/diy/ - Do It Yourself

>>1667441
>And I all this time though that SPI is a serial port...
but it is. it's just synchronous instead of asynchronous (SCK), and message-oriented instead of stream-oriented (~SS)

>>1667468
it's far from unusual for modern digital ICs of significant complexity to have a separate power domain and voltage standard for I/O banks, possibly several

>>1667480
Pic related, the zener in the feedback loop provides the offset, which unfortunately varies with the 3.3k resistor and the output voltage. for more stability, replace the zener with a TL431 voltage reference and appropriate set resistors, sketched in grey (you'll probably want one of them to be adjustable). an LM321-type opamp, or any other whose common mode input range includes ground, is fine