[sdiy] A little OT, Begging a hand

[David G. Dixon]

Hi Veronica,

Based on my reading of the network, R5 and R7 can be taken as a single
resistor, which I'll call R57.  Hence, this network has four nodes, namely
the junctions of:

R1-R2-R4 (at VA)
R2-R3-R57 (at VB)
R4-R6-R57 (at VC)
R6-R8 (at Vout)

Each node has an unknown voltage.  Simply conduct current balances at each
node, and this will give you four equations for your four unknowns.  For
example, at the first node listed above:

(V1 - VA)/R1 = (VA - VC)/R4 + (VA - VB)/R2

Repeating this process for each node will give you your system of four
independent linear equations.

Hope this helps!

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C. V6T 1Z4
Canada
 
Tel 1-604-822-3679
Fax 1-604-822-3619
 
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> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of Veronica Merryfield
> Sent: Monday, February 07, 2011 10:50 PM
> To: synth DIY
> Subject: [sdiy] A little OT, Begging a hand
> 
> 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
> 
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