> Well anyway, FWIW, the IC managed to drive the LED just fine. (I bought 
> special 5V LEDs; apparently normal ones take roughly 3V.)

"normal" ones work at all sorts of voltages, it even varies from piece to 
piece quite significantly.  But you never drive an LED directly by applying 
a fixed voltage, you always drive it by regulating the current to a fixed 
amount (like 20 mA or whatever).  Adding a series resistor to a raw LED is a 
quick and crude method of fixing the operating current.

> You think using a 2-pole switch with the poles connected to each of the 
> power rails will do it?

Yup, or just connect a high value resistor (eg 10 or 100K) between the input 
and the other power rail - so you have your switch arranged like this:

http://www.seattlerobotics.org/encoder/mar97/basics4.gif

That way, when the switch is open, the input is connected to 0V, and when 
it's closed it is connected to V+.

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