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mosc
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Joined: Jan 31, 2003 Posts: 18197 Location: Durham, NC
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Posted: Mon Feb 11, 2008 11:13 am Post subject:
On using one logic family Subject description: Thinking out loud - general principles |
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Before starting a Lunetta, it's a good idea to consider standardizing on using on logic family. We can discuss this ad nausium, but let me state a few points as general principles based only on experience.
CMOS is the logical choice because:
CMOS is very forgiving to power supply ranges. Usually, you can use virtually any DC voltage source you have.
CMOS is low-power by nature. CMOS only uses power when the logic changes from one state to another. Since our circuits will ususally clock at low frequencies (audio is very low frequency compared to usual logic rates).
TTL and others draw power constantly, so not a good choice.
The CMOS 4000 series is a good choice for standardizing because parts are cheap and readily available. 4000 logic can almost always work interchangeably with the 74C000 series, just in case. 4000 can also drive TTL in some cases as well.
So, based on the suggestion by Bugbrand himself, I think 4000 is a good logic family to start with here.
Comments welcome... _________________ --Howard
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blue hell
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Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
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Posted: Mon Feb 11, 2008 12:18 pm Post subject:
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And one CMOS output can drive many CMOS inputs (even when some conditioning input resistors are present), whereas for TTL an output drives around 10 inputs or something. _________________ Jan
also .. could someone please turn down the thermostat a bit.
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bugbrand
Joined: Nov 27, 2005 Posts: 846 Location: Bristol, UK
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widdly
Joined: Jun 25, 2007 Posts: 268 Location: singapore
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mosc
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Joined: Jan 31, 2003 Posts: 18197 Location: Durham, NC
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Posted: Thu Feb 14, 2008 2:57 pm Post subject:
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TTL is really not as good for CMOS in these applications. I think 4000 series is the way to go, but if there are better choices, we're all ears. _________________ --Howard
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Fri Feb 15, 2008 1:29 am Post subject:
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I'm all for 4000 series.
With a 100nF across the power supply pins, 100K to ground on all inputs, and a 2N3904 buffered LED on every output, are all chances of static problems quenched? _________________ What makes a space ours, is what we put there, and what we do there. |
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mosc
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Joined: Jan 31, 2003 Posts: 18197 Location: Durham, NC
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Posted: Fri Feb 15, 2008 9:05 am Post subject:
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No all chances of static damage, but lets try it out and see what happens.
I would prefer to tie inputs up to Vcc with a resistor, instead of ground. The reason is that if you touch the input thru a patch cable to the grounded front panel, you get a way to "play" the circuits directly "by hand". But either way is OK. _________________ --Howard
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CJ Miller
Joined: Jan 07, 2007 Posts: 368 Location: 127.0.0.1
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Posted: Tue Mar 11, 2008 1:46 am Post subject:
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Emitter-Coupled Logic is the wave of the future!
;]P |
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mosc
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Joined: Jan 31, 2003 Posts: 18197 Location: Durham, NC
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Posted: Wed Mar 12, 2008 1:48 pm Post subject:
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CJ Miller wrote: | Emitter-Coupled Logic is the wave of the future!
;]P |
I know a guy that has over 100 patents for ECL. He was a world authority on the subject. He ended up designing CMOS microprocessors... _________________ --Howard
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CJ Miller
Joined: Jan 07, 2007 Posts: 368 Location: 127.0.0.1
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Posted: Fri Mar 14, 2008 7:32 pm Post subject:
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mosc wrote: | I know a guy that has over 100 patents for ECL. He was a world authority on the subject. |
That's amazing! I was only half joking about ECL being The Next Big Thing because of how the industry largely ignored it, but I bet an ECL Lunetta would be quite distinctive! I don't think I am ready for that challenge yet myself.
Quote: | He ended up designing CMOS microprocessors... |
Alas... Well, I've got no credentials whatsoever, so as a result nobody has ever hired me to do anything even remotely interesting. But I won't let it stop me from trying. |
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