Thread: Resistor puzzle
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Old 17th May 2018, 12:24 am   #2
GrimJosef
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Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Resistor puzzle

Your measurements fit into three independent equations, and there are three unknowns (the resistances). So brute force algebra will get you there in the end.

I wondered whether I might get the answer more quickly by writing a little spreadsheet model of the circuit and homing in on the answer 'using my skill and judgement' to refine my guesses for the three resistor values. It took me 18 minutes to arrive at the answer including writing the model in MSExcel (other spreadsheets are available ) and raising and lowering my guesses until I was within 0.05% of your measurements. I would have hoped that I might have managed the algebra a bit quicker than that had I been wide awake. But the spreadsheet approach is less complex and so, at this time of night, is probably less prone to error.

I should also say that I used what I know of resistor manufacturers' preferred values to speed up my trials. In the end a couple of the components seem to be 1.5% and 2.3% away from what I might have guessed and the third one is 7% away. Is that what you find ?

Cheers,

GJ
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