scott wrote:
>> Well, as I say, I started by wiring up one NAND gate, a pair of 
>> switches and an LED. What *should* have happened is that the LED 
>> lights up unless you simultaneously press both switches. What 
>> *actually* happened was completely different. :-/
> 
> How did you wire up the switches to the inputs? You can't just use a 
> connect/disconnect switch to the V+ line, because when it is 
> disconnected the input will be "floating" and probably float high.  You 
> need to either add a pull-down resistor or wire up a switch to connect 
> between 0V and V+ alternately.
> 
> How did you wire up the LED? LEDs operate depending on current, not 
> voltage, so you usually need a resistor in series to fix the current.  
> Did you also check that the IC could source/sink enough current to drive 
> the LED?

.......see, now, I went into digital electronics to precisely to *avoid* 
this kind of craziness! >_<

Take a look at a diagram such as this:

http://upload.wikimedia.org/wikipedia/commons/a/a9/Full-adder.svg

How many resistors can you see? Because I count NONE!

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