Has anyone done any analog quadrature angular encoder work? The LabVIEW examples appear to only reference TTL type square wave counters to handle the encoders. The device I'm going to be working with is a Heidenhain Encoder RCN 729, with two sine wave outputs. I'm guessing I'd use the analog-in function on my board to sample the voltages, and an arctan function to get an incremental position, but I'm really at a loss to determine phase lead or lag if I'm only grabbing two points at a time. (Grabbing a bunch is not an option nor is post processing, the data will be used for a shut down if a certain value is exceeded).
I think you are on the right track. The analog input is certainly the way to get the current encoder values.
If the encoder produces more than one cycle or the direction of motion is unknown you cannot detemine a unique position from a single reading. (Digital encoders also cannot). You need at least two sequential data points. Use a shift register to store the previous data and compare that to the current data.