If you’re a long-time Hackaday reader like we are, you’ll certainly remember a rash of projects from around ten years ago that all (mis-)used an LED as a light sensor. The idea wasn’t new, but somehow it made the rounds and insinuated itself into our collective minds. Around the same time, a cryptographic cipher with an exceptionally small memory footprint was also showing up in hacker projects: TEA (Tiny Encryption Algorithm).
This old project by [Marcin Bojanczyk], [Chris Danis], and [Brian Rogan] combines both the LED-as-light-sensor meme and TEA to make a door-entry keyfob that works over visible light. And they do so using almost nothing — a few LEDs and just over 2Kb of code. It’s pretty sweet.
Which brings us to the question: where are they (LED-sensors and TEA) now?
LED-as-light-sensor was just cool. We certainly loved the idea back in 2006. But [Forrest Mims] had been using the phenomenon for decades back then. It certainly makes sense when you’re trying to squeeze as much as possible out of as little as possible, or when budget is a main concern and you just can’t afford an extra photodiode.
But our own experience with LEDs as light sensors is that the results are extremely variable across different LEDs. Code that works with water-clear red LEDs might not work with the ones that come in red-tinted plastic, for instance. Is that why they went extinct?
Similarly, the TEA family of ciphers showed up in a bunch of projects around this time, from the badge for the HOPE conference in 2010 to a widely used RFM12B radio library. There are a couple of attacks on XXTEA, but they only affect reduced-round versions of the cipher, and rely on a tremendous amount of intercepted data — more than we’d see in a home-automation network over years.
Over the last five years or so, there’s been a lot more Internet of Things, which means using standard Internet-style encryption methods (AES and so on) that are widespread on non-memory-constrained computers. Is that what happened to XXTEA?
Anyway, we got tipped off to a project that combined a few of our favorite (old) ideas in one, so we thought that we’d share. Thanks [Blue Smoke] for the walk down memory lane. Any of you out there keeping the flame(s) alive? Have you used sensing LEDs or XXTEA? Are those projects still going, or do you have any future projects planned with these tricks still up your sleeve? Let us know in the comments below.
Before the modern notion of the citizen scientist lies the earlier ideal of the independent scientist. Scientists outside of the academic community but engaging with it. These days citizen scientists are often seen as valuable assistants in the scientific process, helping collect and process data in a quantity which would be otherwise intractable.
In the past however, independent scientists had a far more central role. Galileo, Kepler, Darwin and Hooke were all self funded at various points in their careers. More recently independent scientist Peter Mitchell won the Nobel prize for Chemistry in 1978 for his foundational research into cell biochemistry and the development of the chemiosmotic hypothesis.
Sadly, peer-reviewed scientific contributions by scientists un-sponsored by a research organization are now few and far between. In this short series we hope to highlight the efforts of these lone researchers with particular reference to the tools they’ve had to hack together on a budget in their scientific quests (if you know an independent researcher you think we should feature, please comment below!).
In Hacker circles Forrest Mims is perhaps best known for his series of electronics books and the unforgeable Atari Punk Console. But it’s his ability to engage with the scientific community as an independent researcher through a series of well thought out scientific articles that interests us here. Contributions made all the more significant by his lack of formal scientific training.
Continue reading “Citizen Scientist: Forrest Mims”
Sometimes, the best birthday presents are the ones you give yourself. In [Dino]’s case, they’re the ones you make for yourself. In honor of his 55th, he built the Sqonkbox 55, a 13-note cigar box organ based on a 555 and amplified with an LM386.
It’s based on a 555 wired in astable mode, turning it into an oscillator that outputs a frequency. This frequency is determined by the resistors between pins 6 and 7, another between 7 and 8, and the capacitor between pin 2 and ground. [Dino] shows a breadboard version first, with a single tuning pot and momentary acting as a piano key. As he explains, this portion of the circuit is repeated 13 times with pots and momentaries that he arranges like piano keys through the lid of a cigar box.
“Sqonkbox,” you ask? A second 555 in astable mode sends the output through an LED. This LED stands face to face with an LDR, and they are shrouded in this configuration with black heat shrink tubing. The ‘sqonk’ 555 changes the frequency of the first 555, providing a clippy, rhythmic tone at the rate set by a potentiometer. [Dino]’s full video of the build is after the break. A BOM is forthcoming, but it’s easy enough to puzzle it out between the video and the lovely, Forrest Mims-esque schematic. Continue reading “Sqonkbox 55 is a Cigar Box Organ of Awesome”
If you’ve ever dealt with a brightly lit Christmas tree, you might understand the frustration of having to crawl underneath the tree to turn the lights on and off. [brmarcum] feel’s your pain. He’s developed his own motion activated AC switching circuit to turn the lights on and off automatically. A motion sensor ensures that the lights are only on when there are people around to actually see the lights. The circuit also has an adjustable timer so [brmarcum] can change the length of time that the lights stay on.
The project is split into several different pieces. This makes the building and debugging of the circuit easier. The mains power is first run through a transformer to lower the voltage by a factor of 10. What remains is then filtered and regulated to 9VDC. [brmarcum] is using a Parallax PIR sensor which requires 4.5V. Therefore, the 9V signal is then lowered once more using a voltage divider circuit.
When the PIR sensor is triggered, it activates the timer circuit. The timer circuit is driven by a 555 timer. The circuit itself was originally borrowed from a classic Forrest Mims book, though it was slightly modified to accommodate the PIR sensor. The original push-button trigger was removed and replaced with the signal from the PIR sensor. The only problem is that the circuit was expecting a low signal as the trigger and the PIR sensor outputs a high signal. [brmarcum] resolved this problem with an NPN BJT to invert the signal. Once the timer is triggered, it flips on a relay that allows the mains electricity to flow through to the lights.
[brmarcum] soldered the entire circuit onto a piece of protoboard. The final product was then mounted securely inside of an insulated plastic case. This allows him to mount the circuit safely underneath the Christmas tree skirt. The PIR sensor is kept external to the enclosure and wired up into the tree itself. This allows the sensor to still detect motion in the room while the rest of the circuit is hidden away.