Hall sensor range limiter

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Freezingmoon

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Hello,
I have an hall sensor that gives me an output from 0 to 2,5V. This sensor is connected to an USB board and is read like an analog axis, and there is another sensor that is exactly the same connected in parallel to the first one. Basically, I can modify the same axis from two different places.
This works great for my use, but I need to adjust the range of only one sensor using a pot, for example, if I set the pot to 50% of its value, the USB board will only read variations from 2,5V (max value) to 1,25V. I tried to place a pot in series of the hall sensor output and this works okay, but looks like I need a pot with a value of 600/700ohms that its hard to find in the form factor I need. Any suggestions? Do I need a more complex circuitery?
Thanks in advance!
 

Thanks for the reply. Can you explain a little better please? Wich value?
 

Freezingmoon said:
Can you explain a little better please? Wich value?
Click to expand...

With a parallel resistor of 2kΩ to a 1kΩ pot you get a total resistance of 667Ω : Rtot = (R1*R2)/(R1+R2)
 
erikl said:
With a parallel resistor of 2kΩ to a 1kΩ pot you get a total resistance of 667Ω : Rtot = (R1*R2)/(R1+R2)
Click to expand...

Hi, I almost forgot about this post. I tried your solution but I have the exactly same results. Do I need to use an op-amp comparator of some sort?
 

crutschow said:
No you shouldn't need an op amp. Post the circuit of what you are trying.
Click to expand...

Hi, attached the schematic.
With the potentiometer I'm trying to change the range of HALL2, but as I said in my previous messages it doesn't work well.
For example if the sensor give me an output from 5V to 0V (I'm making numbers now since in my application the values are different, I can measure them if needed), and I set the pot at let's say half way, the USB board will read an input from 2,5V to 0V. If I set the pot at the min value, the USB board will read variations from 5V to 0V. If I set the pot all the way up, the USB board will read 5V. Hope I made it clear what I need
 

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Freezingmoon said:
... another sensor that is exactly the same connected in parallel to the first one. Basically, I can modify the same axis from two different places.
Click to expand...

Basically, it's not a good idea to connect 2 outputs together, as they'll fight against each other. With 2 separate voltage dividers divide down their output voltages to the range you need (e.g. 2*4.7kΩ to get 2.5V from the 5V max. input). Then connect a pot (10 ... 100kΩ) between these 2 divider points and connect its tap to the USB input.
 

SunnySkyguy said:
It all depends on which type sensor is used and desired mixed output voltage ratio.

Sensor P.N.=?
Is it a current source or voltage source or voltage source with a series resistance?
Click to expand...

I'm using the Allegro A1302: https://www.allegromicro.com/~/media/Files/Datasheets/A1301-2-Datasheet.ashx

- - - Updated - - -


Thanks, do you have any schematic/reference? I'm sorry but I can't draw schematics from scratch...
 

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