So why use a ATtiny2313 and not an ATtiny85, when a ATtiny85 seams to be the more logical one to use?
The ATtiny2313 has many more pins than this project could ever use. Over kill on the pin count.
That also makes it psychically bigger that say a ATtiny85. 20 pins instead of just 8.
It doesn't have the byte capacity of a ATtiny85. ATtiny2313 has 2K bytes verses the ATtiny85 8K bytes.
Like most everything it comes down to cost. The ATtiny2313 is the cheapest micro-processor i can get in my area, when shipping ect is factored in.
ATtiny2313 is $1.75 USD. Where as an ATtiny85 is $4.50 each if i buy 2. ATtiny2313 PDF