Nov 04 2009
During my daily morning mainline injection of news on the Net this week, a couple of electronics projects caught my eye that I hadn't seen before. The first is a project from SparkFun Electronics that uses higher voltage than I'm used to working with - a Geiger counter kit with a USB interface. The kit is constructed around the popular ATmega 168 microcontroller, which means that the basic Arduino development kit can be used to write code that pulls samples from the Geiger-Muller tube (powered by a tiny high voltage power supply) and outputs numerical values over USB, where the 'counter shows up as your average, every day serial device. The nifty thing about this project is (other than the fact that you've just built a Geiger counter that is) is that the suggested tutorial project is the construction of a random number generator that is seeded with background radiation. Truly random numbers are pretty hard to come by in the field of cryptography, where they are primarily used in the generation of keying material. They're easy to generate poorly (i.e., not really random) and surprisingly difficult to do well. Case in point.
I've considered playing around with something like this for a while but stayed away from it largely because the high voltage power supplies give me the willies. I've been lit up accidentally a few times and, on the whole I never want to repeat the experience. I've also considered building an RNG like this one to set up my own EGG project but never quite got around to doing so. At any rate, this seems like fun and if any of the other things I mentioned appeal to you, you might want to consider investing an afternoon in building and playing with one - maybe you could test the output of it and see how well it generates random numbers.
The other thing that jumped out at me seems like a something-for-nothing deal unless you understand the principle behind it - a radio transmitter powered by the user's voice. The circuit is powered with an electrical current generated by speaking into the loudspeaker (wired up as a microphone) rather than a battery; remember, an electrical generator and an electric motor really aren't all that different in construction. Michael Rainey, who constructed El Silbo, clocked the RF output power of the prototype between 5 and 15 milliwatts and reports successful communication at a range of 100 miles. A later revision of the circuit uses a different microphone element and a solid-state amplifier, resulting in a peak output of 100 milliwatts. Most impressive!