[sdiy] Followup, was A little OT, Begging a hand

[Veronica Merryfield]

Thanks to all those that helped with this.

I used my simulation to generate the results to a CSV file and imported that to Calc (Open Office Spreadsheet). By messing about with the curve fitting functions and adding some power terms and cross products, I have a solution that doesn't involve too many multiplies and yields a 2% error in R1, R2 and R3 (the positions) of which the worse ones can be cleaned up using a weighted change to bring the sum of the values to the fixed value they are known to be. R4 and R5 have errors nearer a 5% error.

I then changed the simulation to generate the positions, pressure scales and ADC values to give me the numbers needed for the target code. Plugging this in gives a pretty satisfactory result - 2 touches and 2 pressures and the errors are unnoticeable. 

Once again, thank you folks.

Veronica
 

On 2011-02-07, at 10:50 PM, Veronica Merryfield wrote:

> 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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