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.