Ah...I'm sorry I omitted that. There ARE two outputs from the photosensor pad, but I'm planning on aligning the laser so that one axis of the pad is in the plane of the laser beam and reflected beam. There will only be one degree of freedom for the object that the piezo tube is mounted to. Therefore, as that object oscillates, and the piezo along with it, the beam will "walk" back and forth on one axis of the pad, but the other coordinate will be changing. I'll draw a picture...
All right, well, I took a couple of minutes to do a crappy diagram in paint. Assume that the laser is coming in from left to right...the green thing at the bottom is a piezo tube, the laser is reflecting off of a mirror at the tip of the tube, and the reflection is hitting the detector (that little green line near the upper right hand corner), and we're imaging that it's "walking" along one of the axes of the detector. The difference in current from the right and left hemispheres of the detector is converted to voltage, from - to +3VDC. That's getting picked up and sent to the FPGA. In the case of the piezo tube, I just want to create a waveform that will try to cancel the movement of the reflective mirror and send it back to the piezo tube...which no one can find the datasheet for. So in order to keep from destroying the piezo tube with my tests, I decided to try and get the damn thing right with a speaker first. Maybe not such a great idea, since the equations of motion are not at all similar, and response won't be anything alike. But I figure, if I can write the thing and get it working for the speaker, then won't I be able to get it to work for the piezo as well by simply changing input parameters, relative gain, that sort of thing?
Well, I'll shut up now. If it still needs more clarification, please let me know...thanks a lot!
Ben
