www.piclist.com/techref/index.htm?key=formula+unbalanced

Oops - mixed up Rx and R2 - let's try again...

Vin

R1 R2

+--|--

| +-- Vout

R3 Rx

0V

Treating each side as a potential divider : Vout = Vin(R3/R3+R1) - Vin(Rx/Rx+R2)

Vout = Vin((R3/R1+R3) - (Rx/Rx+R2))

We want the answer for Rx given the Vout/Vin ratio- call this ratio V,

so this becomes :

V = (R3/R1+R3) - (Rx/Rx+R2)

..and this is where my algebraic ability grinds to a halt..!

So the question is how do you juggle this to get either :

Rx = function_of(V)

Or (better, if possible)

Rx/R3 = function_of(V)

..and can it be simplified further if R1=R2 ?

--

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