Follow along with Weekend Projects as we build the Infrared String Bass, a 4-string optical guitar. Based on an older build, this project has been updated, replacing the LM741 with the LM386, which sounds great and has the added benefit of only requiring a 9V battery. The circuit is divided into three parts: the main amplifier circuit, and the emitter and detector diode circuits.

Once the circuits are wired up, any interruptions of light between the infrared emitter and detector diodes will generate a corresponding audio signal. In this case, the pluck of a string will convert light into sound!

We start by making a breadboard version of the basic audio circuit. We then multiply this circuit to accommodate four inputs, or strings. Interestingly, the color and material used for the strings produces slightly different sounds. Feel free to experiment with this! Also, feel free to experiment with the look and feel of the guitar. Since the actual body and shape of the guitar don’t effect the output like an acoustic guitar, you can mount this circuit onto whatever chassis you want. Build frets for your guitar, make an upright bass or slide guitar, and design a custom case to put all your hardware in!

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