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Hall effect sensor

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Electronman

New Member
Hi,

A have took a PC fan Apart and found a 3 pins hall effect sensor inside it.
I used it to lighten a 12V bulb via a neodymium magnet in 4cm distance.
Now I want to know if there is any electrical way to increase the distance to more than 8cm?

Thanks.

P.s, How those 4 Pins hall effect sensors do work? and why they have 4 pins?
 

Sceadwian

Banned
It's not particularly practical to increase their distance, you can't modify the sensor, best you can do is use a much more powerful magnet or a pulsed electromagnet, why would you want to though?
 

dougy83

Well-Known Member
you could possibly use a flux guide of some sort either on the magnet or the sensor. Just a vague thought...
 

Sceadwian

Banned
The distance from the test device isn't vacant then though, might as well just put the hall effect sensor on a stick.
 
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Electronman

New Member
you could possibly use a flux guide of some sort either on the magnet or the sensor. Just a vague thought...

What is a Flux Guide?

I just want to control a bulb by that.

It seem these sensors are able to directly measure the Magnetic filed, Right?
My sensor just become an conductor when I put the magnet near it. so It is an ON/OF component not a liner sensor, so how it does so?
 

Electronman

New Member
Another question which I faced several minutes ago is:
I am able to convert the hall sensor to an RPM meter and then put the output to a calculator, "to traces of "+" button via 2 wires". I will send a voltage to the calculator while I just want to Short the pins of the + button, then Do you know anyway to do it without any relay? I mean Can KILL the voltage across the incoming wires of the output of the hall sensor somehow so that I cause it to be shorted at some time?
 

AllVol

New Member
Another question which I faced several minutes ago is:
I am able to convert the hall sensor to an RPM meter and then put the output to a calculator, "to traces of "+" button via 2 wires". I will send a voltage to the calculator while I just want to Short the pins of the + button, then Do you know anyway to do it without any relay? I mean Can KILL the voltage across the incoming wires of the output of the hall sensor somehow so that I cause it to be shorted at some time?

Use the hall effect sensor to drive a transistor which will short the calculator wires.
 

colin55

Well-Known Member
Inside the hall effect item are three things. The actuall Hall effect circuitry (item), a high gain amplifier and a Schmitt Trigger.
The actual Hall effect device (item, circuitry) is a linear item but the amplifier and Schmitt Trigger turns the detection into an on/off output so that the coils in the fan will be energised.
You cannot get to the actual Hall effect circuitry.
 
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Sceadwian

Banned
Why are you trying to use a hall effect sensor as an RPM counter at that distance? IR would make a lot more sense. Hall effect sensors are generally used at extremely close distances. What dougy means by a flux guide is a rod of ferrite material that would concentrate the magnetic field. I'm going to guess you're not going to get 8cm's out of it though. You would need to get a linear hall effect sensors and some decent amplifier electronics, even then you'd still need a strong magnet.
 
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MrAl

Well-Known Member
Most Helpful Member
Hi,

A have took a PC fan Apart and found a 3 pins hall effect sensor inside it.
I used it to lighten a 12V bulb via a neodymium magnet in 4cm distance.
Now I want to know if there is any electrical way to increase the distance to more than 8cm?

Thanks.

P.s, How those 4 Pins hall effect sensors do work? and why they have 4 pins?


First method would be to place a hunk of ferrous metal in front of the sensor.
That increases it's sensitivity. The increase depends on the metal so you
might try several kinds of metals or simply several different kinds of metal
objects.
One such object that works a little is a metal binder clip. It's not that great
though, but acts as a metal 'core'.
Another object would be a piece of transformer metal like the kind you find in
wall warts (made for 60Hz). You need to get the grain orientation correct
though in relation to the HE device.

Second method is to 'bias' the Hall Effect Sensor with another small magnet
placed close to the HE sensor but not close enough to trigger it. If you get
the pole right, when you bring another magnet with the same pole somewhere
in the vicinity it will trigger the HE device at a distance that would end up
being closer to the HE chip. This is probably the best method because it allows
a lot of change of sensitivity.
The small magnet may be placed off to one side slightly, but some experimentation
could yield the best results. You'll need to get it just right so that it will also
allow the device to turn off too. How well it works will depend partly on the
magnetic hysteresis of the actual part you have.
You can also use this method to desensitize the HE device a little by placing the
smaller magnet with it's opposite pole toward the HE device.
 
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dougy83

Well-Known Member
Second method is to 'bias' the Hall Effect Sensor with another small magnet placed close to the HE sensor but not close enough to trigger it.
Very clever!

EDIT: If there's a schmitt trigger in the sensor, you'd have to ensure the bias is less than the lower threshold... or the sensor will latch in the one state (but easily checked).
 
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Boncuk

New Member
You would need to get a linear hall effect sensors and some decent amplifier electronics, even then you'd still need a strong magnet.

He could use a Jackhammer. It has a real strong magnet. :)
 

Sceadwian

Banned
EDIT: If there's a schmitt trigger in the sensor, you'd have to ensure the bias is less than the lower threshold... or the sensor will latch in the one state (but easily checked).

That's a relatively complex way of saying if you get a magnet too close it'll get stuck on =\
 

MrAl

Well-Known Member
Most Helpful Member
Very clever!

EDIT: If there's a schmitt trigger in the sensor, you'd have to ensure the bias is less than the lower threshold... or the sensor will latch in the one state (but easily checked).

Hi there Dougy,

I have to say it is clever of you for noticing that too! I guess you are
on your toes :)

One nice way around the hysteresis problem is, if possible, to use TWO
magnets as the actuator and one as the bias. The one small low power
magnet would be for the bias of course, and one larger magnet for
the 'on' pulse (say N pole toward HE device) and the other larger magnet
mounted a small distance away from the first larger magnet but with
it's opposite pole (would be S pole here) toward the HE device. If
they were both mounted on a shaft for example the N pole would turn
the hall effect device on and the S pole would turn it off.
Yeah, it's a little harder to do with three magnets but that's life he he.
 
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