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Thursday, 24 May 2012

Resistor Substitution Box

I built this after finding some cool push wheel edge switches on eBay from a really cheap Chinese seller, I honestly thought they would be crap but over a year later it is still working as new.
to make it as accurate as possible I measured each resistor with my just calibrated Fluke 87 III on hi-res mode and my old Fluke 77 for second opinions sake. so that it isn't just in a tolerance - it is exact and I also got resistors that change value as little as possible over temperature ranges. I know things don't need to be that accurate but I'm a bit weird that way. it's kind of a "confidence in your tools" thing.

anyway although I've tried to get pictures of how I made this thing with a crudely drawn picture, I'm not sure if it's clear as to how I did it.

Also it's probably worth me mentioning that with each decade you use the resistor value you're multiplying by
so the first one (on the right) is 10 1ohm resistors, the next one is 10 10ohm resistors, next 10 100ohm resistors and so on.
feel free to comment and ask for any further help should you need it.

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