Summary of The Magnetometer using PIC16F688
This article describes a DIY torsion magnetometer designed for San Jose, California, to detect small magnetic field variations. The device uses a suspended magnet with a mirror and a laser detector system. Key design challenges addressed include sensitivity versus stability, protection from air currents, damping oscillations caused by magnetic disturbances, and ensuring sensor stability against vibrations. The final construction utilizes PVC pipe and a PIC16F688 microcontroller for data recording.
Parts used in the Torsion Magnetometer:
- Magnet
- Mirror
- Thread (for suspension)
- Laser beam source
- Detector (sensor)
- PVC pipe (for construction)
- PIC16F688 microcontroller
- Chart plotting mechanism
I found several different magnetometer designs on Internet, but I tend to be very picky. None of those was what I needed – something that is sensitive enough to record the small magnetic field variations where I live (San Jose, California), robust enough to work for long periods of time without constant maintenance, and relatively easy to construct. Since the only place where I could permanently install the sensor away from disturbances is on the patio of our apartment, another important consideration was that it should not be influenced by major changes in temperature or humidity.
My magnetometer is of a torsion design. Torsion magnetometers work as follows: A magnet, attached to a mirror, is suspended from a thread. A laser beam is reflected from the mirror and falls on a detector. Changes in the Earth’s magnetic field turn the magnet and the attached mirror, twisting the torsion thread. The reflected beam changes its position on the sensor, the changes are recorded and plotted on a chart.
This sounds simple enough, but there are some precautions to be taken when designing such magnetometer.
First, the changes of the magnetic field, at least at the latitude of California, are quite small. Sensitivity of the magnetometer can be easily improved to detect those small changes by increasing the distance between the mirror and the detector. High sensitivity, however, comes at a price – any slight disturbance (say, by an air current) will cause tiny movements of the mirror that are enough to completely mess up the data. The mirror must be protected from such disturbances.
Magnetic disturbances abound too. A kid parking her bicycle nearby or a neighbor opening his refrigerator door is enough to set the mirror in motion. Once in motion, the mirror will keep oscillating for quite a while unless there is a way to dampen such oscillations.
Finally, the position of the sensor relatively to the mirror must be stable too. A rock-solid mirror won’t be of any use if the sensor moves this or that way with every slight vibration.
I came up with the following design, constructed out of PVC pipe:
For more detail: The Magnetometer using PIC16F688
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How does a torsion magnetometer work?
A magnet attached to a mirror is suspended from a thread; Earth's magnetic field turns the magnet, twisting the thread, while a reflected laser beam changes position on a detector. -
Can increasing distance between mirror and detector improve sensitivity?
Yes, increasing this distance improves sensitivity to detect small changes but makes the device more susceptible to disturbances like air currents. -
Why must the mirror be protected from disturbances?
High sensitivity means slight disturbances such as air currents can cause tiny movements of the mirror that mess up the data. -
What causes oscillation in the mirror?
Magnetic disturbances like a bicycle being parked nearby or a refrigerator door opening can set the mirror in motion, causing it to oscillate. -
How can oscillations be managed?
The design requires a way to dampen oscillations so the mirror does not keep moving for a long time after a disturbance. -
Is sensor stability important for the measurement?
Yes, the position of the sensor relative to the mirror must be stable because a rock-solid mirror is useless if the sensor moves with every vibration. -
What material was used to construct this specific magnetometer?
The described design was constructed out of PVC pipe. -
Which microcontroller is used in this project?
The project uses a PIC16F688 microcontroller for recording and processing the data.
