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The problem
Tuning a guitar by ear is a skill most beginners don't have, and ordinary clip-on tuners still leave the player to turn the peg — slow, fiddly, and hard on strings when done wrong. Digital tuners read pitch well but never close the loop mechanically: they display that a string is flat and leave the correction to your fingers. This project closes that loop. A MAX4466 electret microphone module captures the plucked string; an Arduino Nano samples the signal and runs a 256-point FFT (arduinoFFT library) to find the dominant frequency; firmware maps it to the nearest note of standard tuning and computes cents deviation; a 0.96-inch OLED shows the note name and the sharp/flat reading. When the string is outside the tolerance band, an SG90 servo fitted with a 3D-printed peg winder turns the tuning peg, waits for the string to settle, and re-measures until the reading lands within ±5 cents (design target). The result is a hands-free tuner that demonstrates real-time DSP, sensor conditioning and closed-loop control on a microcontroller budget.
Plucks the string so the microphone captures a clean note for each measurement pass.
Follow the working sequence
How it works
- The MAX4466 electret microphone module captures the plucked string; its adjustable gain is set so the loudest pluck stays within the Arduino Nano's 0–5 V ADC range without clipping.
- Firmware samples the ADC at approximately 9.6 kHz into a 256-sample buffer, applies a Hamming window, and runs the arduinoFFT forward transform to get the magnitude spectrum.
- The dominant spectral peak is found and refined with parabolic interpolation across neighboring bins, pushing resolution finer than the ~37.5 Hz bin spacing toward sub-Hz accuracy (design target).
- The refined frequency is matched to the nearest of the six standard open-string targets (E2 82.41, A2 110.00, D3 146.83, G3 196.00, B3 246.94, E4 329.63 Hz); cents deviation is computed and shown on the OLED with a sharp/flat arrow.
- If the deviation is within ±5 cents (design target), the display shows TUNED and the loop rests; otherwise the firmware computes the correction direction and magnitude.
- The SG90 servo rotates the 3D-printed peg winder — clockwise to sharpen, counter-clockwise to flatten — then pauses approximately one second for the string pitch to settle.
- The system re-samples and repeats steps 2–6 in a closed loop until the reading lands inside the tolerance band, with a servo-travel guard that stops the run before a peg can be forced.
Tech stack:
- Arduino Nano (ATmega328P, 16 MHz)
- MAX4466 electret microphone module
- arduinoFFT library with Hamming window
- SG90 micro servo motor
- 0.96-inch OLED display (SSD1306)
- 3D-printed peg winder attachment
- Arduino IDE (C/C++ firmware)
- Breadboard and jumper wiring
| Parameter | Value |
|---|---|
| FFT size | 256 points, arduinoFFT library (design) |
| Sampling rate | Approximately 9.6 kHz on ATmega328P ADC (design) |
| FFT bin spacing | Approximately 37.5 Hz at 256 points / 9.6 kHz; parabolic interpolation toward sub-Hz (design target) |
| Note targets | E2 82.41, A2 110.00, D3 146.83, G3 196.00, B3 246.94, E4 329.63 Hz (standard tuning, defined values) |
| Tuning tolerance | Within ±5 cents (design target, closed-loop) |
| Servo | SG90, approximately 1.8 kg·cm at 4.8 V (datasheet value) |
| Display | 0.96-inch OLED, SSD1306 — note name, cents, sharp/flat arrow, TUNED state |
| Microphone | MAX4466 electret module with adjustable gain |
| Correction loop | Sample → interpolate → correct → settle ~1 s → re-check (expected) |
| Power | 5 V USB or 5 V battery pack (design) |
Project features
- [FFT pitch detection] The Nano samples the microphone at approximately 9.6 kHz and runs a 256-point FFT with a Hamming window; parabolic interpolation between bins refines the peak toward sub-Hz accuracy (design target), making low E2=82.41 Hz detectable despite the coarse ~37.5 Hz bin spacing.
- [Chromatic note mapping] The detected frequency is compared against the six standard open-string targets (E2, A2, D3, G3, B3, E4); firmware picks the nearest note and computes cents deviation as 1200·log2(f/f_target).
- [Live cents display] The 0.96-inch OLED shows the note name, the cents reading (e.g. E2 +3c) and a sharp/flat direction arrow, updating after every measurement pass.
- [Closed-loop servo correction] When the reading is outside the ±5-cent band (design target), the SG90 servo turns the peg winder in the needed direction, pauses for string settling, and re-measures until the string lands inside tolerance, then shows TUNED.
- [3D-printed peg winder] A custom gripper attachment on the servo horn physically engages the tuning peg button, so the correction is genuinely mechanical rather than just an on-screen suggestion.
- [Target-string selection] A push-button steps through the six strings (or an auto mode), so the firmware knows which target frequency to aim for; an over-rotation guard caps servo travel to protect the peg.
- [FFT spectrum over serial] The raw spectrum can be streamed over USB to the Arduino serial plotter, giving a visible waveform-to-spectrum path for the report and the viva.
- [Quiet-room tuning workflow] A documented procedure: pluck, read, correct, re-check — repeatable by the student and measurable against a reference tuner app for the report's comparison table.
What is included
- Working prototype: Arduino Nano, MAX4466 mic module, OLED, SG90 servo with 3D-printed peg winder, wiring on breadboard
- Complete Arduino firmware: sampling, FFT, note mapping, cents math, servo control loop, OLED UI
- Wiring diagram and component connection list
- 3D-printed peg winder design file (STL) with fitting notes
- Quiet-room tuning procedure plus a reference-tuner comparison table for the report
- Project report PDF (DSP background, FFT method, methodology, results)
- PPT presentation for final review
- Viva Q&A preparation document (FFT, sampling, cents math, closed-loop control)
Limitations & prerequisites
- 256-point FFT gives ~37.5 Hz bins — coarse at E2 (82.41 Hz); sub-Hz accuracy is a design target via interpolation, not a lab-measured claim.
- Noisy rooms degrade pitch detection; the documented workflow assumes a quiet room, not a stage or classroom full of people.
- The SG90 delivers approximately 1.8 kg·cm (datasheet); stiff or seized pegs may not turn — the servo-travel guard prevents forcing a peg to damage.
- A 16 MHz Nano running FFT plus ADC plus servo is a stretch; each correction pass takes roughly 200–300 ms (expected), so tuning one string takes several seconds.
- Ships configured for standard tuning open strings; alternate tunings need the target table edited in firmware.
- ±5 cents is a design target for the closed loop, stated honestly — the report documents whatever tolerance the buyer's own build actually achieves.
Frequently Asked Questions
How does the FFT pitch detection work on a small Arduino?
The Nano samples the electret mic at about 9.6 kHz, fills a 256-sample buffer, applies a Hamming window and runs the arduinoFFT transform. The tallest spectral peak is the plucked string's fundamental; parabolic interpolation between bins refines it finer than the ~37.5 Hz bin spacing, toward sub-Hz accuracy as a design target.
Why is ±5 cents a design target, not a measured result?
Because accuracy depends on the student's own build: mic gain setting, room noise, string quality and servo backlash all move the number. The firmware aims for ±5 cents and reports its own reading; the report compares that reading against a phone reference tuner so the achieved figure is honest.
Can a small SG90 servo really turn a guitar tuning peg?
On a normal, free-moving peg, yes — the 3D-printed winder grips the peg button and the ~1.8 kg·cm (datasheet) servo has enough torque. Seized or corroded pegs can stall it, which is why the firmware has a servo-travel guard that stops before anything is forced.
Will it work in a noisy room?
Not reliably — the mic picks up whatever is loudest, so background music or chatter corrupts the spectrum. The project is documented and demonstrated for a quiet room; making it stage-robust would need a pickup or contact sensor, which is listed as future scope.
Is this project suitable for a final-year project?
Yes — for Electronics, E&TC and Instrumentation programs. It combines analog sensing, real-time DSP on a microcontroller, mechanical actuation and closed-loop control, with honest, measurable results a student can defend.
Components & software requirements
- Arduino Nano (ATmega328P, 16 MHz)
- MAX4466 electret microphone module
- arduinoFFT library with Hamming window
- SG90 micro servo motor
- 0.96-inch OLED display (SSD1306)
- 3D-printed peg winder attachment
- Arduino IDE (C/C++ firmware)
- Breadboard and jumper wiring
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
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