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Make potentiometer more sensitive.

Pommie

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Most Helpful Member
Thread starter #1
I want to make the middle of a pot more sensitive. The pot will be connected between 0 and 5V and when the pot is centered the output will be 2.5V. I want to make the bit either side of center to be extra sensitive such that 3V on the pot gives 5V out and 2V on the pot gives 0V out. So, 2-3V in maps to 0-5V out.

Suggestions.

Mike.
 

dknguyen

Well-Known Member
#2
Maybe two comparators that each drive a transistor to short the wiper to the rail/pot end? Unless you can find a transistor output comparator like the LM311.
 
Last edited:

Pommie

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Most Helpful Member
Thread starter #4
Perfect. Just emulated in LTspice and it does exactly as asked.

Thanks,

Think I've got a few LM358 that should surfice.

Mike.
LTspice.png
 

MikeMl

Well-Known Member
Most Helpful Member
#5
Try a single opamp with a non-inverting gain of 5.

: t3.png

The independent variable of the simulation is pot position (x-axis). The dependent variables plotted are V(wiper) and V(out).

Gain is 1+200K/(100K//100K) = 1+(200K/50K) = 1+4 = 5 centered on 2.5V , so 3Vin = 5Vout and 2Vin = 0Vout.

Try it for any reasonable value of pot resistance...

It does depend on the opamp being rail-to-rail out, which an LM358 is not. If all you have is LM358s, then you will need more than a single 5V supply.
 

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Pommie

Well-Known Member
Most Helpful Member
Thread starter #7
I assume the LM358 isn't suitable due to the max output voltage being Vsupply-1.5 which would only allow me to measure inputs from 2-2.7V. This will probably do for my situation but just in case I can get hold of an LMC6482 locally which should manage the full range.

Mike.
 

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