CrossRoads:
Yes, Voltage available to the LEDs will be 5V less the Vce-sat of up to 1V. If you look at the charts that complete the datasheet, there will be curves showing the voltage at different currents.
MOSFETs are better in that regard - a good low Rds MOSFET will be in the 10mOhm range (.01 ohm) and the voltage drop will be small - with 1A of current thr the MOSFET, the voltage will be V = IR = 1A * .01Ohm = .01V.
fungus:
BulldogLowell:
So, if I don't want to spend to much on a (multiple) MOS for this project, and I am only looking to pass less than 200mA through any one group of led's, the 2P2222 'old fashioned' transistor will be OK, yes?Yes.
Also a lot cheaper/smaller.
Use a 220 Ohm resistor between Arduino and transistor base, just to be sure you're saturating it.
PS: MOSFETs are 'old fashioned', too. It's just a different way to do it. MOSFETs have problems all of their own.
Read this page: BJT H
Thanks for all the help @Crossroads and @fungus, I have the led's playing nicely and the transistor seems happy (cool).
Interesting to see the led light up a bit from just touching the shielded jumper before I attached it to the 220ohm resistor.