what PNP transistor to use

[masseyjeremy]

I plan to try this project out. I'm new to PNP transistors. Can you help me know which one I should buy for this?

[swehner]

Hey, basically any transistor is fine to use for these low power applications. It's basically just to not drive the LEDs directly from the Arduino (even though you could porbably power them directly).
You can find sample schemas on other sites - eg. here is a NPN config with a popular and cheap transistor: https://www.petervis.com/Raspberry_PI/Driving_LEDs_with_CMOS_and_TTL_Outputs/Driving_an_LED_Using_Transistors.html
Here are some other recommendations: https://www.baldengineer.com/the-best-4-transistors-to-keep-in-your-parts-kit.html
I guess it depends a bit on where you're going to buy them...

[masseyjeremy]

Thanks for the response. Your BOM list mentioned a PNP resistor. So it can be PNP or NPN? I googled the difference and found this: "The main difference between the NPN and PNP transistor is, an NPN transistor turns on when the current flows through the base of the transistor. A PNP transistor turns ON, when there is no current at the base of the transistor." So I just want to make sure I get the right type and dont break something. :) EDIT: Looking into this more, I think i understand it better. It looks like if I follow your wiring diagram, I'll need a PNP transistor, since it looks like the LED load is on the collector side between the transistor and ground.

[swehner]

So, as the NPN for a LED driver is the more common setup, I've updated the schematics to use an NPN transistor and I've updated the parts list.
I think the most common one you'll find is the BC548, although there are several other cheap alternatives!
You can see some here: https://en.wikipedia.org/wiki/BC548
I'm gonna resolve the Issue, but feel free to reopen in case you have any more questions!
Thanks!