>>> The reason it looks complicated is because you are using a 
>>> current-amplifying device (the BJT) to amplify voltage.
>>
>> Uh... does it matter?
> 
> Well yeh, that's why the resistors are needed.  Generally you want to 
> amplify voltages, not currents.

...because you don't want to actually push too many electrons around and 
warm up the wiring?

>> Let's assume that a positive potential represents logic high, and a 
>> zero potential represents logic low. Take a pair of relays connected 
>> up so that by default the circuit is closed, and energising the magnet 
>> opens the circuit. (This is easy to arrange with 3-pin switch type 
>> relays.) Connect the relays in parallel between the positive rail and 
>> the signal output terminal. Connect each input to one side of one 
>> magnet coil, and connect the other sides to the negative rail. Done.
> 
> I don't understand what is connected to the negative rail?
> 
> Don't forget that the output must be connected to either the negative or 
> positive rail (and not both!) under all input conditions.  It sounds to 
> me like in your circuit, the output will just be floating (ie not 
> connected to anything) when you charge both relays.

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. (After all, a digital 
circuit is just a circuit that has two possible states. It doesn't 
matter especially what those states are, so long as everybody agrees...)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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