Capacitive Touch Piano using TTP223 Sensor Modules

Capacitive touch sensing is everywhere — phone screens, elevator panels, appliance controls — yet students usually meet it only as a paragraph about changing capacitance. A touch piano turns the concept into something you can hear: each key is a TTP223 single-channel capacitive touch module whose output flips the moment a finger approaches its pad, with no moving parts and no mechanical bounce to debounce. The Arduino Nano reads all eight keys, looks up the exact musical frequency for the pressed note, and generates it with hardware-timed square-wave synthesis through a small power amplifier. Per-key LEDs give visual feedback, and an octave-shift button doubles the playable range. It is a compact, genuinely playable instrument that demonstrates capacitive sensing, embedded timing and basic audio electronics in one build.

1. Each TTP223 module continuously measures the capacitance of its touch pad; a finger's approach changes it enough to flip the module's digital output high.
2. The Arduino Nano polls (or interrupts on) the eight key outputs and identifies which note was touched.
3. The firmware looks up the key's equal-temperament frequency and starts a hardware-timed square wave at that exact frequency.
4. The square wave passes through a volume control into the PAM8403-class amplifier, which drives the 8 Ω speaker.
5. The LED for the active key lights for the note's duration; releasing the key stops the tone (or sustains it in hold mode).
6. Pressing the octave-shift button adds or subtracts 12 semitones from every key's lookup, extending the range without extra keys.
7. Only one note sounds at a time — a deliberate consequence of single-timer synthesis, documented as a limitation with the polyphony extension in future scope.

Tech stack:

• 8 × TTP223 capacitive touch sensor modules
• Arduino Nano (ATmega328P)
• PAM8403-class audio amplifier + 8 Ω speaker
• Per-key LEDs with current-limiting resistors
• Octave-shift and sustain push-buttons
• Volume potentiometer
• Acrylic/wooden key panel with printed note labels
• USB 5 V / 9 V battery power

• [Eight TTP223 touch keys] One octave (C4–C5) of capacitive touch pads — no moving parts, no mechanical contacts, no debounce code needed.
• [True note frequencies] Equal-temperament frequencies from 261.63 Hz (C4) to 523.25 Hz (C5) generated by hardware-timed synthesis, not approximate guesses.
• [Per-key LED feedback] An LED above each key lights while its note sounds, useful for teaching and for visible demo feedback.
• [Octave shift button] Shifts the whole keyboard up or down one octave, doubling the playable range to C3–C6.
• [Audio power amplifier] PAM8403-class amplifier drives an 8 Ω speaker to classroom-audible levels, with a volume knob.
• [Sustain/hold mode] A toggle holds the last played note for demonstrating envelopes, or plays staccato on touch-release.
• [Labeled key panel] Acrylic/wooden panel with printed note names (C D E F G A B C) under each touch pad.
• [USB or battery power] Runs from USB 5 V or a 9 V battery through the onboard regulator.

• Assembled key panel with 8 TTP223 modules, LEDs and printed note labels
• Arduino Nano controller with amplifier and speaker, wired and tested
• Firmware source (key scanning, frequency tables, octave shift, sustain)
• TTP223 sensitivity-adjustment notes for the student's own tuning
• Wiring diagram and enclosure/panel drawings
• Project report PDF, PPT presentation and viva Q&A document

• Monophonic: only one note sounds at a time, a hard limit of single-timer square-wave synthesis on the ATmega328P — polyphony needs a different synthesis architecture (noted in future scope).
• One physical octave; the second octave comes from the shift button, not extra keys.
• Capacitive keys need a reasonably clean ground and stable supply; noisy USB chargers can cause false triggers — the kit documents sensitivity tuning.
• Square-wave tone is a buzzy piano approximation, not a sampled piano; a low-pass filter softens it but the timbre stays simple.
• Touch response and loudness figures are expected/design values; the report includes the student's own verification procedure.