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?

.

<p>great project. many thanks for sharing.</p>
<p>this really useful. An actual piece of test equipment that does not have a uproc in it. Still an arduino could provide scale conversion and data logging among other features.</p><p>Great instructable! Thank you.</p>
Hi, <br>Can you please give any link to buy<br> that voltmeter cuz I'm not getting it at my location<br>Thanks
<p>hi</p><p>what is the minimum respone frequency of this sensor ?</p>
<p>The response time is 0.003ms is 334 Khz max.</p>
Thanks for response but I need minimum of response time of this sensor.<br>
<p>Hi</p><p>Great instructable!</p><p>I have a question.</p><p>The datasheet for the hall sensor ss495A states the sensitivity as</p><p>3.125 mV &plusmn; 0.125 mV/G.</p><p>How come we are using 1.3 as a factor?</p><p>Cheers</p>
<p>Sorry, the sensitivity factor is 3.125mV/G. I will change that, thanks!</p>
<p>Very nice, best I've seen. And I love the probe separation from box. Did I miss a schematic ... I'm electronically challenged and having to learn fast!</p><p>I am trying to measure much smaller magnetic fluxes put out by Helmhotlz coils down to the pT range. Can you help me with converting this to something usable that low? Would one of the other sensors work better for my application?</p><p>Again very nice and thanks for any help you can give me.</p><p>Doc31</p>
<p>The schematic you find in step 2, called the circuit. The data of this sensor you find below. Measuring in the pT range you need hall sensors like the TMR9001. I think that is an other category sensor (instrument), compared to the goal of this project.</p>
<p>Thank you. </p><p>After much looking, I have been unable to locate somewhere to buy the TMR9001 or even a price. I'm not sure they've even been released. Has anyone seen this for sale or in use? (Where? please)</p><p>I've also searched high and low for a circuit where this TMR9001 is utilized ... but nothing so far ... any thoughts where i might look or ideas as to how to modify this or another circuit?</p><p>I really appreciate the help</p>
<p>IamWe my past is close to your bio. I forgot to tell you that I love the last line of your bio!!!!!!!!!!!!!!!!!!</p>
I did find the schematic on the URL ... thank you.<br>And thank you for the suggestion of the TMR9001 ... I did some reading on it today.<br>And I agree that the original goal of this project was not what I am needing ... however ... is it possible to modify this circuit to accommodate the TMR9001? <br><br>Can anyone clue me in how to change this circuit or show me what is necessary to build another to accomodate this Hall effect sensor? <br>Again thank you IamWe
<p>Hmm, am I missing something? The datasheet suggests that when the SS495A reads 2.5V, the gauss is 0 and when at 4.5V, the max is about 640 gauss. http://www.farnell.com/datasheets/1683360.pdf </p>
<p>You are right.</p>
<p>Cool, I'm almost done with my gauss meter. It will measure <b style="">&plusmn;</b>3000 gauss!</p>
<p>That is the max linear range with this kind of Hall sensor. OK. for the most used small and middle size neodymium magnets. </p>
<p>I have actually found some that measure <b style="">&plusmn;4000 </b>gauss. The SS495A from Honeywell only measures <b style="">&plusmn;670 </b>gauss. </p>
is the lm339 substitutable for another part?
example two of the 8 pin comparators that make up the 339. also may i use a different hall efect somsor or have you calibrated your math from a gauss meter to the output of this sensor?
<p>Hello Zork, Yes, you can use also the dual comperator LM319 or LM393. Every ratiometric linear sensor has a milivolt to Gauss ratio. This you take with in the conversion math. So, you can use other brand's of Hall sensors. Some are working on a higher input voltage or have an other sensitivity. The 5V Hall sensor is handy because you can power it by a small 9V battery. The added paper gives a description of the SS495A sensor. Good for comparing data.</p>