4.2 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.