18 Feb
2010
18 Feb
'10
3:36 a.m.
On Feb 17, 2010, at 8:19 PM, Joachim Thiemann wrote:
Crazy? I'm cheering too! It gives me great hope, seeing people
doing things like this. "Building stuff" seems to be coming back
into style. I applaud the "Make" crowd.
-Dave
--
Dave McGuire
Port Charlotte, FL
The main
problem is that those breadboard are terrible. It's not the
clock speed that matters, it's the swtiching time of the IC. Most
modern
ICs have ouptus that switch so fast that when you combine them
with the
stray capacitances on the breadboard and the relatively high
impedance
power connections, you get power and ground lines bouncing all
over the
place. Without a _good_ 'scope it's impossible to know why your
circuit
doesn't work. If you stick to 4000 series CMOS you'll be alright, but
modern 74xxx familes are pushing it. Really pushing it.
But if you're just learning high speed don't matter, even with full
computer prototypes. Incidentally, I just saw this:
http://blog.makezine.com/archive/2010/02/
building_a_cpm_68k_computer_from_sc.html
Crazy, but I'm cheering for him! Retrotastic! :-)