[sdiy] A little OT, Begging a hand

[Veronica Merryfield]

I wonder if anyone might be able to help me out on what I was hoping was a simple problem.

I have the following resistor network (ascii art follows so you'll need a fixed pitch font selected)

 V1
 |
 \ 
 / R1
 \
 /
 |    R4        R6   
 |--/\/\/\----/\/\/\----- Vout
 |          |         |
 \          \         \
 / R2       / R7      / R8
 \          \         \
 /          /         /
 |    R5    |         |
 |--/\/\/\--          |
 |                    V3
 \ 
 / R3
 \
 /
 |
 V2

I can set each of V1, V2 and V3 to either +Ve, GND or OC independently, although not all combinations are useful, and I can measure Vout. R1+R2+R3=K, about 600 ohms. R1=R6 and R2=R7, R4 and R5 vary between about 1K and 500K and R8 is fixed at 2K2 although this can be changed.

I want to set a number of input combinations and measure Vout from each in the hope that I can determine R1, R2, R3, R4 and R5 with some simultaneous equations. 

My attempts have been a bit of a failure and I think I am missing something so I was hoping someone here might be able to help me.

For reference, this is the equivalent circuit for a sensor I am working with on a music controller project.

Veronica