Laser Microphone

Random Thoughts

• bandpass filters to block out all but voice range.
  • Possibly adjustable in case someone's voice is deeper/higher
  • The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz
• http://www.youtube.com/watch?v=RR5tPfYWnls
  • This guy actually build an IR transmitter/receiver but it is still modulated light. He uses a carrier frequency to get rid of background noise caused by ambient light. This sounds like a fantastic idea.

Notch Filter

• http://www.members.shaw.ca/roma/nine.html
  • Has schematics specifically for 60hz hum
  • Might also be an amplifier
  • UPDATE 6/28/10
    • Haven't been able to get this circuit working yet. However, I built this other circuit (Page 41 of the link) with Todd and it worked perfectly. According to the graph on page 42, it might notch out higher frequencies too that I actually don't want to notch out. Will have to test for this by experimenting with the laser mic. The circuit on page 42 has a better looking graph so I might be able to try that circuit too if the other one filters too much.
    • http://books.google.com/books?id=-sE7JVywygQC&pg=PA41&lpg=PA41&dq=forrest+mims+60hz+hum+filter&source=bl&ots=pj3Lsh4Nq7&sig=eYwDeNs09xLpLoYo4r7fh_UpVtw&hl=en&ei=xNAoTLL2GcX_lgfDt8mECA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBYQ6AEwAA#v=onepage&q&f=false

Audio Amplifier

• http://www.techlib.com/electronics/audioamps.html#LM386
  • Has several different schematics for amplifiers.