Piezo Electric Sensor 27mm

Specifications

• Base Diameter: 27mm
• Resonant Frequency: 4.6 ± 0.5 KHz
• Resonant Impedance: 300 Ohms max
• Capacitance: 20.0 ± 30% nF
• Operating Voltage (Buzzer Mode): 1V to 30V p-p
• Output Voltage (Sensor Mode): Can generate spikes up to 90V+ on hard impacts! (Requires MCU protection)
• Drive Type: External Drive (Requires AC/PWM signal to make sound)
• Material: Brass/Copper base plate with piezoelectric ceramic center.

Applications

• Electronic Drum Triggers: The standard size for highly responsive DIY MIDI controllers and drum pads.
• Acoustic Instrument Pickups: Excellent for amplifying acoustic guitars, violins, and cigar box guitars.
• Security & Knock Detection: Build a secret "knock code" door lock or glass-break alarm.
• Smart Targets: Detect hits for Airsoft, Nerf, or laser tag target systems.
• Tactile Feedback: Use it in reverse with a PWM signal to act as a low-profile beeper.

Unlock New Capabilities

• Past Projects: If you've mastered basic push-button inputs and digital switches...
• Feature Upgrade: This sensor unlocks Analog Impact Sensing. You can measure how hard something is hit (velocity/force), not just if it was hit.
• Effort/Requirements: Intermediate. You cannot just plug this in! It requires a basic understanding of voltage dividers and a minimum hardware addition of a 1M Ohm resistor to protect your board.

Virtual Technician & Wiring Guide

• ⚠️ CRITICAL VOLTAGE WARNING: Piezo elements generate high voltage spikes when struck hard. Never connect this directly to a 3.3V (ESP32/RP2040) or 5V (Arduino) microcontroller without protection. You will fry your ADC pin!
  Wiring (Standard Arduino Knock Sensor):
• Piezo Red Wire: Connect to Analog Pin A0.
• Piezo Black Wire: Connect to GND.
• 1M Ohm Resistor: Connect one leg to A0 and the other leg to GND (in parallel with the piezo). This drains residual capacitance and protects the board. For high-impact setups, add a 5.1V Zener Diode in parallel to clamp voltage spikes.

Package Including:

• 1 X Piezo Electric Sensor 27mm

Frequently Asked Questions (FAQ)

• Can I connect this piezo directly to an Arduino?
  No, you must use a 1M Ohm resistor in parallel to protect the analog pin from high voltage spikes and bleed off the charge.
• What happens if I hit the piezo too hard?
  It can generate transient voltages exceeding 50V, which will permanently destroy your microcontroller's ADC if left unprotected.
• How do I protect my Raspberry Pi from this sensor?
  The Raspberry Pi has no native analog pins. You must use an external ADC (like the MCP3008) alongside a 3.3V Zener diode for voltage clamping.
• Does this work as a buzzer to make sound?
  Yes, but it requires an AC or PWM square-wave signal from your code. It is an active transducer, not a continuous DC buzzer.
• Can I use this for an electronic drum kit?
  Absolutely, the 27mm size provides the ideal surface area and sensitivity for responsive MIDI drum triggers.
• Why is my knock sensor reading constantly high?
  You likely forgot to add the 1M Ohm parallel pulldown resistor to drain the internal capacitance.
• Which wire is positive and negative?
  The inner white/silver ceramic circle (usually the red wire) is positive, and the outer brass plate (usually the black wire) is ground.
• Can I cut or trim the 27mm brass plate?
  It is highly discouraged; cutting the brass will likely shatter or micro-fracture the fragile ceramic element on top.
• What is the resonant frequency of this disc?
  It is tuned to approximately 4.6 kHz, which is the frequency at which it is loudest when driven as a speaker.
• Is this component waterproof?
  No, the bare ceramic and brass elements will easily corrode if exposed to moisture or extreme humidity.
• How do I attach it to a surface for sensing?
  Double-sided foam tape, hot glue, or cyanoacrylate (superglue) work best for transferring acoustic vibrations into the plate.
• Why is the sound so quiet when I use it as a buzzer?
  Bare piezo discs need an acoustic resonance chamber (a plastic housing or 3D printed shell) to amplify the sound waves effectively.
• Can I use this as an acoustic guitar pickup?
  Yes, many luthiers glue these directly to the soundboard and wire them to a standard 1/4" audio jack.
• What is the difference between 20mm and 27mm piezos?
  27mm discs produce slightly lower frequencies and are generally more sensitive to micro-vibrations due to their larger surface area.
• Can this measure continuous pressure or weight?
  No, piezos only generate a voltage spike during a change in pressure (dynamic force), not static weight.