. His exact words were - "I see that you do some electronics, this will help".

I had previously seen a lot of american hobby electronics sites and I wondered somewhat about their obsessive fixation on these boxes. As if there was nothing else with that purpose on the market! You made an emergency phone charger out of a nine-volt battery and 7805? Put it in an Altoids box. Headphone preamp? Altoids. Guitar Effect? Altoids.

It was after I fooled some with it that I realized how good it was. It has a lid. And it's held shut tight, the hinges are not some feeble plastic. You want to show what's inside? No problem:

TV-B-Gone exposed

And here's how it looks when shut closed:


What's more, the 2xAA holder fits exactly to the width of the box. The circuit board then fits just tight to the remaining length. Coincidence? I don't think so:


You might be wondering why the microcontroller (in this case, an 8-bit Atmel) doesn't command the LEDs directly, why there's a transistor per each. The reason is that the LEDs are powerful (that's why it's powered by AA, not AAA cells) - the idea being that the device can turn off a TV 50 meters away. It packs quite a punch, unlike a regular TV remote. Even more, if you look straight at the LEDs, in a dark room, you can even see how they blink. Who said humans cannot see IR?

Drilling holes for the LEDs and the switch is trivial, and in the end you have a wicked device, inconspicuously hidden in a box of breath mints:


I could hardly thought of a more treacherous device — victory for science (with a hint of cinnamon)!

Posted in category Hardware -- clock 15 Mar 2015, 10:42, 2 comments




Posted in category Images -- clock 3 Mar 2015, 22:22, 0 comments



So, I survived this:


I was a bit surprised how useful the superstitions among the general public are. The flight was pleasant and the cabin looked kinda ... empty :)

Posted in category Images -- clock 1 Mar 2015, 22:39, 0 comments




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