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 for all sound cards. Very long period waves from distant quakes will certainly not register much through any sound card, but on some cards, 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”.) Continue reading
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.
Cutting wooden pieces for seismometer base
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. Continue reading
After about a year and a half of messing around, I finally got this very cheap seismometer system working and displaying real-time data under both Windows and Linux (More on how to set up Linux later.) Educationally, it has great potential.
It consists of the sensor and an interface box. This interface is radically different from traditional digitizing methods. The earthquake signal, after being amplified, then modulates a fixed 5 KHz 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.
This very cheap and rather unusual way to digitize an earthquake signal was inspired by my experience in ham radio, when AM transmitters were common. When I found the same principle (amplitude modulation of a carrier wave, or more correctly here, pulse amplitude modulation) used in “cheapchop“, even including the basic software, I was able to get it working.
Here is a screen shot of a local quake I recorded today. 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. Continue reading
(* BFO: “Beat Frequency Oscillator” a technical term describing the most common operating method used by metal detectors.)
The previous post mentioned the metal detector our students made during the winter vacation.
Following are the technical details:
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 were needed to complete the project. Continue reading
Hot Ice (Sodium Acetate) Experiment Success
Hot Ice Tower
Sodium Acetate: a chemical compound made by combining acetic acid and sodium bicarbonate, or simply just plain old vinegar and baking soda. It is used as a flavouring ingredient in snack foods and in hand warmers. Chemical formula: CH3COONa.
This is our second attempt at experimenting with sodium acetate (also known as “hot ice”). The aim was to create a tower using a solution of sodium acetate and water. It was a success!
Here is an easy way to demonstrate how sound is reproduced electronically.
This is how this simple speaker works:
(Note that on most speakers the magnet is stationary and the coil is attached to a moving cone.)
I made this video to show how an elevator affects the magnetometer trace. This is something, for those using a magnetometer to detect earthquake precurors, to be aware of. Notice the characteristic of the trace. Not to be mistaken as an earthquake precursor.
(Editor’s note: Simon is using the magnetometer described in this post. He lives on the 7th floor and sees very little traffic noise on his daily recordings, but at certain times of day he had been plagued by some very regular signals, always about the same size. In this video he shows how he finally tracked down where they’re coming from.)
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, such as the crane 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.
One cannot ordinarily record earthquakes via a computer sound card as they don’t respond much to the slow vibrations experienced in earthquakes. (Update: not strictly true. See my latest on this: Simplest Seismometer – Experiments with direct recording through PC sound card) However, with some cheap electronic trickery and clever software, it can be done, and very adequately for the purposes of study. The seismometer above, made by a high school student, in its first night of testing recorded this local 3.8 quake – a magnitude 1 in Taipei:
(click on the pictures for larger versions)
and as a surprise bonus, some filtering of background noise revealed this distant quake as well. It was a 5.9 from 1000 km away in the Philippines.
(Graphics Interchange Format, “GIF” is a computer image format that has become popular on the internet.)
It’s not very difficult to get children interested in computers. (What an understatement.) And if one hopes that their interest can be channeled into something useful, this is a fun way to start. Animated GIFs are a great way to create interesting web pages, blogs email attachments etc., and the ability to create them will be a useful skill in any future internet-related career. It’s not hard to learn how to make them. I’m describing here how I have made them on the Linux operating system. I use it for two main reasons:
1) It is all freely available software, so one will not be tempted to use pirated software and set a bad example.
2) Children are rarely familiar with it so they will not be distracted by their favorite games, chat programs etc.
These were some of my students’ first attempts.
Jonathan's table tennis player
Sodium Acetate: a chemical compound made by combining acetic acid and sodium bicarbonate, or simply just plain old vinegar and baking soda. It is used as a flavouring ingredient in snack foods and in hand warmers. Chemical formula: CH3COONa.
This is a video of a first attempt at experimenting with sodium acetate. Experiment performed in Taipei, Taiwan.
It was a fun experiment to do. The result wasn’t exactly what we were going for. Better luck next time.
To see the successful experiment go here: Sodium Acetate (Hot Ice) Experiment Success
(Click on photos to see full size image.)
A magnetometer such as this can detect small changes in the Earth’s magnetic field. It can be useful to monitor these changes as they may indicate the occurrence of natural phenomena that can influence our lives. Certain kinds of solar activity for example, have the potential to disrupt communications and power systems. Large earthquakes are also known to produce magnetic changes prior to their arrival. (This project was originally intended to work in conjunction with the search coil magnetometer project for predicting earthquakes.) Continue reading
Find out more about the book that started it all...
