Design of a Multi-Effects Guitar Pedal Controlled Via Bluetooth App

Abstract

For decades, guitar effect pedals have been used by musicians across many genres of music to produce an unique and innovative sound. Many artists may have perhaps a dozen different pedals, each with different settings, to produce the desired effect. This can cause a clunky transition from song to song or even section to section. The main goal of this project was to streamline the process of changing effects, eliminating the time needed to adjust the various dials and switches to get the targeted sound.A simple Android app was developed using the Bluetooth Low Energy (BLE) API to interface with an RFduino microcontroller. The app was designed to be controlled intuitively, with simple buttons and slide bars to control which effects and what settings are enabled. The RFduino programs a shift register to drive a relay network using BJTs. The relays are used to bypass different circuit elements to produce different effects. The RFduino also programs a digital potentiometer to change gain values, volume, and frequency of oscillation.Currently implemented effects include distortion, overdrive and variable frequency tremolo. The design is intended to be easily extendable to other effects such as chorus, phaser, flanger, etc. Using shift registers allows essentially unlimited expansion using only three GPIO pins. Each additional effect would only require additional relays to be installed and minor software modifications.