First, let me introduce the situation: I'm an undergraduate physics major taking a course in Experimental Physics. In the lab I am investigating the motion of natural underdampened oscillators. The oscillators under investigation are nothing more than various pieces of metal suspended between two springs in various orientations. The motion will be both free and forced. An Idea I need a way to measure and capture the motion so that I can analyze it. I have the idea of attaching a gradient film to the edge of the oscillating object. Then using a laser diode and a photo transistor I can turn the position of the object into an electrical signal. (I am only interested in a single axis of motion at this time). The idea here is that this type of sensor will not affect the motion of the oscillator because it does not physically touch it. The Problem I need a way to capture (or record) the electrical signal from the photo transistor so that I can analyze it outside of the lab. I would prefer to capture the electrical analog signal into a computer where I can easily analyze the data. The raw signal is analog and computers are digital so this is the problem. Constraints I need to do this cheaply. By cheaply I'm talking in the neighborhood of $10 to $25. Criteria The signal can be taken into the computer via the serial or parallel port. Once the signal has been digitized I can write software on the computer to capture and analyze it. The main goal of this design is to simply digitize the analog signal into a digital signal that the computer can read. The analog signal from the sensor can be chosen to be anywhere from a few milivolts to 12 VDC maximum So my real question here is this: Does anyone know of a quick and cheap way to digitize an analog signal that can be read by a serial or parallel port on an IBM type PC? Alternative Solutions As alternative interface solutions I also have the following equipment available to work with: An Xess XS-95 CPDL board - complete with a parallel PC interface An Xess XS-40 FPGA board - complete with a parallel PC interface A single board 68HC11 microcontroller called a BotBoard - complete with a serial PC interface A single board 8051 microcontroller from New Micros - complete with a serial PC interface If anyone can offer suggestions on how I can use any of these devices to solve my interface problem (or has an idea for a single chip design) I would appreciate it very much. I don't have the time to sit down and design a CPLD circuit right now but I could download a prewritten bitcode. I also don't have time to write assembly code for either microcontroller board since I am very rusty at assembly language programming. Perhaps this stuff has already been done elsewhere? Thanks in advance for any help or suggestions. And my apologies if this post is inappropriate for this topic. James P.S. Does anyone know where I can find a supplier of optical gradient film for this project?