help with resistors

[cbiblis]

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.

 

[jimlovell777]

Is a multi-turn pot not an option?

 

[cbiblis]

worse case scenario.

 

[MikeMl]

R14 = 1750Ω and R15 = 1250Ω.

Algebra works every time. Two equations in two unknowns.

 

[cbiblis]

R14 = 1750Ω and R15 = 1250Ω.

Algebra works every time. Two equations in two unknowns.

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

 

[MikeMl]

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

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

 

[cbiblis]

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

Thanks, that is exactly what i needed to know.

 

[cbiblis]

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.

 

[cbiblis]

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?


*Deleted post*

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

 

[MikeMl]

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.

 

[cbiblis]

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.

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.