Raspberry Pico 2N22A2 NPN BJT LED Example. Where the Base is really just a GPIO pin set high (1) which passes 3.3V to the base. This is to allow lighting an LED to approximately 20mA with only using .4mA from the GPIO line. Individual GPIO lines on the Pico are recommended not to exceed 12mA. The voltage source on the collector is the "true" 3.3out connected to + on your breadboard power rail most likely. Assumes a 1.6 forward voltage drop on the LED. You can try to fine tune using different resistor values and LED's with different voltage drops. Of course like all NPNs values are never exact due to heat ect... Most 20mA LED achieve no noticeable difference in brightness from 16mA to 20 mA.
