Fundamentals Friday Topic - Basic Logic / 74 series usage for hobbists

[nixfu]

I am pretty experienced with passive components and using them in my designs.  But, I have not had anything to do with logic/74 series stuff since the introduction I got in university.

What would be maybe a good idea is giving some introduction for new guys/hobbists, and translating some of that into where they might use them in the real world in their own hobby project designs. 

Right now in my own hobby designs, I always reach for a micro whenever I need logic etc.. maybe I should use more discrete logic in my deigns (simpler, cheaper etc), or maybe I could use some added 74 stuff as "glue" for my projects that do involve a micro.

Not many hobby electronics people ever talk about using 74-logic components in their designs, so this is definitely a needed topic to cover.

[rob77]

i love 74xx logic, but the time of those is over clpd & fpga is the future - even for hobby projects.
makes no sense to start with 74xx logic unless you're already into it

[PepeK]

74xx family or CMOS 40xx family can teach you some basics like what are AND, OR, JK, D ...
I do not see a real usage of them now except of a level shifting (74 AHC 245 ...) or shift register if you do not enough pins on a CPU for LCD.
CPU is configurable and cheap - Atmel 8 bit for 1 USD, on chip programming - for 74 based logic everything is hardwired.
FPGA consists of those basic logic elements like gates and D latches and again it is reconfigurable via development tools.

[nixfu]

Wouldn't getting into a little discreet logic make the transition to CPLD and FPGA that much easier?

As a hobbyist it would be find to use a little 74-logic once in a while, and certainly the more comfortable you are with those, the easier it might be to move to FPGA later on, or use a micro that has a some on-board gates etc..

Also, us hobbyists should take advantage of all the great components that came before us and learn just how useful they can really be for only $.025 US each.

[bwat]

Wouldn't getting into a little discreet logic make the transition to CPLD and FPGA that much easier?

I was taught digital design with 74 series chips  about 25 years ago and I relearned it all again this year. Some observations:
1) The book I used goes from assuming the reader knows nothing and goes all the way up to CPU design techniques and doesn't mention the 74 series chips once; there's no need to.
2) Digital design with FPGA is much more convenient. Constructing a reasonably sized circuit is so much faster as you're not looking for the right chip, then pushing it onto your breadboard, then wiring it up, etc.
3) The 74 series components constrain your designs. People implementing CPUs with 74 series logic build 4-bit or maybe even 8-bit designs if they have more time and physical space. With FPGA implementation, it takes about the same amount of time and physical space implementing a 32-bit design as it does a 4-bit design.
4) I can work anywhere with FPGA. My smallest laptop (EeePC) and my smallest FPGA board (DE0-Nano) fit into any bag. This is either completely unimportant or very important for you.

I don't miss the 74 series chips, not for the sort of stuff which I'm working on.

[David Hess]

I do not see a real usage of them now except of a level shifting (74 AHC 245 ...) or shift register if you do not enough pins on a CPU for LCD.

I/O expansion, level shifting, and simple mixed signal circuits are the obvious uses but another place programmable logic has trouble is where low jitter is required.