9th Grade Honors Physics Project

As my 9th grade, Honors Physics, end of year project, I built a set of devices with simple and cheap circuits to send and receive audio signals over distances via a laser beam.

Parts

• Altoids Metal Tins
• Generic Red Laser
• Infared Photo Transistor
• LM386-N Audio Amplifier Chip
• Small Speaker
• Prototyping Boards
• 9 Volt batteries
• Variety of through hole components, capacitors, switches, potentiometer.

Details

I got the idea for this project from a DIY video doing a similar project. In order to transmit audio over a laser beam, you need to take the music input from one side and amplify it to power the laser. As the music plays, the amplitude (or brightness) of the laser is varied with the music / audio. On the other side, a similar circuit works to reduce the voltage down to a level to power the speaker to replicate your music. This amplification and reduction in power needs to be done all while preserving the integrity of the audio track. In order to do this we chose the LM386-N an IC chip made specifically for this purpose. I soldered the components together on a prototyping board and placed the two circuits into individual metal tins, with holes for the laser and sensor. To demo, I played music into the microphone on one side, and heard the audio come out of the speaker on the other side, with only a laser beam in between.