> Ah, OK. If you want bipolar then yes, you'll need more relays. 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+).  *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).

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