>> ....which is why I'd rather work at the gate-level. ;-)
>>
> 
> The problem is that digital electronics are based on analog circuits.  A 
> lot of digital circuits can be wired up with out knowing anything about 
> analog, but when something doesn't work as you expect, you might quickly 
> get lost.

Yeah, this is the thing. I had assumed that the digital devices you buy 
in the shop are carefully designed to behave in a simple, predictable 
mannar, even though their internal construction is a tangle on analogue 
devices. I thought you could just treat a 7400 as a black box. 
Apparently not...

> And as you have found out with LEDs, even when you think you are only 
> dealing with digital, you are dealing with analog as well.

The LEDs actually worked just fine. It's the gate driving them that 
didn't do what it was ment to.

> Even something as simple as a button or switch can cause problems.
> When you close the contact there are literally thousands of connections 
> made and broken in the very short time before the contact is completely 
> closed.  If you have a counter, it might count 4 or 5 on each button 
> press, not just one.

I wouldn't find this surprising. Rather, to be expected.

> That's what debounce circuits are for, but they 
> can be analog - go figure.

Presumably a debounce circuit is merely a low-pass filter?

> Don't try to build a rocket ship - build something simple.

Heh. I got stuck just trying to get a truth table out of a logic gate. :-S

> Get a book that doesn't just say hook this wire here and there, but that 
> actually goes through how it all works.
> The CMOS Cookbook I pointed out earlier is a good book in that reguard.

...does it matter that I'm using TTL?

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