Hi I've got a Raspberry Pi, that's 3.3V device, and a Nextion display, which is a 5V device. They are talking over UART. Obviously RPi's UART RXD link can be damaged if connected directly to the Nextion display output.
Long time ago I read somewhere an explanation that it's not the voltage that damages the lower voltage devices but the current that can flow through. And therefore for input pins like this it's enough to put a big enough resistor between the 5V output pin and 3.3V input pin to limit the current and be done with it. No resistor dividers, no level shifters, just a single resistor. Makes sense to me, but I can't find the original article for reference.
How can I tell what value should such a resistor have?
a lot of noob-targeted 3.3v hobby electronics are 5v tolerant anywayblatantly untrue. The four biggest, 3.3V arduinos, esp8xxx, msp430 launchpads, and raspberry pis all lack 5v tolerant inputs. \$\endgroup\$