coin operated machine

hello friends..

i m going to make one project which is based on coin operated..
bcoz i have no path for that... from where i have to start..?

my main aim is that when i insert the coin the machine will be activated then active circuit will give me signal on the serial port..

means that if i m using 555 timer ic then it will give me analog signal but i have to convert analog to digital ( but how? i dont know plz tell me) then we get digital signal.. then how can i interface with serial port i dont know...
plz reply me ...