This would require a hardware as well as a software component. Develop an A/D module that plugs into the dock connector, and software to read the A/D module output and display the data on-screen. Presto! You have a pocket digital oscilloscope, DVM, frequency counter, etc. with touch-screen control! And it plays music, connects to the internet, e-mail results, etc. Alternatively, use a Wi-Fi connection to a wireless data-acq module. Actually, this might be better, as you could connect the hardware interface part to an inaccessible point inside a cabinet or another room, then log the results remotely. Or from multiple data-acq modules. Or the data-acq module logs measurements for a period of time, then you come back later with your iPod Touch and download the results. And this is better because there's no need to deal with the dock connector. Heck, forget the first part altogether. Do it WI-Fi. There's probably already Wi-Fi data loggers already out there.