Initial reported by Erin Kim, 2 November, 2005

Introduction

I chose the LDTM-028K, a laminated Piezo sensor from measurement specialties. It is different from resistive sensors such as the bend sensor and the photocell sensor because they generate electricity in response to applied stresses. When the piezo film is bent from the mechanical neutral axis, a very high strain within the piezo polymer is created and generates a high voltage. This voltage is created only as the sensor is deformed. The sensor produces positive voltages when they're deformed in one direction, and negative voltages when deformed in the other.

Simple Concept Diagram

image from www.makingthings.com

Structure

  • DT Series Elements

The DT series sensor are the simplest and standard form piezo film sensors.The capacitance is proportional to the area and inversely proportional to the thickness of the element.

  • LDT Series Elements with Lead Attachment and Lamination

The 'L' in LDT stands for 'laminated' sensor. Typically, a 0.005" (125㎛)polyester layer is laminated to a 28 ㎛ or 52 ㎛ piezo film element. When used in a 'bending' mode, laminated film elements develop much higher voltage output when flexed than non-laminated (i.e., DT series) elements.

Applications

TYPICAL APPLICATIONS FOR PIEZO FILM SENSORS

  • Accelerometer
    • Car Alarm
    • Biomedical Monitoring
  • Vibration/Motion Film Sensor
DT series
  • Dynamic Strain Gages
  • Musical Instrument Triggers
LDT series
  • Antitheft Alarm
Vending
  • Dispensing Verification
  • Coin Drop Counters
  • Antitamper
  • Penetration Panels
Appliance Monitering
  • Microwave - Sound Pickup
  • Washer Imbalance
  • Water Flow Sensor
  • Ultrasound
    • Shockwave Sensors
    • Air-Ranging Proximity
    • Robotic Tactile Sensors
  • Audio/Acoustic
    • Microphones
    • Speakers
  • Traffic Sensors
    • Vehicle Classification
    • Airport Taxiway

Here are more examples using Piezo element.

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If it ain't got that swing...__student project

Good Application notes from MSI site.

Electrical Characteristics

Datasheets

Technical Manual

  • Maximum Operating Voltage
DC : 280 V
AC : 840 V
  • Maximum Applied Force
6-9 kgF (voltage output of 830 to 1275 V)
Description Part No. Capacitance
ModelPart NumberCapacitance
LDT0-028K/L0-1002794-1500 pF
DT1-028K/L1-1002908-01.3 nF
DT1-052K/L2-1002908-0650 pF
DT2-028K/L1-1003744-02.6 nF
DT4-028K/L1-1002150-09 nF

I also recommend referencing Piezo System,INC website for more information. Specifically, Technical/FAQ's section got more details aboutPiezoelectricity and Nice lists of recommended reading.

Microcontroller Connection

Schematic

Ampilification -Op amp

Op amp(Operational Amplifier) take a very small voltage signal and amplify it to a range that's readable.

  • Resister
You can change the amplification factor of the op amp by changing the two resistors attached to the negative input pin.
  • Diode
Zener diode allows electrical energy to pass up to a certain voltage and cuts the rest off.

For more technical introduction, see Practical Electronics for Inventors by Paul Scherz & The IC OpAmp Cookbook by Walter C.Jung

Application Notes

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