I don’t think I’ve ever made anything with such an impressive-sounding name before. Doesn’t it sound like something out of a sci-fi movie?
I didn’t make this as a project for my students – it’s a bit advanced. Rather I made it as part of my ongoing quest to record electromagnetic earthquake precursors: one of the ways in which they might be observed is by recording small changes in the Earth’s magnetic field. Thus my interest in magnetometers.
In this post I am not talking about the chopped audio method used in all my previous devices. This one is just straight audio – directly into the PC’s sound card.
Some time ago I had bought into the idea that “you can’t record earthquakes through a PC’s sound card because they don’t respond to low frequencies,” in fact I had repeated it myself. But recently I’ve found that this is not strictly true. Very long period waves from distant quakes will certainly not register much through a sound card, but quite good results can be obtained with local quakes and P waves from strong, distant quakes. (The trace in the above photo shows P waves from a 7.3 quake in Japan, a little left of center. Ignore the other stuff to the right of it; that’s “student quakes”.)
Several classes were run this summer. A few projects were repeated for the new, mostly younger students, while some of our older students made the pendulum seismometer described in this previous post.
This is quite an advanced project. While we did spend some time on theory, such as the differing speeds of P and S waves and how their arrival times allow us to calculate how far away an earthquake was, we didn’t go into much more as it starts to invlove math concepts that are way above their level. However, as they learn more in school, I’m sure they’ll get much more out of it than most, since they will have seen those theories in action in the real world.
The radios described here are a regenerative design utilizing a single JFET and cheap audio amplifier integrated circuit.
(JFET: “Junction Field Effect Transistor”, a small electronic device which can amplify radio signals and is used as the basis for these radios.
Regenerative: employing “regeneration” (feedback), a technique used in simple radio designs to increase the amplification of radio signals.)
Here in Taiwan, there don’t appear to be many people dabbling in radio as a hobby. My recent experiments with simple radios that students might be able to make, have been regarded somewhat like “black magic”. So it hasn’t been too difficult to get students interested in it and a few of them have made the radios described below with very good results.
After about a year and a half of messing around, I finally got this very cheap seismometer system working under Windows. It also displays data in real time – something I have still not accomplished with Linux. Educationally, it has great potential.
It consists of the sensor and an interface box which amplifies and converts the signal into an audio tone. That plugs into the microphone socket of a computer running three pieces of software under Windows (XP in the one shown here). They are, 1) the one I put together – “seismochop”, which retrieves the earthquake signal from the audio tone and converts it to serial data, 2) a virtual serial port package called com0com which acts as a relay, and 3) Amaseis – software that records and displays earthquake data. These three can be downloaded free.
Here is a screen shot of a local quake I recorded today. (USGS Event ID usc00096va) There’s a DOS window I brought to the foreground for the screen shot. That’s seismochop showing the data samples at about 11 samples per second.
(* BFO: “Beat Frequency Oscillator” a technical term describing the most common operating method used by metal detectors.)
Here are the technical details of the metal detector our students made during the winter vacation.
A great activity that will get kids out of the house during vacations (and away from computer games) is hunting for “treasure” with a metal detector. This winter, after some R&D work I finally worked out a design that would be easy enough for youngsters to make and use, but still powerful enough to find small things like coins.
(The technical details of it will be posted soon have been posted in a separate post here.)
Although the electronics work was not totally new to them (these students had made the morse key project earlier) it still required close supervision, so we only ran two small classes of three students each. About fifteen hours was needed to complete the project.
Here is an easy way to demonstrate how sound is reproduced electronically.
This is how a speaker works:
By Graeme Keon
The father’s sentence was abruptly cut off by the boy’s, “Well I don’t care! OK?!!!” shouted in a kind of sulky, “Look what you’ve done to me” tone of voice, then the “BAM!” of the slamming door. Another futile attempt at talking some sense into him was over. The father got a grip on his temper, mulled over some possible disciplinary actions, then finally walked away in a quandary. Coming down heavy on him had never helped in the past – it only seemed to worsen the situation. At least it was quiet – nothing but a few keyboard and mouse clicks from the other side of the door.
Wasn’t it obvious there would be consequences if his homework wasn’t done? And he hated doing poorly in tests yet didn’t seem to want to do anything about it.
Several classes were run this summer. Once again we found it very difficult to get the students to go home at the end of the two and a half hour course periods. It seems they just can’t get enough of this! Here is a summary of their activities:
Most of the projects required some woodwork so a lot of sawdust was flying around in the beginning.
The 4 wheel drive car continues to be a popular project and several were made this summer.
