Implementation 1.1 2007/12/19 01:33:44.788 US/Central 2007/12/19 16:57:29.301 US/Central Naren Anand nanand@rice.edu Naren Anand nanand@rice.edu Implement Laser Microphone A descrption of our Laser Microphone implementation. The hardware implementation of the Laser Microphone is relatively simple and can be done at a minimal cost.

Laser/Photodetector: The laser we used was a simple presentation laser pointer that outputted a red beam at approximately a 650nm wavelength. To receive the signal, we used a low cost photodetector (TSL12s), which is simply a photodiode and a trans-impedance amplifier combined together in a single package. The peak of the photodetector’s spectral response characteristics coincide with the output wavelength of the laser pointer.

Detection Unit: The laser capture setup was a cardboard tube with a small hole in one end for a photodetector in order to obstruct as much ambient light as possible. A power supply was used to create the 5 volt supply voltage for the photodetector and a spliced 1/8” phono jack connecter was connected to the outputted signal.

DAC: The Digital to Analog converter that we use to digitize the signal for further software processing is the mic-in jack on a laptop. Using this 22.05 kHz DAC, we are able to cheaply and properly sample the 3.6 kHz speech signal while following the Nyquist criterion and thus avoid any aliasing effects.