hey, I've got 5 volts here, I can just do another 50% voltage divider to get 2.5 volts. So a couple of 10k resistors and now I had what I thought should be 2.5 volts heading into that 3v3 pin.
But that's not what I measure there.
Yeah. Welcome to Ohm's Law.
If you measure the voltage at the midpoint there with nothing else connected to the midpoint, it will read exactly half of the input voltage. But only because the voltmeter has a high impedance (resistance here), and doesn't suck more than a microamp or two.
A voltage divider (two resistors) works only for a tiny current draw. Because of Ohm's Law, a tiny current draw will still yield close to the desired output voltage. But draw more current (like.. powering a bluetooth chip with it) and E=IR says that the resulting voltage drop through the resistor will be high, leaving nearly nothing left.
Or something like that. The only way to make a resistor ladder work here is to use SMALL resistors, so that they can conduct more current with minimal voltage drop. BUT "more current" means more waste (heat) in the resistors, and that's not great either so don't do it.
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