Jan Panteltje said:
Yes those will work, but then require 4 caps and 4 resistors at least.
With 4 inputs, 4 outputs, 2 power, a 14 Ppin PIC will do, and have prosessing
to spare that could possibly be used for something too.
Like for example a 16F505
http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en020096
NO external components needed, use internal RC oscillaor.
You can use 4 port interrupts and look in the interrupt routine which
one it was, and start a counter.
Main routine can do software increment of the counters and set outputs
after so many ms, with quite a high accuray.
There are many other ways to do it too.
Why keep all that antique analog stuff around?
Because it works? OTOH, changing the timing in an analog circuit is
difficult if it means modifying a lot of components on a lot of
boards. If you go analog, you must be sure it is right before going
into production. Which is not necessarely a bad thing because it
forces you to really think about what you're doing.
I recall designing a device and using a GAL16V8 for some simple logic
functions (including some timing). I used an extra 74HC14 to have
schmit-trigger inputs for the RC timing networks. Having something
programmable in a circuit can help to implement those last-minute
changes some customers like to make.
But... using a PIC is a really bad idea. I never was a fan of PIC
controllers based on what I've seen being made with PICs and the specs
from Microchip. Unfortunately one of my customers has a product for
which the PIC 16Fxxx firmware needs to be rewritten by me. Throwing
out the stock is just too expensive. The PIC processor's architecture
is even worse than I thought. Multiple memory banks, weak instruction
set. I need to jump through a lot of hoops to write C code for it and
work around the flaws in the hi-tech compiler. Can't even re-use
existing C code because pointers don't work well with multiple memory
banks. Having all data global is the most convenient. Altogether it
costs a lot of extra development time (=money). I start to wish they
had used an 8051! The PIC really is a dead-end around the next corner
if you want to get some serious work done.