| This is the description of my magnetometer. What does a magnetometer do: It measures the direction of the magnetic North. This is influenced by the SUN, and with this equipment you cann predict Aurora's or Northern Light !
The principe of a magnetometer is very easy to understand: Just hang a small magnet on a thin thread and it will point to the North. By gluing a vane to the magnet, it acts like a very sensitive compass and the position of this vane can be measured with a light sensitive resistor.
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Some new pictures, only to show how small the electronics are. Just a few components are needed. Also look at the possibility to turn the magnetometer and the horizontal adjustment that can be done (picture 2). The last pictures shows how low the light level should be.
Remember: The joystick has 4 possible inputs. They are connected to pin 3,6,11 or 13 ! If not in use, connect a 47k resistor between output and + power supply, otherwise the reading of the values will slow down. So with using one magnetometer you need 3 times a 47 k resistor.
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My "long" version of a magnetometer. Made from some plastic tubing , 11 cm diameter. |
This is the innerside of a short version.
This is all the light that is needed, I'm sure the lightbulb will last "for ever". |
| Maybe some confusion can occur in the circuit below (see text above).
I've used a stir bar magnet, about 4 cm long. (as used in laboratorys) |
The electronics inside a magnetometer. Look at the vane, made out of a piece of black paper. Also look at the position of the light sensitive resistor (LDR) and the small light bulb. With the two variable resistors I have control of the light level, and with the otherone I can adjust the maximal resistanse of the LDR. Remember that the joystick works with 100 kohm, so before connecting to the PC, turn the 500 k into a position that you measure about 80 k between output and positive voltage connection. Do this measurement in the dark with only the light of the small lamp. This also means that you have to look for LDR's with a dark resistanse of more then 100kohm. |
The position of the vane and the LDR
joystick connecter
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Software, you can download . The program I made is called magneto6 , and was made with the old GWBASIC language I'm not quit shure if it is legal to download GWBASIC here, but hey, it is ancient . First make a sub directory and store both of them in this directory. Then start GWbasic.exe by double clicking. Type: Load "magneto6.bas" followed by ENTER The last thing to do is to start the program with the command: RUN ( followed by ENTER) It should work now , wait for "00"or "30" seconds to see the first data in the screen. ---------------- Statement: I felt the need to make a statement here, so I do it. I think , that in this modern time we're spoiled with a lot of big, fast computers. I started in a time, some 20 years ago with a 386 computer. In a time that a 40 mB harddisk was BIG , and 1 mB internal memory was huge ! A turbo button gave the possibility to switch to a higher speed ! That means from 8 to 16 mHz ! Now we laugh about these numbers, but remember that most of the time the computer is waiting to do the next step, only for playing good graphical games a lot of memory is needed and high speed. I'm pretty sure that this software will work on these ancient computers, so if you still have somewhere such a PC, clean it from the dust and start using it again !!!!!!!!!!!!!!!!!!!!
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Magnetometer graphs made on 7/8 jan 2005 . They display the changes in the direction of magnetic north of the earth. At about 23.30 houres (local time) a big disturbance is registrated. The total change of the magnetic north is nearly 1 degree !!! |
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| Screen shot of the original GWbasic program. See below for more details about my program and the graph you see in this screen. The green line in the graph is a control measurement of a resistor. This is to show that the changes are not from a malfunction of the computer. This green line is very stable ,between 21 and 24. |
EXCEL graph of the data The changes at 17.30 and 10.00 o'clock are due to arival and departer of me and my car. These changes are very quick, within 30 sec. From 12.00 to 14.00 o'clock the orange line showes the influence of my laundry dryer, that is standing in the neighbourhood of the equipment. |
Detailed EXCEL graph. As I saw these changes, my first and only reaction was "WOW !!!!" |
After a lot of experiments, and programming :these graphs shows what to expect. Remember it's made with very simple electronics. What you need is : two light sensitive resistors, a small light bulb , a magnet. Even the power is coming out of the computer ! Yes that's all for the electronics. An older computer will do the rest. The magnetometer is connected to the joystick input. The joystick input gives you 4 digital to analog converters. In fact it's a 8 bit converter, so in theory you have 255 steps in measurement level. Together with some software, written in GW basic, the data is measured and stored. It took me some time, but it does the things I wanted.
Some features: - each day at 11.59.30 o'clock , data is saved on floppy and on the hard disk (for safety a double saving), then at 12.00.00 the first measurent is done for the newly started periode of 24 houres. - two graphs are visible on the screen, one for the last 4 houres;one for the last 24 houres. - every 30 seconds new data is plotted in the 4 houres graph - every 3 minutes new data is plotted in the 24 houres graph - the amplifying can be changed with two inputs. Don't leave them unused. This will slow down the calculations in GWbasic. - when you have to work on the program, you have the possibilty to make a store of the allready gathered data. - each stored file gives info of the starting time, day , maximum and minimum value. Size off the stored file with 2880 data points in 24 houres = 17 kBytes. The files can be easily opened in EXCEL.
Just have a look at the screen dump placed on the right side of this page. In this picture you see two data lines, the green line is a control measurement ( a resistor is connected to the joystick). In this way you can see how good the stability is (max= 31; min=28). The yellow line is de magnetometer data. Click on the pictures for a bigger one ! |
This is how the actual screen looks like in GWbasic . |
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At about 7.15 I went to work. See the influence of my car, leaving the garage.
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