I was thinking today of making a program for the arduino where I could input variables from my PC and run them through the program and send back the results as a pulse width or other results.
What is the PC going to do with a pulse width? What do you mean by a pulse width? Pulse width is generally a measure of how long an incoming pulse was HIGH, or the time between pulse HIGH to LOW to HIGH again.
I know this would have to be done through the serial interface, right?
Communication between the PC and the Arduino is via the serial port, yes.
I have already input variables through a keypad, etc. so I am guessing its just a matter of getting the pc to speak the correct language I need to the arduino.
I was thinking of using hyperterminal - is this the right track?
No need to guess. But, it was a reasonable conclusion to leap to. Hyperterminal is how YOU, not the PC, communicate with the serial port.
Anyone know where i should start, or how i could get the computer to input even one variable to the arduino?
The computer won't be inputting variables to the Arduino. It will be sending values to the Arduino. Big difference. The playground has a section on communicating with the Arduino, using lots of different programming languages. Personally, I think C# makes the process the easiest. YMMV.
Would it be better to use a ethernet shield or just stick with serial?
Get the communications part working using serial, first. Then, if you want, you can replace the application on the PC with a web interface, and have the Arduino with ethernet shield serve up/respond to a web page.
Is it going to be a handshake type of operation?
That's up to you.
There are some tutorials on serial comm with a PC, but I havent seen one yet where you input the variable from your PC. And most of the tutorials are a bit vague.
Tutorials are guides - not hand-holding.
I am wondering if this is even possible, and if i am getting over my head before I get started?
Yes it is, and that depends on your programming skills, understanding of communications between processes/computers, and commitment. I'd have it done in a couple of hours. You might, too, or you might take two weeks. We're here to help.
Even if you tell me im stupid for trying to do this.....<VBG>
Stupid would be throwing up your hands and not even starting.