Having fun playing with new Hall effect chips

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leftyretro

New Member
Well I like to pass on fun devices when I run across them, so I thought I would pass on two Hall effect items I just got off E-bay. I had heard and read about Hall effect devices before but never really had a need to actually try them, so it was a first for me to play with.

These are both very small devices but with long enough leads to be easy to use. They are pretty cheap and seem very stable and predictable, and don't take much 5vdc current to operate.

The first one, the A3213EUA is a switch.

http://www.newark.com/allegro-microsystems/a3213eua-t/hall-effect-ic/dp/65K5162

It has a open drain output that you pull up with a 10K or more resistor. It is high when there is no magnetic field and switches low when either a north or south magnetic field is sensed. In my bread board it could sense a flat, thin refrigerator magnet about an inch away from it's front face. Nice clean transitions with enough hysteresis to not cause bounce problems. Would be good for alarm switch, RPM sensor of rotating shafts and maybe home made switches using magnets for the buttons and I'm sure a zillion other fun applications.

The second, the A1323LUA-T is a analog output hall effect magnetic sensor.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=620-1028-ND

It has a 0-5vdc analog output that is normally at 2.5vdc with no magnetic field present. If it senses a south magnetic field it increase it's output voltage towards 5vdc. If it senses a north magnetic field it decreases it's output voltage towards ground. It's sensitivity rating is 2.5mv per Gauss, so I think that works out to be a +/- 1,000 guass range. This could be used as a position feedback sensor or some other exotic applications. It too seems stable and it's accuracy spec is worst case +/- 1.5%.

The linked items both have links to data sheets for these devices.

Lefty
 
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westaust55

Moderator
Having fun playing with Hall effect chips

HI Retrolefty,

I have been "playing with the Allegro UGN3503U hall effect sensor. :)

Much the same in a TO92 case.

Operates on 5Vdc with an analogue output of 2.5V at 0 gauss and can handle +/- 900 Gauss before going into saturation
 
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MFB

Senior Member
In the good old days when the Scientific American magazine had an amateur section, there was an article about measuring a cricket’s heart beat, by gluing a rear Earth magnet to its chest and picking up the very small movement with a linear Hall effect sensor. One interesting observation was that when distracted, by movement or noise, the heartbeat stopped. The cricket was not smart enough to think and make its heart beat at the same time.

All that is needed to display this kind of information is an instrumentation amp, PICAXE analog channel and a serial link to a PC that’s running the StampPlot software package.
 
hippy

hippy

Technical Support
Staff member
The cricket was not smart enough to think and make its heart beat at the same time.

Or maybe more smart than those observing :)

I seem to recall a lot of laughter when it was revealed the USSR had their fighter planes stuffed with valves instead of hi-tech IC's. Than someone mentioned EMP and it didn't seem such a silly idea after all.
 
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MartinM57

Moderator
As we digress, I used to work somewhere where we had an EMP generator...
...we used to (securely) tie down a Jaguar (the jet aircraft type), a pilot would sit in, 100% thrust on both engines...
...and fire EMPs at it to see what happened.

Happy days....
 
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MartinM57

Moderator
Well, that would be telling ;)

It was all highly classified at the time, and could still be to some extent I suppose.

But suffice to say, when an EMP hits an aircraft it induces all sorts of spikes into the wiring that can either be interpreted as valid signals causing various uncommanded engine and control surface movements. or causing equipment failure....the inside of an aircraft is a bit like the inside of a Faraday cage, but it unfortunately leaks radiation in through the cockpit and other big holes.

But as an EMP is of such a short duration the effects were over pretty quick - the more fun stuff was the EMC testing when we used to fire high powered radars at similarly tied down full throttled aircraft from ridiculously short ranges (imagine landing on a carrier for example). It was in the early days of high authority (and digital) engine and flight controls and continuous high powered radiation had interesting effects on engine operation and flight control surface movements :)

We needed proper pilots in the aircraft, all togged up and ready to go, just in case it broke free of the moorings...
 
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KIGX

Member
Retrolefty:

I am going to be building a wind speed indicator and was looking at Hall Effect switches but there were so many of them I couldn't figure out which one to try. It sounds like the first one you mention would work. Any comment?

Thanks
 
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boriz

Senior Member
Do you have any surplus 12v PC cooling fans to hand? They contain a hall effect device. Easily recovered/recycled. The one I pulled out had a two-transistor-Schmidt trigger-complimentary output so it could respond to the passing magnet and drive the coils directly. Great little device. You can probably get a handful of PC fans from a bargain bin for very little money.
 
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leftyretro

New Member
KIGX said:
Retrolefty:

I am going to be building a wind speed indicator and was looking at Hall Effect switches but there were so many of them I couldn't figure out which one to try. It sounds like the first one you mention would work. Any comment?

Thanks
Click to expand...
Yes, I think the hall switch would work great for that application.

Lefty
 
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BCJKiwi

Senior Member
Just a word (or two or more) of caution on the Hall effect devices as sensors.

If the Revs to be monitored are low, and the feedback required is fast (e.g. machine speed control) more than 1 pulse per rev is required and that means more magnets and I've found that 48 little magnets (24 on each of two shafts) add up to a tidy sum. Changed to reflective devices instead (simpler to implement in the application the gap type) - also available as switches or ratio-metric.

The ratio-metric types for gear tooth type sensing put out very low voltage changes which requires amplification so it's much easier to go with the switch type hence the need for many activators.
 
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rmeldo

Senior Member
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tony_g

Senior Member
o.t but after reading martins stories of past days it reminded me of something i heard before i left england i remember hearing about a police officer who was bored on radar duty for speeders so decided to try and measure an raf fighter jet passing by, apparently the planes systems went crazy thinking it was being targeted, cant imagine what sort of trouble the pc got into for that, never mind the pilot trying to fathom what was going on or if their was a general threat to the aircraft!!


tony
 
fernando_g

fernando_g

Senior Member
And let's not get started on dumb people pointing lasers at aircraft......

But back to hall cells and many magnets required ....sometimes a variable reluctance sensor will sense the teeth in a steel gear.
 
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Dave E

Senior Member
I agree that the Hall effect sensors are handy things and THIN.

I took on the task of finding a way to detect when one of 84 existing 12" cooling fans were going bad. The current way was to measure the air velocity by hand. That took an hour or so each time. I took a digital H.E. sensor, protected it's pins with some small heat shrink then hot glued it to a thin rare earth magnet, put heat shrink around the whole custom built sensor then glued it to the underside of the fan's finger guard just above where the 3 metal screws that hold the plastic fan blades on are located. There was only about a quarter of an inch of space between the guard and fan but there was room left over. Add a PICAXE, number crunch a few counted pulses and we now have 84 fan tachometers with an alarm to alert us when a fan's speed goes below a minimum speed. They have been working now for about 5 years with no failures except human caused ones.

Dave E.
 
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