The working principle is as follows: When a piezoelectric element in the imposition of an AC voltage at both ends, the beginning of the vibration components. If you remove the excitation voltage, the vibration damping in a way will continue, until all stop. These residual vibration in the piezoelectric element to produce at both ends of the oscillation damping. If the excitation signal near the resonant frequency, the vibration will be stronger, the residual oscillations will continue much longer. Determine the actual resonant frequency is near the resonant frequency nominal try all the frequencies, and compare the various remnants of the duration of oscillation.

In this design, Microchip’s PIC18F452 microcontroller, through its I / O pin RB4 and RB3 drive piezoelectric components. The beginning of RB3 zero, RB4 is set to 1, each half cycle of the two overturned, resulting in a changing of the piezoelectric 0V DC offset voltage (VP). In 10 cycles, RB3 remain low, RB4 as an input for the statistical VP low – high and high – low conversions. B port enable “port change interrupt” functions of the time 10 ms, so that an interrupt service routine to increase counter readings, statistical changes in the number of piezoelectric voltage. Procedures for a list of the functions of a presentation. Procedures on the frequency of all possible repeat these steps and determine the number corresponding to the maximum frequency conversion, which is the resonance frequency. This method can be easily extended to the case of multi-resonance frequency.

1. Due to the limited space available in the circuit can only choose SMD passive buzzer  (original height-saving considerations, the high active), which implies the need for oscillation circuit, he can work.

2. Button for calls outside the lift up and down arrow button panel, in the same board, the working principle of the button press the button when it was the signal to be input to elevator control system, control system to determine if the response is the key output a signal to the button’s lamp lights (signal lights in the elevator to the floor running when the control system and then to clear) If you do not respond to the buttons do not light the lamp.

3 customers now take into account the blind use of buzzer signals the need to add, that is, when the blind by pressing one button, the control system when the output light signal, this time the work needs to trigger buzzer,click (about 200ms), but if a second time to the blind, he could not see the lights, I do not know has been in accordance with button-off, so even if a key has been registered, press the button this time, if at this time, you also need to buzzer about to tell the second button are registered blind. However, if the control cabinet is not pressing the button does not respond to their light output signal, at this time press the button buzzer is not loud.

4. Two buttons (the upper and lower) utility of a buzzer

To sum up the circuit is divided into two parts, the logic part of the button and buzzer driving circuit part

1. Button logic include the following signals, the key signal S1, the button lights L1, the next key signal S2, the next button lights L2, buzzer control signal Q

L1 relatively high priority, when a signal is triggered when the rising edge of the ring buzzer, when the L1 in the high when the signal S1 If the button is pressed when the rising edge, but also trigger buzzer, S2 L2 found in the group with the same conditions in the above will trigger buzzer, as the buzzer sound is only 200ms, a relatively short time, the competition between the two sets of button does not consider the time being.

2 buzzer driver, as part of the output of a logic level signal or trigger signal when the output of the circuit’s frequency of 200 ms square-wave signal of 2700HZ.

3. Due to button the signal is relatively simple power supply circuit board does not provide voltage conversion for 24V, in order to achieve these functions, please use the cheapest way to build circuits. Please expert guidance, did not say clearly, please point out the places.

Way to make the distinction between feedback piezoelectric film is generally divided into buzz-style buzz-chip feedback (self-excited-type) and No feedback-style buzz-chip (external excitation) two. Feedback-type buzz when the film is with feedback oscillator circuit Will generate a cavity resonance frequency and the same tone; without feedback-type films can buzz with External oscillator circuit, select any frequency sound.

Following two piezoelectric film buzz fixed by:

a.
Support the way around – the buzz film diameter fixed on the edge of the resonance cavity, the general non-mining

Feedback-type buzz films, and the buzz-chip with the frequency with cavity will have a higher
The sound pressure output generated by the external oscillator circuit to promote signal to buzzer sounds.

b.
Node to support the way – will buzz with the film fixed in about the same size in diameter ceramic ring
Structure. If properly designed resonator, and with the frequency of the correct type of feedback buzz films

Feedback circuit and is, the larger will be able to generate the sound pressure and the correct frequency.

The above are two ways to be buzz-chip bonded to silica gel in the institutions.

1. Waterproof sticker 2. Spools 3. Coil 4. Magnet 5. Base 6. Pin 7. Shell 8. Core 9. Sealing glue 10. A small metal plates 11. Vibrating membrane

12. Circuit board

The working principle of passive electromagnetic buzzer:

Ac signal through the bypass line in the stent in the stent core package produce a column of alternating magnetic flux, the alternating magnetic flux and magnetic flux for a constant stack, so that films of molybdenum to a given

The exchange of signals with the frequency of vibration and sound resonator. Products of the frequency response and sound pressure curve and the value gap, molybdenum films inherent vibration frequency (which can be rough refraction

For small film thickness of molybdenum), Shell (Tune Helmholtz resonance) frequency of the magnetometer magnetic wire is directly related to the diameter.

Composed of electromagnetic  buzzer  by electromagnetic oscillator, the electromagnetic coil, magnet, vibration, such as the composition of membrane and shell.

Access to power, the audio signal generated by oscillator current through the electromagnetic coil to generate magnetic fields of electromagnetic coils.

Membrane vibration in the electromagnetic coil and magnet interaction, the buzzer sound vibration periodically.

 (1) Preparation of electro-magnet M: about 6 cm in the bolts on the iron ring around the wire 100, line 5 cm for left-side lead, using transparent adhesive tape to stick a good coil, so as not to release the coil, and then it sticky plasters in a box, the solenoid on the well.

(2) Preparation of shrapnel P: from the iron box can cut a width of 2 centimeters long iron, bent at right angles to the electromagnet in the shrapnel of a lead then, the re-use plastic sheets to keep pace with shrapnel in the board .

(3) a paper clip to make contact with Q, use paper clips to elevate the book, with plastic sheets cement, leads to a wire connected circuit in Figure.

(4) regulation of M and the distance between P (through the mobile box), so that electro-magnet to attract shrapnel, regulating contact with the distance between fragments, so that they can just contact with electricity can be heard after the beep sound.

The structure of the principle of buzzer

1. Piezoelectric buzzer mainly Multivibrator, piezoelectric buzz films, impedance matching and a resonance box, shell, etc.. Some shell piezoelectric buzzer is also equipped with light-emitting diodes.

Multivibrator constituted by transistors or integrated circuits. When connected to the power (1.5 ~ 15V DC operating voltage), multi-harmonic oscillator start-up, output of 1.5 ~ 2.5kHZ audio signal, impedance matching device to promote film piezoelectric audible beep.

Piezoelectric film by buzz or niobium lead zirconate titanate piezoelectric ceramics of lead acid magnesium materials. Ceramic films on the silver-plated electrodes on both sides, by the polarization and aging treatment, with brass or stainless steel sheet film together.

2. Electromagnetic  buzzer by the oscillator, the electromagnetic coil, magnet, vibration, such as the composition of membrane and shell.

Access to power, the audio signal generated by oscillator current through the electromagnetic coil to generate magnetic fields of electromagnetic coils. Membrane vibration in the electromagnetic interaction between the coil and magnet, the vibration of vocal periodically.

Buzz passive electromagnetic inductive load devices are the ideal square wave input is usually recorded as being: VO-P.

Buzz passive pressure load is capacitive devices, the ideal square wave input is usually recorded as two-way: VP-P.

However, if the IC is the reverse, such as device 4049, from a non-door buzzer access input and output is also very desirable, but sometimes too small output power IC, the sound falls short of expectations.

If the buzzer is used as a loud alarm pressure, and two ordinary pin inductance also can not meet the requirements of the general three-tap inductor will generally boost for more than 10 times, and some shouted pressure may take more than 110dB to achieve low-power step-up transformer.

Active and passive buzzer  What is the difference?

Buzzer buzzer active and passive product of the fundamental difference between the requirements of the input signal is different;

The ideal of active work buzzer DC signal is usually marked as VDC, VDD, etc.. Buzzer because there are a simple oscillator circuit, the DC can be converted into a constant frequency pulse signal, from the surface is the alternating magnetic field, driven vibration pronunciation molybdenum films. However, in some active buzzer signal in a particular exchange for being able to work, only the exchange of signals in high voltage and frequency requirements, such work will not be adopted in general.

No internal passive buzzer drive circuit, and some companies and factories as the hearing, GB device called an audible. Passive buzzer signals the work of the ideal square wave. If the DC signal to the buzzer in advance is not to respond, because the magnetic circuit of a constant vibration of Mo films can not pronounce.

1. Waterproof sticker 2. Spools 3. Coil 4. Magnet 5. Base 6. Pin 7. Shell 8. Core 9. Sealing glue 10. A small metal plates 11. Vibrating membrane

12. Circuit board

The working principle of passive electromagnetic buzzer:

Ac signal through the bypass line in the stent in the stent core package produce a column of alternating magnetic flux, the alternating magnetic flux and magnetic flux for a constant stack, so that films of molybdenum to a given

The exchange of signals with the frequency of vibration and sound resonator. Products of the frequency response and sound pressure curve and the value gap, molybdenum films inherent vibration frequency (which can be rough refraction

For small film thickness of molybdenum), Shell (Tune Helmholtz resonance) frequency of the magnetometer magnetic wire is directly related to the diameter.

Composed of electromagnetic buzzer  by electromagnetic oscillator, the electromagnetic coil, magnet, vibration, such as the composition of membrane and shell.

Access to power, the audio signal generated by oscillator current through the electromagnetic coil to generate magnetic fields of electromagnetic coils.

Membrane vibration in the electromagnetic coil and magnet interaction, the buzzer sound vibration periodically.

Voltage, current, drive, size, connection / fixed the way, of course, more importantly, want to be the voice of (the size of the sound pressure, frequency of high and low),

Operating voltage: electromagnetic buzzer-style, from 1.5 to 24V

Piezoelectric buzzer from 3V to 220V are possible, but the general piezoelectric or proposals of more than 9V voltage to obtain a greater voice.

Current consumption:

Electromagnetic buzzer in accordance with the different voltages, from dozens to hundreds of mA are, the piezoelectric buzzer on the power of more than a few mA can be a normal action, and the buzzer starts , the moment the need to consume about three times the current;

Driving Mode:

Electromagnetic and piezoelectric buzzer has two kinds of self-excited, as long as access to the DC (DC) can be audible, because the driver has built-in line at the buzzer, and because of the different principles of action, Electromagnetic buzzer to use 1 / 2 square wave to drive, the use of piezoelectric square in order to have better sound output.

Size:

Buzzer will affect the size of the volume size, the high and low frequency, electromagnetic 5mm from the smallest to the largest 25mm,

Piezoelectric from 12mm to 50mm or larger have.

Connection:

There are common pin (DIP), wire (Wire), SMD (SMD buzzer), piezoelectric-type stars were also big way lock screws.

Sound Pressure:

Buzzer often 10cm test distance as the standard, doubling the distance, probably attenuation 6dB, contrary to shorten the distance will increase twice as 6dB, Electromagnetic buzzer to achieve about 85dB / 10cm level, piezoelectric style buzzer can be done on a very loud, frequent alarms, most are made of piezoelectric buzzer. to the Part Number JIN Ming, the largest amount of electromagnetic buzzer;

Integrated buzzer, sealing the bottom of epoxy buzzer, buzzer split, did not seal at the bottom of plastic, about the general frequency of 2000, must not be too tin furnace.

Rated operating voltage:
1.5V, 3.0V, 3.6V, 5V, 9V, 12V, 24V.

Piezoelectric Piezo buzzer:

Diameter, 10mm, 12mm, 14mm, 16mm, 17mm, … .. 50mm specifications are many.

Rated the frequency of self-excited type, containing the lines, E external drive said buzzer (external drive)

Buzzer divided by the installation:

P = Pin type (needle inserted buzzer), and W-Wire (wire-type buzzer), SMD’s buzzer (patch-type buzzer).

1 kinds of sub-section shape is the encapsulation of soft start (to start bonding), this buzzer cheaper (about 0.30 yuan market around this price is for reference only); this type of non-performance of buzzer stability, the more obvious environmental impacts, such as vibration during transport, the production line welding (this product can not have wave or dip tin), high temperature (60 degrees) or low (-20 degrees) environment use; and anti-poor, such as the surrounding magnetic elements (in the week, coil inductors, transformers, magnets, etc.), the above situation will affect the buzzer sound quality, ranging from sand change the sound or the sound does not ring when the ring re – no sound, the buzzer is more suitable for the use of low-end electronic products.
Section is divided into two kinds of body entrapment hard to start (combination of control to start), this buzzer affordable (roughly 0.45 yuan market, this price is for reference only); this buzzer stability than the first better. This buzzer is more suitable for mid-range electrical and electronic products.

The first three kinds of size is a single-tube encapsulation hard to start (to start a combination of tube), the buzzer on the price (market price of about 0.65-1.00 million, this price is for reference only) for this buzzer better environmental adaptability, and the Baptist may have been wave soldering tin, but the anti-interference performance is not ideal.

No. 4 is a hardware encapsulation type used to start two-pipe (combination of two pipes to start), the buzzer prices higher (1.00-2.00 yuan market, this price is for reference only) this type buzzer usually high temperature of the plastic shell and the anti-coil, magnetic ring to produce, buzzer on the environment to adapt to such a good performance, low non-performing. Suitable for the use of high-end electronic products.