>> I'm 
>> used to playing with TTL circuits where if you connect it to V+, 
>> that's 1, and if you connect it to thin air, that's 0.
> 
> Err no, in TTL with BJTs, a floating input is usually pulled up to V+ 
> inside the chip, but this is not guaranteed so your inputs should never 
> be floating (always tie unused inputs to either V- or V+).

Uh... OK. I never did that before - but hey, maybe that's why half my 
circuits didn't work?

Damnit, I thought digital electronics was just about on or off. :-/

> *Outputting* 
> a floating signal is just a disaster is normal logic (there is nothing 
> to stop some very small amount of interference driving it high), and 
> usually only used where you need to have more than one output connected 
> to the same line (eg the data bus inside your PC - each connection to it 
> should be able to output low, high, or not-connected).

You speak of "3-valued logic" with it's "Hi-Z" mode?

-- 
http://blog.orphi.me.uk/
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