>> And then I got stumped by the fact that the gates don't appear to do 
>> what the diagrams suggest they should...
> 
> In what way?

The 7400 is a quad 2-input NAND gate. In other words, it's a box with 
four NAND gates in it.

What's supposed to happen is that you connect pins 1 and 14 to a power 
source, and the remaining pins are grouped into 3s. Each group is the 
connections for a single NAND gate. When the inputs aren't connected, 
the output pin is at logic high. When you connect both of the input pins 
to the (+) rail, the output should go low.

...except this doesn't seem to happen. I swear to God I built circuits 
like this when I was a kid, and it worked. But when I tried it as a 
teenager, it wouldn't work for toffee. No idea why.

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

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