Keep in mind here that I'm an amateur at best when it comes to this stuff. I've been playing around quite a bit with logic circuit design lately. I've amassed a pretty large collection of 7400 series ICs. And just to torture myself, I've tried to implement a few of them from the ground up. It's been very educational.
But I can't help noticing that in almost every case, I can take a big messy logic circuit, throw it away, write some pretty basic code for an AVR and achieve the same results.
Every now and then you just need a simple NAND gate. Other compenents like a BCD to 7-Segment decoder are also useful from time to time. But overall, it seems like these clunky components are a dieing breed. Am I just crazy?
No, you're not crazy. Logic mostly survives in those cases where a CPU isn't fast enough, and even then it tends to be implemented in FPGAs and similar instead of with individual gates like 74xx logic.
And the concept scales down nicely also. The Picaxe 08M chip is a 8 pin PIC chip that can do most any logic application that it's 6 I/O pins allows. It's indeed the new programmable 555 chip. Free PC IDE software and it uses a bootloader so no programmer required. http://www.rev-ed.co.uk/picaxe/
There's even a 6-pin SOT-23 PIC chip with 4 IOs.
For a while the Atmel ATtiny11 was "king of cheap", selling for $0.25 each in moderate quantity (something like 0.32 in 100 lots from digikey.) Alas, they've discontinued the part
However, your "new 555" comment serves to point out some of the weaknesses of modern microcontrollers as well. The original 555 runs off supplies from 4.5 to 16V, and supplies (or sinks) up to 200mA of current on its output pin. The inputs are as tough as nails. You won't find that sort of ... sturdiness in a microcontroller. There was an interesting discussion on Instructables about designing a digital replacement for antique door chime controllers (which are electromechanical; spring loaded solenoids with oil-filled dampers and such.) By the time you interface to the ~24VAC on inputs and outputs and supply (your standard "doorbell transformer", you've added a LOT of expense, and your circuit board size is creeping up to where it's BIGGER than the original mechanical monster. It was ... annoying.
Actually the concept is not new. I started working with microprocessors over 30 years ago. In the early 80s, Motorola came out with the 68HC11 microprocessor which had on board ram, eprom, and i/o. The who AVR concept is not new, just a different spin on it.
No one said the microcontroller concept is new, but to be the "new 555", the microcontroller has to reach a certain point WRT price, size, ease-of-use, and re-usability. Sub $0.50 and 6 pins are both things that have happened within the last 5 years or so...
"Sub $0.50 and 6 pins are both things that have happened within the last 5 years or so..."
Plus coupled with the free PC based tools that makes access to hobbyist and new comers and not just people in the industry. It's a real enabling technology that can really bring the power to the people
There are some places where discreet logic chips can be used to good advantage. Like multiplexing / demultiplexing and the like.
Also a few chips can often lighten the computational burden of a processor, especially where things have to be done in parallel. For example you can de bounce the rotor switch encoders in software providing you can service an interrupt fast enough but two logic chips do it for you. This can be important if you have many such input devices to service.
Yes FPGAs can be useful to implement such things but the continuing survival of the 74 series of logic circuits shows that they are still usefull.
I use an ATtiny45 and an ATtiny26 controller together with a CPLD module for highspeed detection of insects in-flight. Only 40 usec or 4/10.000 sec are need for the system to see if an insects is in foucus. This is an example where AVR controllers and CPLD or FPGA give the best results.
Because of my first replay no direct link now to my results are possible.
