Ok so I am trying to get the arduino to talk to a standalone instrument that can communicate via serial plug with a very basic protocol. The arduino would then turn a servo that changes what source the instrument measures and relays the information to a PC.
Essentially I need to get the arduino to let me plug the instrument into it and the arduino then plugs into a PC. Is this possible? I just need a little advice on what hardware or libraries I'm going to need to get started.
The Arduino has the chops to do what you want. It's USB port can communicate with the PC and you can use a software serial library to use two pins to talk to your instrument. First thing is to find out about the instrument's communication details. What voltage levels does it use, TTL or RS-232?, etc? Baud Rate? And you will have to know the instruments protocol for how it talks to your Arduino controller.
Lefty
If it's not easy to get your instrument to shut up and wait for your instructions (e.g., it sends "attention" messages at unpredictable times), consider using the new Arduino Mega to get extra hardware UARTs: the software serial libraries tie up the whole CPU while waiting for serial data, but the hardware UART drivers run "in the background" and will save incoming data in a buffer until you ask for it.
The serial and servo libraries are part of the standard development software download, so you shouldn't need to add any extra software to get your application running.
Ran
I've used the device in question before and communicated with it through a command line interface in winxp(I forget what it was exactly, I'm thinking telnet). It didn't send extra messages visible in that, or would they have been filtered out?
Right now I'm constructing a prototype of this device so I'm hoping to just use my current arduino. If it's not possible then I'll just have to sell another kidney and splurge on the mega... 