FFT Math & Stepper Actuators: Automatic Guitar Tuner

Standard audio processors tell you if the music is loud. The Automatic Guitar Tuner requires the math to tell you what the exact Frequency is (Hertz) explicitly. By hijacking the massive mathematical capabilities of the Uno's Analog-to-Digital Converter, passing the string vibrations through complex Operational Amplifiers (Op-Amps), and linking the exact pitch discrepancy to a massive Stepper motor clamped physically onto the guitar peg, the Arduino mechanically tunes the physical metal strings to absolute perfection!

The LM386 Op-Amp Zero-Crossing Trap

You absolutely cannot read an electric guitar directly into an Arduino Analog Pin. The signal is incredibly weak (10mV) and floats perfectly below Ground (AC Voltage - +10mV to -10mV)!

1. The Uno A0 pin reads 0V to 5V. If a negative voltage hits it, the pin physically ignores it!
2. You MUST run the guitar through an LM386 Operational Amplifier (Op-Amp)!
3. The schematic chemically "Biases" the audio signal up to exactly 2.5V. Now the guitar wave wildly swings between 2.0V and 3.0V.
4. The Software Read Engine: The algorithm searches for Zero-Crossings. Exactly how many times a second does the amplified waveform slice across the 2.5V baseline?
5. Low E String = 82 Hz. The Uno calculates If (Hertz < 82.4): The string is FLAT!

Actuating the Gearbox (Geared Stepper)

If the note is flat, the Uno must violently actuate physical robotics to physically tighten the metal guitar string.

• You CANNOT use a standard DC Motor; it will spin out of control and snap the string!
• You MUST use a 28BYJ-48 or NEMA 17 Stepper Motor.

if (currentHertz < 82.0) { // Extremely Flat!
  // Tighten string massively!
  tuningStepper.step(100); // 100 perfectly controlled steps clockwise!
} else if (currentHertz >= 82.0 && currentHertz < 82.3) { 
  // Very close! Micro-adjust!
  tuningStepper.step(2); // Tick just 2 steps!
} else {
  Serial.println("IN TUNE!"); // Halt all machinery!
}

Pitch Mathematics Base Hardware

• Arduino Uno/Nano (Standard execution speeds are perfectly sufficient, though teensy boards are better for raw FFT library deployments).
• LM386 Audio Amplifier Chip + physical bias resistors and coupling capacitors (A complex breadboard array is absolutely mandatory or the sound physics will fail instantly!).
• Standard Electric Guitar 1/4-inch Mono Jack Cable Breakout.
• Geared Stepper Motor (Coupled exactly to the guitar tuning pegs using a custom 3D-printed hex adapter!).