Hi Guys, I'm working on a project at uni that involves building a EPIRB (Emergency Position Indicator Radio Beacon System). It needs to be in a $100 budget. I've been looking at different parts of this project and I need to build a filter (for the 800Hz frequency our receiver will output) and a sine-square wave converter to get the 800Hz filtered frequency in digital form to the micrcontroller. I'm confused at whether to build a bandpass filter for the 800Hz frequency or a high pass and low pass filter. Also I'm not sure on how to get the square wave to go to the micro. My tutor said to use a high gain op-amp. But I'm a little confused about the circuitry. Also I need to build a 9v to 5v voltage regulator but we cant use the LM7805 because of the 2v drop out voltage. Any ideas on that? I'd really appreciate some help. Thanks!