A3144 Hall Effect sensors

Thread Starter

spinnaker

Joined Oct 29, 2009
7,837
I have a few of these A3114 Hall Effect sensors sitting around. that I would like to use in a project.

https://www.elecrow.com/download/A3141-2-3-4-Datasheet.pdf

First to power it. All I will have is 12V and 3V. Minimum for this device is 4.5V so I will have to use the 12V supply.

I need 3V out. I think I am reading the datasheet correct but just want a confirmation. I can supply with 12V but add a pull up resistor to my 3V supply. Is this correct?

Now for the hard question. I need a small magnet for space and weight reasons . I was going to go with one of these.


https://www.hobbytown.com/1-16x1-32-rare-earth-disc-magnets-200-by-national-imports-magcraft-nsn0591/p546362

which would be ideal but I am afraid the small size would make lining things up a challenge so I am considering one of these.

https://www.hobbytown.com/1-8x1-16-rare-earth-disc-magnets-100-by-national-imports-magcraft-nsn0566/p546352

Would wither of these magnets be enough to trip the sensor?
 

ebeowulf17

Joined Aug 12, 2014
2,953
I have a few of these A3114 Hall Effect sensors sitting around. that I would like to use in a project.

https://www.elecrow.com/download/A3141-2-3-4-Datasheet.pdf

First to power it. All I will have is 12V and 3V. Minimum for this device is 4.5V so I will have to use the 12V supply.

I need 3V out. I think I am reading the datasheet correct but just want a confirmation. I can supply with 12V but add a pull up resistor to my 3V supply. Is this correct?

Now for the hard question. I need a small magnet for space and weight reasons . I was going to go with one of these.


https://www.hobbytown.com/1-16x1-32-rare-earth-disc-magnets-200-by-national-imports-magcraft-nsn0591/p546362

which would be ideal but I am afraid the small size would make lining things up a challenge so I am considering one of these.

https://www.hobbytown.com/1-8x1-16-rare-earth-disc-magnets-100-by-national-imports-magcraft-nsn0566/p546352

Would wither of these magnets be enough to trip the sensor?
I've tried numerous times to find useful data and methods for predicting magnetic field strength (in Gauss, as detected by such sensors,) based on magnet properties, but it's never straightforward. The field strength decays with distance in a very strange way (transitioning from an inverse cube law relationship to an inverse square law relationship at one point if I remember right.) The angles of the magnet and the sensor play a role, and the presence or absence of other nearby materials with high magnetic permeability also changes things. It's overwhelming...

That said, depending on how close they get, I'm pretty confident those magnets can trip those sensors. I regularly work with small-ish 1/4" x 1/4" x 1" magnets that generate >700 Gauss fields with a little space between magnet and sensor (can't remember specifics, but I think I max out my sensor with the magnet still at least 1/4" away from the sensor.) Your worst case trip point is much lower at only 175 Gauss, so it won't take much to generate that weaker field.

How close will the magnets be to the sensors when you want them to trip?

Also, I think you've got it right as far as pull-up resistors and output voltage.
 

ebeowulf17

Joined Aug 12, 2014
2,953
Oops! I misread the part number. You've got the one with higher trip points. I still think you've got a decent chance, depending on how close the magnets will get. But, as I said before, it's pretty difficult to model and predict this stuff - ultimately you'll just have to test some magnets and see how they do.
 

Dodgydave

Joined Jun 22, 2012
8,571
The A3144e will work from 4.5V to 24V, it has an Open Collector output so put two pullup resistors in series say 10k and 2k7 across the 12v supply ( 10k to 12v 2k7 to ground) and put the output to the junction of the resistors, then when the magnet is present the output will go to 2.55V, when the magnet is removed the output will go to zero.


I use minature magnet 3x2mm and it detects at a distance of 12mm.


https://cpc.farnell.com/comus-assemtech/m1219-2/button-magnet-3x2mm/dp/SN35930?st=Magnet
 
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Thread Starter

spinnaker

Joined Oct 29, 2009
7,837
The A3144e will work from 4.5V to 24V, it has an Open Collector output so put two pullup resistors in series say 10k and 2k7 across the 12v supply ( 10k to 12v 2k7 to ground) and put the output to the junction of the resistors, then when the magnet is present the output will go to 2.55V, when the magnet is removed the output will go to zero.


I use minature magnet 3x2mm and it detects at a distance of 12mm.


https://cpc.farnell.com/comus-assemtech/m1219-2/button-magnet-3x2mm/dp/SN35930?st=Magnet

But I also have a 3V supply. Why can't I just tie my collector to the 3V? Why do through the hassle of a voltage divider?
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,837
Ok do that then, put a 10k to the 3v rail..

OK thanks for confirming both of my questions. I am off to the hobby store as soon as they open. ;)

Oh another question. I have read that these devices are not the best for high RPM tachometer sensors. Any truth to that?
 

ebeowulf17

Joined Aug 12, 2014
2,953
I don't care about magnetic strength. All I care about is its presence.
Of course, but the ability to detect its presence is a function of distance, sensitivity of the sensor, and magnet strength. For any given sensor, you can detect a stronger magnet at a greater distance. Or, for any given distance, you need higher sensitivity to detect a weaker magnet.

That's why I was speculating about field strength, and also why the question of distance is important.

I can't imagine why these would be bad at high RPMs. Based on the rise time specs, they should work fine switching at >100kHz. Orders of magnitude better than needed from what I can see.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,837
I used one for a points replacement on a cdi ignition motorbike , works a treat no misfires even at 8000 rpm.

Working like a champ. I was a bit concerned of the disk being imbalanced. I had to use a larger magnet as it is the smallest they had at the hobby shop but it works great. The disk is plexiglass.


Nice sharp square wave too.

upload_2018-10-28_19-43-10.png

I still need to tie it to a 12V supply with pull up to 3V rail. Right now I just have it tied to 5V.

Thanks for the advice.
 
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