assignment: As a group was are to design and implement a universal fab class instrument. For my part I will be designing a continutity indicator that will emit a tone when there is continuity in a circuit. details: This ended up taking nearly three weeks to complete. I first built the speaker circuit. Assembly and programming of the pwm circuit was slightly more difficult than I anticipated. The first few iterations of the circuit resulted in burnt out speakers. It wasn't clear why this was happening. Someone suggested that the voltage regulator I was using wasn't appropriate for a circuit powered by a 9V battery. This didn't make too much sense but after replacing the voltage regulator the speakers stopped blowing. So there ya go. At this point I had a simple circuit that drove a speaker. next I needed to figure out how to turn the speaker on and off. I met with Jason and spoke with him a bit about microcode and he suggested that I simply change the parameter sent to OCR0B when I wanted the speaker to turn off. This seemd to do that trick. The final step was getting a continuity condition detected outside the ciruit to trigger a state change in the speaker output. I milled a modified hello3 board with the pulse triggering output moved from PIN1 to PIN0. I connected the speaker input modulating NMOSFET to PIN1. In order to trouble shoot the circuit I included a resister and zeener diode for RS-232 com as well as a couple of diodes so as to allow multiple power sources to be connected to the circuit. The .brd, .sch, .cmp and .asm files are included below. -> .sch of continuity board -> .brd of continuity board -> .cmp of continuity board -> .asm for continuity board