Hall sensor range limiter

[Freezingmoon]

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!

 

[crutschow]

Why does the pot need to be 600/700 ohms? If that's the value after adjustment then just us a 1k ohm pot.

 

[Freezingmoon]

Why does the pot need to be 600/700 ohms? If that's the value after adjustment then just us a 1k ohm pot.

Just don't want that around 1/4 of useless travel...

 

[erikl]

I need a pot with a value of 600/700ohms that its hard to find

Use a parallel resistor.

 

[Freezingmoon]

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

 

[erikl]

Can you explain a little better please? Wich value?

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

 

[Freezingmoon]

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

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]

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?

No you shouldn't need an op amp. Post the circuit of what you are trying.

 

[Freezingmoon]

No you shouldn't need an op amp. Post the circuit of what you are trying.

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

 

[Freezingmoon]

Anyone saw my schematic?

 

[erikl]

... 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.

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.

 

[D.A.(Tony)Stewart]

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?

 

[Freezingmoon]

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?

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

- - - Updated - - -

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.

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

 

[erikl]

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

Try this one: . For RV1 and R2 try 5kΩ or 10kΩ.