Hall Effect Magnetometer-Amplifier?

[steveb]

Originally Posted by levangram

I have to put my voltage leads to + and - of Vin.So,what do i have to put in them so that my indication will be zero when it's actually 2.5V?
....The important thing is to make it work after a zero adjust so that it will display zero in a zero magnetic field..

OK, so if you put the negative on the output of a 2.500 VDC reference voltage IC and the positive on the output of the opamp, it should work. The 2.500 VDC reference voltage would be on the noninverting terminal of the OPAMP also.

The Hall effect sensor has an internal 2.500 voltage reference circuit in it. This is why it outputs 2.5 volts with no field. I'm suggesting that you use your own external 2.500 V reference IC chip as a reference point. Many different chips are available, but if you need help in selecting one, I'm sure someone here will recommend one.

[levangram]

I don't have a 2.500 VDC reference voltage IC,so i managed to zero my field with the use of a pot.I connect the output of the sensor and the wiper of the pot to my indicator,and adjusting the pot,i actually zero my field.
What i'm trying now is to use the op amp so that my new output will be 0.4 of the original(original comes from the output of the sensor and the wiper of the pot).I have a 741,but i dont know which wire goes where!!
a)which wire goes to op amp -?
b)which wire goes to op amp +?
c)does an op amp needs to be supllied to work?And if so,with what voltage?

[steveb]

Originally Posted by levangram

I don't have a 2.500 VDC reference voltage IC,so i managed to zero my field with the use of a pot.I connect the output of the sensor and the wiper of the pot to my indicator,and adjusting the pot,i actually zero my field.
What i'm trying now is to use the op amp so that my new output will be 0.4 of the original(original comes from the output of the sensor and the wiper of the pot).I have a 741,but i dont know which wire goes where!!
a)which wire goes to op amp -?
b)which wire goes to op amp +?
c)does an op amp needs to be supllied to work?And if so,with what voltage?

I don't fully understand how you zeroed out your meter, but I'm concerned that you may not have done it in a way that will provide linearity and accuracy. The opamp does need power, and you can't just use the opamp with no additional circuitry. It really sounds like you are new at this; - no offense intended.

There is a limt to how much input I can provide right now, since I'm tied up with a few things. However, I slapped together a quick schematic and recommended parts for this. There are a number of ways to approach it and many different parts could be used. So, this is just a representation of what my first attempt would be, if it were my project.

Hopefully, other people can improve on this by correcting any mistakes, or recommending parts that are more commonly available. The schmatic should make it clear how the meter needs to be hooked up to the reference voltage and the output of the opamp, just as I recommended before.

[levangram]

This is my schematic.at your right is the digital panel meter.Adjusting the pot,gives me zero voltage at zero magnetic field.if i leave it this way,it will show me the voltage difference under the presence of a magnetic field.so i need to multiply it with 0.4 before getting into the panel meter..

[steveb]

Originally Posted by levangram

This is my schematic.at your right is the digital panel meter.Adjusting the pot,gives me zero voltage at zero magnetic field.if i leave it this way,it will show me the voltage difference under the presence of a magnetic field.so i need to multiply it with 0.4 before getting into the panel meter..

OK, I think I understand what you are doing. It looks like you are powering your hall sensor with 4.5 V? This seems low to me, but it really depends on the sensor. I would think you want at least 5 V to have equal plus and minus range of 2.5V.

Another issue is that you are calibrating/zeroing off of the supply voltage which is not very accurate. Any change in voltage due to loading, or heating will throw the calibration off. This is why a voltage reference should be used. The Hall sensor has its own voltage reference internally set to 2.5 VDC for accuracy.

These are just recommendations. The complexity of implementation depends on your desired perfomance specificaitions and on the quality of the power supply you are depending on for calibration.

[levangram]

The sensor characteristics refer to supply voltage from 4.5-12V.i use 4.5V because that's the battery that i have plenty of at home!
I zero off the suplly voltage with a pot,because actually null voltage at zero magnetic field is 2.38-2.4V,not 2.5 exactly.I thought i could to it with more accuracy and that it would be more flexible at the adjustment.
After all,i'm just working on hall effect theoretically.I build this magnetometer with the sensor just for my own use,thought it would be nice to try something like this!
So,to sum up..With my way if i put
-the hall output then R1 in Vin+ of the op amp
-the wiper of the pot in Vin- of the op amp
-the output of the op amp at V+ of the digital panel meter
-the wiper at V- of the digital panel meter
and supply the op amp with 9V....I think it's ok!(??)

[steveb]

Originally Posted by levangram

The sensor characteristics refer to supply voltage from 4.5-12V.i use 4.5V because that's the battery that i have plenty of at home!
I zero off the suplly voltage with a pot,because actually null voltage at zero magnetic field is 2.38-2.4V,not 2.5 exactly.I thought i could to it with more accuracy and that it would be more flexible at the adjustment.
After all,i'm just working on hall effect theoretically.I build this magnetometer with the sensor just for my own use,thought it would be nice to try something like this!
So,to sum up..With my way if i put
-the hall output then R1 in Vin+ of the op amp
-the wiper of the pot in Vin- of the op amp
-the output of the op amp at V+ of the digital panel meter
-the wiper at V- of the digital panel meter
and supply the op amp with 9V....I think it's ok!(??)

OK, good luck and have fun. The best way to learn is hands-on.

[levangram]

Thanks a lot steveb,you've been of great help for me!
One last question if you don't mind.The op amp supply of 9V is ok or do i have to use a different suplly?

[steveb]

Originally Posted by levangram

Thanks a lot steveb,you've been of great help for me!
One last question if you don't mind.The op amp supply of 9V is ok or do i have to use a different suplly?

It all depends on the OPAMP you choose. The one I recommeded works from 1.8V to 24 V. You need a rail to rail opamp in this application, and you should carefully review the datasheet of the part you choose.

There are potential issues running directly off the battery with no regulation, but that gets into higher level concepts. If you use a power supply filter capacitor near the chip, you should be ok given the simplicity of the circuit. If you end up seeing oscillations, then report back and someone will guide you further.