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