So i bought an A3144 Hall sensor on a breakout board. Planning to use it to count revs for a speedometer. After fiddling around with it, have noticed:
it only reads when the magnet reaches 2 mm distance from the sensor - too close to be useful in my project
the output reads "1" and changes to "0" when the magnet approaches the sensor - seems to be the opposite of what it should do but maybe this doesn't matter?
The sensor has an open collector NPN output with a 10K resistor between Vout and VCC. With this configuration the sensor turns on (goes active) when it senses a magnetic field. When active the output is Low Logic Level. The data sheet:
OPERATION
The output of these devices (pin 3) switches low when the magnetic field
at the Hall sensor exceeds the operate point threshold (BOP). At this point, the
output voltage is VOUT(SAT). When the magnetic field is reduced to below the
release point threshold (BRP), the device output goes high. The difference in
the magnetic operate and release points is called the hysteresis (Bhys) of the
device. This built-in hysteresis allows clean switching of the output even in
the presence of external mechanical vibration and electrical noise.
While I haven't a clue of your magnetic force just using a simple household magnet should yield results at more distance than you are seeing.
the output reads "1" and changes to "0" when the magnet approaches the sensor - seems to be the opposite of what it should do but maybe this doesn't matter?
That is exactly how a pulled up output should act. It will read HIGH when no magnet is near and LOW when the magnet is close.
Would the sensor be more sensitive if I used a more powerful magnet?
Fridge magnets are pretty weak. A better magnet should work at a greater distance.
When I use those sensors I do not use an external pullup. I just enable the internal pullup on the connected pin.
That device has a rated operating flux density of between 70 and 350 gauss (0.007 to 0.035 tesla in
sensible units). Unless you make a good magnetic circuit with big magnets and place the sensor in a
narrow gap, you'll struggle to see high flux densities, you might get to 0.1T or so. Air is not a good
magnetic flux conductor (in physics language it has high reluctance).
By contrast the Earth's field is between 0.000025 and 0.000065 tesla - this Hall switch is not "sensitive"
by any stretch of the imagination, that's just marketing guff in the datasheet I'm afraid. Of that series
the A3141 has the highest guaranteed sensitivity. The A3144 has very poorly defined senstivity, the others
are basically bin-sorted by sensitivity, they are likely all the same device.
MarkT:
That device has a rated operating flux density of between 70 and 350 gauss (0.007 to 0.035 tesla in
sensible units). Unless you make a good magnetic circuit with big magnets and place the sensor in a
narrow gap, you'll struggle to see high flux densities, you might get to 0.1T or so. Air is not a good
magnetic flux conductor (in physics language it has high reluctance).
By contrast the Earth's field is between 0.000025 and 0.000065 tesla - this Hall switch is not "sensitive"
by any stretch of the imagination, that's just marketing guff in the datasheet I'm afraid. Of that series
the A3141 has the highest guaranteed sensitivity. The A3144 has very poorly defined senstivity, the others
are basically bin-sorted by sensitivity, they are likely all the same device.
That means 70 - 350 gauss should be enough to activate the switch? But you're saying should be able to get 1000 gauss with a magnet... so that should be enough to activate the switch? Sorry I don't know much physics