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Saturday, 20 April 2013

Gauss 2 ... return of the gauss!

As promised here is part two of my home made gauss meter magnetometer project ... the dreaded circuit diagram. All pretty simple really: the 9v DC is smoothed by the 0.33uF capacetor before being reduced to 5v by the power supply module. Then the 0.1uF cap adds further smoothing before the voltage reaches the hall effect sensor. The output from the whole lot is then measured by the multimeter ... any cheap digital one will do.
In the next part I will talk you through assembly and interpreting the results ... happy days!

Tuesday, 2 April 2013

Is there a gauss in the house? Pt 1

My old Mk1 gaussmeter!

Why, you might ask, might an ordinary guitarist need a gauss-meter (or magnetometer)?  Er … well you can probably see why it might be useful to me as a pickup maker, dealing with magnets all day … but why might you want to make one? Well aside from curiosity and stuff like that … if you mess about changing guitar pickups etc and more importantly, occasionally swapping humbucker or P90 magnets … a tool that not only lets you tell the polarity of a pickup, but also its flux strength is a pretty cool thing to have.  You can even 'age' magnets yourself once you can measure before and after strength, and ...the clincher ... is when you discover that a DIY meter need only four components, and requires only that you can solder reasonably well to make it! You will need a digital multimeter to read the info your gauss meter is sending out, but many of us have one of those anyway, and a cheapo e bay one for six or seven quid is fine.

Reality check? Okay, so a cheap compass will work for checking pickup polarity ... and a Schatten polarity tester - from StewMac in the US - will do an even clearer job. But with postage, the Schatten (which is only a little magnet in a tube with one pole marked nort and the other south) will cost more than building a gaussmeter ... and one of these is WAY cooler and should cost less than a tenner ... fifteen to twenty quid if you have to buy a cheap multi meter!
Firstly the major component is a ‘hall effect device’. This little gismo is used in many applications, and has the neat property that when you feed it a nice stable voltage of say, five volts … a nice stable 2.5 volts comes out the other end.  ‘BORING’ you may cry … well yes, until you put the hall sensor in a magnetic field … then if the pole is ‘south’ the voltage goes up proportionally with the strength of the magnet … and if north, it goes down … again in proportion to the strength of the field. 
In theory we only need to feed that 5 volts in and measure the DC voltage ‘out’ with a digital multi meter  to have a crude, functioning gauss meter. In practise it’s only slightly more complex than that: if you intend to power the hall sensor from a 9v battery then you’ll need a ‘voltage regulator’ to deliver that 5 volts. Many people leave it at those two components … but I was taught that it’s a good plan to ‘filter’ the DC from the battery to the power supply and also filter the power supplies’ output to the hall sensor … just to provide nice squeaky clean DC where it’s needed.  That simply means a capacitor before the power supply and one after … simples!
I mounted everything on a small ‘perf board’ I had knocking about … they are only a couple of quid on e bay.
So here’s the component list , and we’ll get to the circuit diagram and hooking it up in part 2.
1x LM7805 voltage regulator
1x 0.33uF ceramic capacitor
1x0.1uF  ceramic capacitor
And last but most important … an Allegro A1302 Hall effect sensor
E bay is good for all of these … a chunk of ‘perf board’  to hook it all up on would be cool … and if you are feeling like being posh … a pair of banana sockets to attach the meter and a box to put everything in (you could use an old pedal enclosure).