If your external stuff is not very power-hungry (no motors or large relays or the like), you can use the 5V pins on the GPIO header to power external devices, through the Raspberry Pi, from its USB power supply. I'd recommend the "official" 5V@5A USB-C supply for this.
My warning was about the GPIO signal pins, which can't tolerate voltages about 3.3V! Often (not always) a 3.3V output can control 5V logic inputs, but take care there are no pull-up resistors to 5V or anything else that might pull the pin too high. If in doubt, use a level shifter or buffer. Obviously it's not an issue for simple things like switches.
The MCP23017 I/O expanders can be run at 3.3V (directly) or at 5V (through a I2C-compatible level converter), and you can even get boards that have the level shifter built in and are 5V safe.
That serial LED driver chip should work for common-anode LEDs -- connect VCC to the 3.3V rail and VLED to 5V. (BTW, although it would make the wiring a bit messier, you might want to drive R, G and B channels from different chips, so you can adjust their current-setting resistors to get a nicer white balance? Just a thought.)
My warning was about the GPIO signal pins, which can't tolerate voltages about 3.3V! Often (not always) a 3.3V output can control 5V logic inputs, but take care there are no pull-up resistors to 5V or anything else that might pull the pin too high. If in doubt, use a level shifter or buffer. Obviously it's not an issue for simple things like switches.
The MCP23017 I/O expanders can be run at 3.3V (directly) or at 5V (through a I2C-compatible level converter), and you can even get boards that have the level shifter built in and are 5V safe.
That serial LED driver chip should work for common-anode LEDs -- connect VCC to the 3.3V rail and VLED to 5V. (BTW, although it would make the wiring a bit messier, you might want to drive R, G and B channels from different chips, so you can adjust their current-setting resistors to get a nicer white balance? Just a thought.)
Statistics: Posted by njh — Mon Jul 07, 2025 9:30 am