A year ago I started work on a year-long project to make a wireless electro ocular-based eye tracking system. After a very long year, and an especially long winter semester finishing the project, I can finally say it is done. I finally finished the main sensor circuit, interfaced it all with the atmel atmega8 microcontroller, finished the desktop software to display information input from the microcontroller(with a lot of help from Kevin), designed the PCB for the project, had it manufactured, and hand soldered the final boards which were 99% surface mount. Unfortunately, there was a problem with the microcontroller losing its device ID and not programming correctly(but the sensor-circuit worked good on the pcb), so I had to demo the circuit on the proto-board….oh well. The project was a definitely a learning experience, and I learned a whole lot from it…but I’m very glad it is over.
The semester has progressed, and so has my senior project. I’ve been through three different types of op amps for the filter/amplifier stages, and finally landed on LM358’s. I’ve finally put the microcontroller on the proto-board(an atmega8), and have the whole project running off of a single 9V battery.
Though I’ve been kind of stuck doing the sensor circuit, I’ve really learned a lot of analog design. When I first started making the amplifier, it was hard to even get the input 1mV signal on the scope. After that it was hard to make and amplifier, which was followed by weeks of filter design and testing. Once I got the filters working right I found I was picking up a DC offset at the input, and since the gain of the circuit is in the thousands, I was getting a fairly large offset at the output. To fix this, I sat down and added an automatic offset compensator(an integrator and adder) to the circuit…and even though all of this was a pain the butt to do, I’m glad I’ve gone through it. Doing all this work has made me so much more confident with circuit design.
A long time coming, I finally sat down in the lab the last few weeks and hammered out the main sensor circuit for our senior project. After experimenting with many filter circuits, amplifiers, and even wiring schemes, I finally got a circuit to amplify the signal generated by the eye to a usable voltage level(around 3000 gain, ~2V). Among the pictures in the gallery, you’ll see the seemingly simple circuit, Eric hooked up to it(he survived), and the oscilloscope output. The output represents the derivative of the eye movement, in that particular case, Eric is moving his eye left to right every second or so.