Everyone likes magnets. Playing with the invisible magic force of permanent magnets is from all ages.

Tinkering with coils, relays and many other magnetic devices needs sometimes a measuring tool for magnet field density and North and South Pole detection.

With a Gauss meter you can measure a magnetic field. Gauss or Tesla is the unit for 'magnetic flux density' or 'magnetic induction'.

This project shows a simple, sensitive and reliable meter with a North- South Pole display. In a shop you pay around 120 dollar for a good Gauss meter. The few components for this project cost about 10 dollar.

I am really surpriced with the performance of this device. Anyone can build this instrument, a handy tool for your home makerspace. Watch the video to see how it works.

Step 1: The Video

Features:

- High sensitivity ~3 mV/G

- Digital display voltmeter

- North- South Pole indicator LED

- Aluminium sensor Probe detachable

- Simple design, easy to build

- Cheap, about 10 dollar components

Step 2: The Circuit

The circuit is build at a small piece of PCB.
Only four main components are there:

- voltage regulator (LM7805),

- Ratiometric Linear Hall Effect Sensor (SS495A from Honeywell),

- mini digital voltmeter

- window comperator (LM339).

The device is powered by a 9V battery. A voltage stabilizer makes 5V for the Hall sensor. The output of the Hall sensor is connected to the digital voltmeter and a window comperator. This last circuit is build around 2 of the 4 gates of the LM339, to switch the N or S pole LED on/off. There is only one setpoint for the LED senitivity between the North (red LED) and the South (green LED).

The only thing to do, is to make a table with the conversion numbers between voltage and the Gauss or Tesla units. The voltmeter shows normally 2.5V (the zero point). With a higher density of the North pole the volt meter goes from 2.5V to 0V and for the South pole from 2.5V to 5V.

Conversionrate is: 1V is 1300 Gauss and 1 gauss = 0.0001 Tesla or 1 Tesla = 10,000 Gauss. OK!

Step 3: Conclusion

Making a sensitive, reliable and cheap Gauss Meter is an easy job. When all components are connected in the right way, the meter is just working fine. Only one potmeter there to trim the N/S LED sensitivity.

Making a nice housing is up to you. I choose for a metal mint box. The voltmeter I put in a small plastic box on top. Also the N/S pole LED's are inside the displaybox. The sensor is on top of a small aluminium tube, this to take distance from the iron box. Avoid iron near the Hall sensor which can affect the measurement.

When I did a check around the screen of my Imac, I found 22 magnetic fields. Time for iron shielding?

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