# potentiometer circuit

#### THOMAS

Joined Jan 9, 2004
2
A potentiometer series circuit contains 2 resistors either side of a slidewire. The slidewire resistance is 20ohms and the supply voltage is 1.38V. If the maximum & minimum tap-off voltages are 9.0mV & 33.0mV respectively, how can I determine the values of R1 & R2??

#### Davis

Joined Jan 5, 2004
13
Well if I'm understanding your correctly (just look at the diagram below) I would do this.

Part #1)
You know that at the potentiometer (POT) lowest position it's going to produce 9.0 mV drop accross R2 and therefore you get the equation 0.009V = I * R2.

Part #2)
You know at the potentiometer's highest position there would be a +1.38V - +0.033 Volt drop across R1, which gives you the equation +1.347V = I*R1

Also, there is a +0.033V across the pot and R2 which gives you the equation +0.033V = I * (R2 + 20ohms), you have R2 + 20ohms because that's the total resistance to ground from the highest position of the pot, which is pots resitance + R2

Part #3)
From these two equations solve out for I and R2 by pluging one into the other
0.009V = I * R2.
+0.033V = I * (R2 + 20ohms)

From this equation and using the current found in the previous equations solve for R1
+1.347V = I*R1

I hope someone else takes a look over this I could have easily made a simple mistake, however this is the way that I would approach this problem

- Matt

Then
+1.38 V
\ R1
/
\
/
|
|
|
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\ 33.0mV Max resistance
/ 20ohms Max resistance
\ <-------
\
/ 9.0mV Minimum resistance
|
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\ R2
/
\
/
GND

#### mozikluv

Joined Jan 22, 2004
1,435
:huh: hi,

pls. try to review your Ohms Law or Kirchoffs Law. the answer is there. 