In theory your calculations same with mine. The r2 / r1 ratio is 3 always. But it just does not work I dont know why.. Maybe the chips are really bad.hi,
If you are confident that its a adjustable, make R1 a 220R, R2 a 620R and use a 9V dc input, don't forget the 10uF across R2.
What is the 5v driving into, ie: load resistance.?
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