Homemade vibration sensor. Piezoelectric vibration sensor in a seismic detector. Not enough information

Diagram of a simple but sensitive vibration sensor on the op-amp LM358. The adjustment device does not require and starts working immediately. Responds to steps from a distance of several meters.

The vibration sensor circuit is shown in the figure below:

A flat piezo emitter is used as a sensor. wrist watch or similar. The wire from the central plate of the piezoelectric element is connected to the input of the op-amp. The piezoelectric element itself is fixed on the controlled surface. To enhance the sensitivity to the base of the piezoelectric element, you can attach a small spring with a weight so that the piezoelectric element bends. At rest, the voltage at the non-inverting input of U1 is a few millivolts lower than at the inverting one. Therefore, at the output U1 (vyv.1) there is a voltage close to 0 (log.0). When vibration occurs, an additional voltage appears at pin 3 of the op-amp, which, in total with the constant voltage from the divider R3-R1-R2, turns out to be higher than at pin 2. The op-amp switches, and a voltage close to the supply voltage appears at its output (log. 1 ). Thus, rectangular pulses are formed at the output of the sensor in time with the vibration. The output signal is applied to pin 2 of connector J1.

Resistor R1 selects the sensitivity of the sensor. Its value can range from 0.33 ohms to 10 ohms. The lower the resistance, the higher the sensitivity. Capacitor C1 acts as a filter, eliminating false positives from single pulses. Resistors R2 and R3 must be the same resistance from 1 to 3 kOhm. Resistors R4 and R5 must also be the same resistance from 47 to 200 kOhm.

The sensor can be powered by voltage from 4 to 12 volts. Resistor R6 limits the output current in the event of a supply voltage greater than 5 volts and a sensitive load at the output. The output of the sensor can be connected to a microcontroller or a transistor that controls, for example, a relay. An LED or a voltmeter can also be connected to the sensor output.

The sensor can be assembled on a printed circuit board, the drawing of which is shown in the figure:

The piezoelectric element will connect through the connector on the left. The wires to it must be twisted together.

The basis of the sensor is a piezoelectric element from the sound emitter ZP-2, ZP-4 or ZP-5. General form sensor (side) is shown in Fig. 1, a. Piezoelectric element 2 of one of the plates is soldered to the foil pad printed circuit board 1. To the upper plate of the piezoelectric element 2 according to the figure, a rack 4 is soldered, bent in the form of the letter L from an elastic steel wire with a diameter of 0.5 mm. View of rack 4 along arrow A is shown in fig. 1.6. The legs and saddle of the rack must be irradiated in advance.

The console 3 is bent out of the same wire and a load 5 weighing 10...15 g of lead or solder is securely fixed at one of its ends. After that, the console is soldered with one end to the board, and approximately in the middle - to the saddle of rack 4.

In order to avoid tearing off the upper plate from the piezoelectric element, before soldering the console, it is slightly bent so that, after being put in place, it creates an excessive pressing elastic force on the piezoelectric element. The dimensions of the sensor parts are not fundamental, therefore, they are not given in Fig. 1. It is necessary to solder with low-melting solder.

The sensor outputs are a foil pad, to which a piezoelectric element is soldered, and a console base soldered into the board. The board is fixed on the surface,

vibration to be controlled. When this surface mechanically vibrates, several weak pulses with a duration of 3 ... 15 ms appear at the sensor terminals.

In order to amplify these pulses and give them the shape necessary for further processing, the signal from the sensor is fed to the input of the amplifier-shaper (see diagram in Fig. 2). Operating Wuxi

Liter DA1 operates in maximum gain mode, and transistor VT1 - in switching mode. Diode VD1 increases the dead zone of the transistor with its cutoff voltage.

The op-amp, together with a diode and a transistor, form a voltage comparator, characterized by low power consumption. The threshold for the comparator is set by a trimmer resistor R2. If the amplitude of the negative half-wave of the sensor signal is less than the voltage across the resistor R2, the transistor VT1 remains closed, and the output voltage is zero.

Mechanical excitation of the sensor leads to the appearance at the output of the shaper of several rectangular pulses with a duration of 3 ... 15 ms, in amplitude suitable for their direct injection into a digital analyzer made on CMOS microcircuits. The simplest such device capable of isolating a useful signal against the background false positives, is a counter (001 in Fig. 2), periodically reset at the input R by pulses electronic clock or a special generator. Alarm - Voltage high level- will appear at the output only when the number of pulses at the input of the counter in the interval between two adjacent zeroing pulses reaches a certain number set by the switch SA1 (in Fig. 2 it is set to eight).

If you do not set a solution to the problem of eliminating false signals, then the signal from the collector of the transistor VT1 can be applied directly to the input of the alarm generating unit.

As experience shows, the sensor practically does not respond to acoustic signals propagating in air environment. Sensitive primarily to the normal component of vibrations, it also perceives quite well perturbations lying in the plane of the piezoelectric element, apparently due to the occurrence of a reaction at the points of attachment of the rack. Thus, the sensor responds to vibrations of arbitrary orientation. The current consumed by the conditioning amplifier in standby mode at a supply voltage of 9 V does not exceed -18 μA, at 5 V - 10 μA.

Source: RADIO 12/94

This article describes the device of a seismic sensor-detector, which is a sensitive electronic unit capable of detecting even a very weak level of vibration in the earth's crust.

The design of the seismic detector used piezoelectric vibration sensor which is very sensitive to vibrations and shocks. This scheme can be used to detect tremors of various objects, vibrations occurring in the earth's crust, or as an integral part of the security system.

Description of the work of a seismic detector on a piezoelectric element

As mentioned above, the main element that is sensitive to vibrations is a simple buzzer (piezoelectric element). It is quite often used in devices designed to detect vibrations and shocks, for example, in burglar alarms for bicycles. The advantage of the scheme is not only the low price, but also the easy installation of the sensor, often simply by gluing it on the surface to be monitored.

The DA1 chip is an operational amplifier of the LM741 type, designed to amplify weak signals from a piezoelectric element. The amplified signal from the output of the operational amplifier through the resistor R6 is fed to the base of the transistor VT1. As a result of this, the transistor opens and a low level signal appears at input 2 of the NE555 timer (less than 1/3 of the supply voltage).

A classic standby multivibrator is built on the NE555 timer, which is triggered by a low signal at pin 2. As a result of starting the multivibrator, a signal appears at its output (pin 3) that turns on the buzzer (with a built-in generator) and the LED lights up.

The duration of the signal is determined by the elements of the RC circuit (R8 and C2). With the indicated values ​​in the diagram, this period is approximately 3 minutes. After this time, the device returns to the initial state.

vibration detector

Such a device can detect any type of mechanical vibrations, can be used to solve various everyday problems. To achieve this sensor, we used small piezoelectric discs, which are contained in the buzzers. It will find its application in alarm systems or in security systems Service systems. The idea for this assembly was born from the frustration of some of the building's tenants, parking their car in their place, turned out to be too often in the morning with a body dented and, of course, without any - . or indications of the identity of the offender despite the fact, decided to shame the tenant of the unscrupulous dork purchasing space to perform their clumsy maneuvers at the expense of neighboring vehicles, they decided to install vibration-sensitive circuits on the board. So, over the course of several nights, they discovered that the dehorner of the unrepentant leaf was none other than the son of the tenant, a young driver, returning in the early hours of the night to the disco, a little tipsy, having lost his sense of late Has acquired the geometry of parking lots and especially probably not learned from responsibility to the detriment of others. The original anti-theft THIS vibration sensitive circuit can be used NOT only: To be notified immediately if someone hits your parked car or motorcycle, but if a tramp tries to force the door of your house. we will tell you what we used to service the detector (or sensor) to excite the vibration relay to control the pulpit: a siren or any other element that can be controlled by a relay. The small piezo disk inside the piezo buzzer is a small disk (3 and 4) for transmitting sound when applied to the acoustic frequency terminals. These small disks can also work in reverse, that is, if vibrated mechanically, can, at their terminals, collect a BF SIGNAL of 20 mV approximately. this function, Electrical Signal Receive via Vibration piezoelectric with US Capsules is used in the "pickup" (turntable heads) to control the sounds when their tip scans the groove of the disc. black We assure you in advance about that, : To get this little piezoelectric disc you will have to buy an expensive buzzer and then destroy it to extract the precious little disc: on. is it really available and only cheap? How to vibrate this small disc in THIS small vibrating disc, weld, on its face completely made of brass, hard wire, iron or brass, with a diameter of 2 mm and a length of 70 mm (3 and 4). Thereafter, insert the free end of the wire into a 3-pole terminal block, serving as a "counterweight" to transmit the vibrations detected to the piezoelectric disc. The electrical signal transmitted by this disk is taken from the side where the surface is completely white and, for this, it is necessary to weld the end of the copper wire connected to the inverting input of the operational amplifier IC 1-a through a 10 kΩ resistor R3 (1 and numbers 5). the opposite side, whose surface is made of brass, is connected to the non-inverting + IC1 connector-A and is powered by a positive 6V voltage across the resistor terminals and R1 R2. Wiring diagram we have already said, the electrical signal generated by the oscillations charged on both sides of the piezoelectric disk is applied to the input contacts of the first operational amplifier IC 1-charge amplify approximately 100 times (Figure 1). The amplified output signal from pin 7 of IC1-A is rectified by a silicon diode DS1 and a DC voltage is used to charge an electrolytic capacitor C5 located at the inverting input of the second operational amplifier IC1-B. The non-inverting input of the same opposite IC1-B is connected through a resistor R8, R6 to a trimmer to control the sensitivity cursor. Whenever the piezoelectric disc receives vibration, the DL1 LED. connected to the output pin 1 of IC1-B lamps Lighting Impulse Between this indicator, through the capacitor C6, in pin 2 of IC2 integrated circuit NE555 mounting single vibrator. each input PIN 2 pulse of IC2 is taken to pin 3 of a positive voltage, the polarizing base of the NPN transistor TR2, puts IT in a conduction state, which energizes the relays connected to its collector. : When the relay is energized, the LED DL2, connected in parallel with the relay coil, lights up. the circuit is composed of resistors R12, R16, R17, C9 electrolytic capacitors and diodes DS2 , DS3, DS4, serves to avoid that whenever the relay releases, mechanical vibrations are detected by the piezoelectric disc, exciting again. trimmer R14 connected to pins 6 and 7 is used to keep the relay energized from 2 seconds to 2 minutes. Transistor TR1, the collector connects to pin 4 of IC2 to keep reset provides the integrated circuit for about 10 seconds, every time, by us the assembly is energized. This is necessary to avoid that the detector has control over before we could leave. and doors Closing the car All Can be powered by stabilized circuit 12 V. Figure 1:. vibration detector circuit on small piezoelectric disks, the signal generated by some kind of mechanical vibration is taken and applied on two input pins of op-amp IC1-A (5 and 6 .) Figure 2: picture of ours. Vibration detector Figure 3: full copper side of a small disc, solder hard wire 2mm in diameter and 70mm in length, approx. Figure 4:. at the end of the wire a counterweight (terminal block) will be fixed. vibration sensor circuit components implementation. The small disk of the piezoelectric capsule is inserted into the slot near R3 soldering then On the "white" area of ​​the smallest disk, solder the end of the copper wire to remove the signal. Figure 5b Dimensional drawings of 1 double-sided printed circuit board with through-hole sensor plating. vibrations. Side Components Figure 5c: Dimensional drawings 1 PCB double sided with galvanized through SENSOR Vibration holes. . solder side PART LIST R1=10KW R2=10KW R3=10KW R4=1M R5=1.5KW R6=1kΩ trimmer R7=2.2KW R8=10KW R9=1M R10=1MΩ R11 = 1 kΩ R12 = 10 kW R13 = 22 kW R14 = 1 M trimmer R15 = 10 kW R16 = 47 Ω R17 = 3.9 kW R18 = 10 kW R19 = 22 kW R20 = 47 kW R21 = 47 kW R22 = 1 kΩ C1 = 100 nF polyester C2 = 10 µF electrolytic C3 = 1.5 nF polyester C4 = 10 µF electrolytic C5 = 2 2 µF electrolytic C6 = 100 nF polyester C7 = 100 µF electrolytic C8 = 10 nF polyester C9 = 100 µF electrolytic C1 0 = 100 uF electrolytic C11 = 100 nF polyester DS1 = 1N4148 diode DS2 = 1N4148 diode DS3 = 1N4148 diode DS4 = 1N4148 diode DS5 = 1N4148 diode DS6 = 1N4007 diode DL1 = LED diode DL2 = LED diode TR1 = NPN BC547 TR2 = NPN BC547 IC1 LM358 Integrated = IC2 = Integrated NE555 RELAY1 = Relay 12V 1RT Figure 6:. Photo of a Vibration SENSOR prototype AFTER soldering a small disk into a slot. circuit, we must also fix the end of the counterweight wire and for this we use a 3-pole terminal connector Figure 7: Pin outputs of two integrated circuits and LM358 NE555 if viewed from above and with the U-key left. Pinout of the BC547 transistor seen from below and the LED (long leg of the anode). , but another object will do, for example, a nut or "lead" a seal). practical implementation on PCB double sided plated through holes, it is necessary to mount all components as shown in Figure 5. We recommend starting with integrated circuit carriers IC1 and IC2 and after soldering all the pins, continue the resistors, controlling their value well. left side of the PCB, insert the R6 1 kΩ trimmer. In the center, place the trimmer R14 to 1 MΩ. Then you can start to put on and weld the diodes DS1 to DS6 by guiding their ring with a wrench, as shown in Figure 5. After these components, mount the polyester capacitors and electrolytic capacitors, observing, of course, the polarity of the latter. insert and solder two transistors TR2 and TR1 without cutting their legs, directing them flat in a good way, always shown in Figure 5. at the end, insert and solder more and two terminals adjacent to it, and then insert two chips in: their sockets with their surcharge key U point in the right direction as shown in Figure 5. LM358 (IC1) surcharge key to the right and NE555 (IC2) body mark to the left (two-marker locators face) This device can be hidden in a car or in a house near us to go planned No enclosure (but you can provide one). In addition, can be inserted directly on the LEDs from the PCB polarity: their legs to complete the vibration detector, you just have to insert into the socket provided on the PCB near R3 piezoelectric disc and solder on both sides, as shown in Figure 8. on opposite side of the disc, the face of the "white" solder a thin copper wire going to the hole near R3 (Figure 5). When using enamel wire, remember before welding it, scratch the insulating layer of enamel with a knife or sandpaper, otherwise the solder will NOT accept contact and will NOT. do We decided to insert a piezoelectric disc directly into the circuit, but it can also provide a separate circuit for one disc: you can then place this remote control sensor, for example, in the trunk of a car or in a door by fixing it with stained floors of any complexity. In order to bring the drive signal to the PCB, a small shielded cable can be used when the braid is connected to the trace to the non-inverting input of IC1-a and the core carrying the signal to the track from the input impedance R3. Setup and testing AFTER the installation is completed, it is necessary to adjust the R6 sensitivity trimmer and the trimmer delay, setting the time for the relay,. R14 you don't need any measuring instrument to do this:. a small screwdriver is enough to start, turn halfway CURSOR two and trimmers R6 R14 Complain about then put the vibration sensor on the table and supply power to 12V. the same time, DL2 show the excitement of the relay. If it doesn't, you just have to turn on the R6 trim cursor in such a way as to increase the sensitivity. If, however, the circuit was too sensitive, you must turn the trimmer in reverse. when the desired sensitivity is reached, you only need to adjust, with the slider R14, the excitation time of the alarm relay (for example, a siren is triggered). Therefore, the system is in your working condition.