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#3057256 - 07/21/10 08:56 PM Re: 2 questions regarding USB current and Hall Sensor sensitivity. [Re: aRareKindOfMonster]  
Joined: Aug 2007
Posts: 293
Brandano Offline
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Brandano  Offline
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Posts: 293
Caput Mundi (well, it used to ...
I am using some Allegro A1302 and they seem to work fine. If anything they are too sensible to the magnets I got, rare earth magnets off a cheap Chinese knock off magnetic construction set. these toys are dangerous, since the magnets will easily come loose, but are a good source for relatively cheap, powerful magnets. In any case neodymium magnets are easy to find on ebay

Inline advert (2nd and 3rd post)

#3057393 - 07/22/10 12:28 AM Re: 2 questions regarding USB current and Hall Sensor sensitivity. [Re: Brandano]  
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aRareKindOfMonster Offline
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Thanks Brandano.

OK, one detail that was initially to be clarified, a sensor's sensitivity. I am sorry if I didn't phrase the question more intelligibly.

Brandano, you say your A1302 are "too sensitive to the magnets" you got. They are rated at 1.3mV/G.

Julian, in his PDF suggest the use of the the A1321 since they have a sensitivity of 5 mV/G.

Forgive me for being a pain, but shouldn't a lower mV/G value translate into a higher sensitivity or is it the other way around.

#3057532 - 07/22/10 05:50 AM Re: 2 questions regarding USB current and Hall Sensor sensitivity. [Re: aRareKindOfMonster]  
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julian265 Offline
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A lower mV/G number is less sensitive - it's the number of millivolts the sensor output changes by per gauss of flux density change.

My sensors have a 2 mm gap between them and the magnet - which gives minimum to full voltage over about 45 degrees of stick travel.

The sensitivity won't matter as much if:
you have very strong magnets, or
want more than 45 degrees of travel, or
you're willing to calibrate the stick to give full travel at reduced voltage - which hurts stick resolution.

In general higher sensitivity sensors are better, because you can usually increase the sensor to magnet gap to reduce it, but once the sensor hits the magnet you can't increase it.

#3057677 - 07/22/10 02:22 PM Re: 2 questions regarding USB current and Hall Sensor sensitivity. [Re: julian265]  
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Brandano Offline
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Brandano  Offline
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Julian is right, my sensors are less sensitive. However, the magnets I am using are fairly strong, they are set up so that they are only 6 mm apart and caged to further improve the magnetic flux from the free poles. I get a little less than 90 degrees of useful range (45 degrees each direction), at their extremes the sensor appears to be saturated. That at least seems the case from the joystick raw reading, which gives me perfect centering, but some 2 to 5 degrees of "dead zone" at the stick extremes. Unless this is a behavior of the autocalibration of my HOTAS cougar. I use it mostly on Linux, and the manual calibration utilities there don't seem to cope properly with the resolution of the cougar. To be certain I'd have to attach a multimeter to the sensor's output to see what the actual voltage swing it... I could do that, I guess, but I am happy enough with the fact that it just works smile

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