help with resistors

This is part of a thermostat. The problem is that the pot is to touchy. Just touching it throws the temp off 1 degree. I need to make it less touchy. I can sacrifice the 70-106 degree range and go with 95-105. I have looked in my books and can't find the equation to figure the changes that i need to make. I know that the 1.5K is the Temperature max and the 1K to ground is the Temperature minimum. The pot has a value of 1K. Do i swap the pot for a 500R and make the R12 a 1.5K? Can some one tell me the formula. I found the Vout=Vin x ( R2 / R1+R2) but that's as much as i can find for this application. At a guess useing this formula does that me the the voltage value for each extreme of the pot dial would be from 3.42V-5.14V? Thanks.

Is a multi-turn pot not an option?

worse case scenario.

R14 = 1750Ω and R15 = 1250Ω.

Algebra works every time. Two equations in two unknowns.

MikeMl said:

R14 = 1750Ω and R15 = 1250Ω.

Algebra works every time. Two equations in two unknowns.

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Thanks mike. What equation did you use? Remember, i'm new to this stuff.

cbiblis said:

Thanks mike. What equation did you use? Remember, i'm new to this stuff.

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Kinda rough. I learned how to do this in High school in 1959

MikeMl said:

Kinda rough. I learned how to do this in High school in 1959

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Thanks, that is exactly what i needed to know.

Ok. I understand. From my calculations. The old configuration ranged 3V-6.86V. With the alteration to the R1 and R2 i show a new range of 5V-6V. Which is to tight of a range. So i need to use a 750 pot which will give me an r14 @ 1625 & R15 @ 1125 giving me a range of 4.91V-6.42V which is perfect for my application. Thanks again mike.

Oops. There isn't a 750 ohm pot available from my suppliers in a dial type. Is there a way to make a 1k pot into a 750 with resistors?


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(Sorry, that was a stupid question. I guess that a resistor in parallel with the pot will work.)

Yep, that will work. Another trick would be to keep the 1000Ω pot, but make the two end resistors higher. That will reduce the current through the divider a bit, but that likely doesn't matter. Many ways to skin a cat.

MikeMl said:

Yep, that will work. Another trick would be to keep the 1000Ω pot, but make the two end resistors higher. That will reduce the current through the divider a bit, but that likely doesn't matter. Many ways to skin a cat.

Click to expand...

I think that i have my solution to my problem. I will put a 3k resistor on the 1k pot to bring it down to 750, then make the r2 a 1.2k and the r1 a 1.8k. The value at the set point is 5.27V. My range will be 4.8V-6.2V. I'm so excited that i learned something that i think that I'll apply it to all of the E24 resistor values and make a graph. Someones probably already done it but it will help me remember.