No, I haven't tried it.Do you have the source code for the ATtiny? If so, can you substitute a different AVR for the ATtiny45? It's very likely you can... with caveats.If you don't have the source, the object code will NOT work.Frankly, the ATtiny and ATmega series have quite a few differences internally. Not enough to prevent attempting the substitution, but the default clock, internal registers and such vary.But why would you use a 16K chip to replace a 4K chip, if the # of I/O lines were the only issue? Why not use a cheaper ATmega48 or ATmega88?That's like saying: "Can I replace my MiniCooper with a Cadillac Escalade?" The answer is maybe--if you can afford the extra expense, and if it's not too big for the job, physically.