[TriEmbed] Question For Meeting Tonight

[Grawburg]

Many of you are aware of my traffic light project with the Raspberry Pi. I currently have 12 LEDs that are connected to the Pi through an MCP23017 I/O port expander. The Pi provides 3.3 VDC to the LEDs with 470 ohm current-limiting resistors. This combination works just fine (I'll have it with me tonight.)  But I want to also make a set-up that uses an external 5 VDC to power the LEDs; I will still use the MCP23017 to provide the additional output pins.  There are two options I am aware of and would like some comments tonight.

1. Use 12 2N3904 transistors (with appropriate resistors)
2. Use three 4-channel LTV-847 opto-couplers (also with appropriate resistors)




Thanks,
Brian Grawburg