Question

e) In order to test the functionality of a piezo sensor, we simply connect a LED with a resistance to the piezoelectric sensor. a. (5 pts) Could the LED work if we put pressure to the sensor? b. (10 pts) what is the element that we have to add ( not a rectifier circuit or capacitor )to make sure that the LED will provide light ? why , justify ? can we use aurduino for this task.

Answer 1

A sensor which works on the principle of piezoelectricity is known as a piezoelectric sensor. Where piezoelectricity is a phenomenon where electricity is generated if mechanical stress is applied to a material. The commonly measured physical quantities by a piezoelectric sensor are Acceleration and Pressure.In the pressure sensor, a thin membrane is placed on a massive base to transfer the applied force to the piezoelectric element. Upon application of pressure on this thin membrane, the piezoelectric material gets loaded and starts generating electrical voltages. The produced voltage is proportional to the amount of pressure applied.In accelerometers, seismic mass is attached to the crystal element to transfer the applied force to piezoelectric materials. When motion is applied, seismic mass load’s the piezoelectric material according to Newton’s second law of motion. The piezoelectric material generates charge used for calibration of motion.An acceleration compensation element is used along with a pressure sensor as these sensors can pick up unwanted vibrations and show false readings.

A piezoelectric sensor internal circuit is given below. The resistance Ri is the internal resistance or insulator resistance. The inductance is due to the inertia of the sensor. The capacitance Ce is inversely proportional to the elasticity of the sensor material. For the proper response of the sensor, the load and leakage resistance must be large enough so that low frequencies are preserved. A sensor can be called a pressure transducer in an electrical signal. Sensors are also known as primary transducers.

Piezoelectric sensor using Arduino

let’s look at a simple application of this sensor using Arduino. Here we are trying to toggle an LED when the pressure sensor detects enough force.

Take hardware such as Arduino board,Piezoelectric pressure sensor,LED,1 MΩ resistor.

Here the positive lead of the sensor indicated with red wire is connected to the A0 analog pin of the Arduino board whereas the negative lead indicated with black wire is connected to ground.A 1 MΩ resistor is connected in parallel to the piezo element to limit the voltage and current produced by the piezoelectric element and to protect the analog input from unwanted vibrations.The LED anode is connected to the digital pin D13 of the Arduino and cathode is connected to the ground.

A threshold value of 100 is set to the circuit so that the sensor is not activated for vibrations less than the threshold. By this, we can eliminate unwanted small vibrations. When the output voltage generated by sensor element is greater than the threshold value the LED changes its state i.e. if it is in the HIGH state it goes to LOW. If the value is lower than the threshold LED doesn’t change its state and remains in its previous state.