Test a bi-directional 5/3.3V level shifter module.
3.3/5V level-shifting modules are quite common, as the need to interface 5V microcontrollers with 3.3V devices/sensors (or vice versa) is pretty common. Often these are billed for I²C or SPI, although they are non-specific and can be used for level-shifting any kind of digital signal. Note: yes, digital high/low signals only; they do not provide an analog scaling of voltages.
I got some of these modules from a seller on aliexpress
This circuit is a quick test of their behaviour: a switch in the 5V circuit controlling a load (LED + resistor) in the 3.3V circuit.
This is identical to the test circuit used in the BidirectionalLevelShifter project, which demonstrates the basic FET trick used by these modules.
All good! Now to put them to work…