Some tutorial about using UART as a serial console suggested connecting USB-UART adapter power line to GPIO Pin 4 (+5V), and I did so, and it seems OK. But maybe I'm doing it wrong and should connect to Pin 1 (+3.3V)?The SoCs used on the Raspberry Pis have two built-in UARTs, a PL011 and a mini UART. They are implemented using different hardware blocks, so they have slightly different characteristics. However, both are 3.3V devices, which means extra care must be taken when connecting up to an RS232 or other system that utilises different voltage levels. An adapter must be used to convert the voltage levels between the two protocols. Alternatively, 3.3V USB UART adapters can be purchased for very low prices.
Another question is https://pinout.xyz/pinout/pin1_3v3_power says:
. So, if I understand it correctly, the board gives power to connected peripherals. But if I connect USB-UART adapter to PC without powering on the board, it still powers on and tries to boot (although fails with low-power-supply error message). Thus it appears not to give power, but to receive it from the connected device. Does it work in both directions?All Raspberry Pi since the Model B+ can provide ... up to 500mA to remain on the safe side. ...Still, you should generally use the 5v supply, coupled with a 3v3 regulator for 3.3v projects.