Math help

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hi!

i`m bad @ mathematics, , not in electronics either, feels should possible knowing pullup resistor have, calculating pulldown resistor must be, if can measure regulated voltage in middle.
is it?

thanks reading! :)
//mikael

you right!

if resistors are  2:1  voltage divided  2:1

example

+5v  ----[5k]----x ----[ 10k] ---- 0v

x = (5v-0v) / (5k + 10k) * 10k = 5/15*10 = 50/15 = 3.3v

+12v  ----[20k]----x ----[ 10k] ---- 0v

x = (12v-0v) / (20k + 10k) * 10k = 12/30*10 = 120/30 = 4.0v


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