Guitar Tuning Project

Project Goal

      Achieve guitar tuning function. By manually plucking a guitar string, the system will determine whether the frequency is higher or lower than the set frequency. 
      Based on the results, the system will tune the string's vibration frequency to the set frequency with a small error range (0.5Hz?).

System Overview

   The whole system is shown in Figure 1. First the microphone and preamplifier convert the guitar sound wave into a voltage wave and amplify it into AC voltage signal. This AC 
   voltage signal goes into 2 directions. 1 direction goes into a unit gain voltage buffer and then converted into a DC signal by rectifying and low-pass filtering. This DC signal 
   provides the amplitude of the sound wave to the PIC. The 2nd direction goes into a Band-Pass filter. Because the AC voltage signal from the preamplifier contains a lot of 
   environmental noise as well as harmonic waves. The band-pass filter can only let a narrow band pass with the centering frequency set by a programmable waveform generator controlled 
   by PIC (using ?). After the band-pass filter, the signal is a fairly clean sine wave signal. This signal is half-wave rectified and amplified. Later it goes into the voltage 
   comparator and becomes a square wave. This square wave is connected to the I/O pin of the PIC and the sound frequency is calculated by the PIC based upon this signal.

   With the calculated frequency of the current sound wave of the string, PIC compares it to the accurate frequency of the string stored in the program and generates corresponding
   control signals to control 6 DC motors using H bridges to tune the guitar string.