Simple Vibration Sensor Circuit

As its name suggests, this simple vibration sensor circuit using piezo transducer allows for the detection of vibrations to which its sensor is subjected. Unlike superficial pressure sensors whose resistance varies depending on the force they are subjected to, the transducer used here is only sensitive to variations in pressure exerted on its sensitive face.

The 27 mm piezo transducer which is used for this vibration sensor circuit is shown in the following image.

How the Circuit Works

The following figure reveals the diagram of our simple vibration sensor circuit using piezo transducer. The sensor used is a piezoelectric blade. The application of a force to this transducer causes a deformation which results in the appearance of electrical charges on the opposite faces.

This phenomenon is visible on an oscilloscope and is represented on our board by a series of impulses at the ends of resistor R1.

This voltage is then sent through capacitor C3 to the amplifier built around transistors T1 and T2. The polarization of the whole system is ensured by the voltage divider R1 and R5.

Resistance R7 is decoupled by capacitor C5, which gives transistor T1 a significant gain, while transistor T2, which is connected in a common emitter configuration, allows for a low output impedance.

Resistors R2 and R3, on the one hand, and adjustable resistor Aj1 on the other hand, constitute the feedback network.

The gain of the amplifier is expressed by the formula G = Aj1 + R3 / R2. The attentive reader will have noticed the presence of capacitor C4, which prevents any continuous feedback.

The amplifier output drives the two flip-flops contained in a 4013 package.

Flip Flop Working

Consider flip-flop A on the diagram: a positive, albeit brief, pulse on its input will cause the output Q1 to go high, which will be maintained after the pulse disappears.

The return to the reset state can only be achieved by pressing the push button BP.

This operating mode is of the bistable type. The flip-flop B works a little differently: when the Q2 output is high, the charging of capacitor C1 through resistor R10 and adjustable Aj2 begins.

As soon as the voltage on pin 10 of IC2 exceeds half the supply voltage, the Q2 output switches to the low logic level, which is the monostable mode. The output pulse has a duration of 70 to 75 ms depending on the setting of Aj2.

The unipolar inverter, labeled INV on the diagram, allows the choice of either mode of operation.

It drives the base of transistor T3, which is configured as an open-collector, allowing for very flexible use of the circuit. It is possible to connect a relay to the collector of T3.

It is also possible to drive a logic board via T3. It should not be forgotten that, in such a case, the transistor behaves like a logic inverter.

For reliable operation of the circuit, it is imperative to stay below the maximum values of T3, whose main characteristics are as follows:

VCEO = 50V, IC max. = 600mA,
P max. = 800 mW, (T° = 25°).

The power supply of the prototype is provided by a simple 78L12 regulator.

The circuit will be powered by a voltage of at least 15V (maximum 35V) which must be perfectly filtered but not necessarily stabilized.

The idle consumption is a few milliamperes.

Construction

The implementation of the printed circuit board presents no particular difficulty and all usual reproduction methods can be used.

The 4013 IC will be installed on a socket, while the piezoelectric sensor will be connected to the input terminal via two flexible wires.

The adjustable resistor Aj1 allows adjusting the sensitivity of the circuit, with the median position generally being suitable.

Applications of this Vibration Sensor Circuit

A piezo transducer vibration sensor circuit with a flip flop relay can have several applications, including:

Intruder detection: This type of circuit can be used in security systems to detect intruders. When the piezo transducer detects a vibration or shock, it triggers the flip flop relay, which can then activate an alarm or notify security personnel.

Machine monitoring: This type of circuit can be used to monitor machines and equipment. When the piezo transducer detects a vibration or shock, it triggers ON the flip flop relay. The switched ON relay can then be used to turn ON a shutdown the system to prevent further damage to the equipment.

Monitoring of structures: This kind of circuit may be used to keep tabs on the condition of buildings and bridges. The flip flop relay is activated when the piezo transducer senses a vibration or shock. The relay can then turn on a warning system to inform engineers or maintenance staff.

Seismic monitoring: This type of circuit can also be used in seismic monitoring. When the piezo transducer detects a seismic event, it triggers the flip flop relay, which can then activate a data acquisition system to record the event.