How should I connect a separated 5 V source to an Arduino connected to a RAMPS board I'm going to add a Raspberry Pi to my printer, which requires a 5 V source. I want to take this opportunity to also power the Arduino with that same source, as dropping 12 V -&gt; 5 V is a quite big waste. I know the electronics don't consume much power, and the regulator can handle the heat, but why not?
I want to know how can I safely do this. Is it sufficient to just bent the pin from the RAMPS to the Arduino's VIN?
I'm also using TMC2209 stepper drivers. According to this: https://learn.watterott.com/silentstepstick/pinconfig/, these requires the 12 V line to turn on before and turn off after the 5 V.
I wonder if this is true, as I haven't seen this anywhere else.
I would not recommend changing Arduino powering.
You can either do as you say and power Arduino by giving it regulated 5V to Vin, but then the ATMEGA2560 still will be powered through the 5V voltage regulator. The voltage regulator (NCP1117ST50T3G) needs to be supplied with 6.5V to give out regulated 5V. So you will be powering the Arduino with some 4V, which might work, but it will be less reliable. But it is electrically safe.
Second option is to power Arduino through it's 5V pin. That is less safe, because the voltage regulator might have an over output-over-voltage-protection that will to load or short-circuit the 5V until it is 5.000V.
Regarding TMC2209. I have not seen any documentation that has any opinion on what order it shall be powered up and down.