Thanks for that, ElCaron, but I am not quite with you.
ElCaron:
In first order, it really does not matter (though both of your PDFs pull down, don't they?).
No. If I have this the right way round, Boxall uses pullup on the lEDs and pulldown on the switches. I use pulldown all over.
ElCaron:
I heart that with traditional TTL logic, pulling an input to LOW took more current than to pull it to HIGH, hence pullups are more common. ... You get them for free in the Arduino, since they are integrated and switchable in the AVR. So with a pullup, you can just attach a switch und do the rest in software.
Am I to understand that each output pin on my UNO has a built-in pullup resistor? From there, am I to take it that I don't need external pullup when driving an LED. I seem to remember my first excursion into LED land (not all that long ago) when the LEDs would freeze ON and the solution was pulldown resistors. That's why I have installed them since.
ElCaron:
Also, ground may be better available at the switch than 5V. Usually, everything is filled with a ground plane anyway, you don't have to break it with a 5/3.3V trace to one switch terminal.
I don't understand what you are saying here.