Searching for treasures, ancient relics and other interesting things for many is a rather popular type of hobby, along with fishing or hunting. This type of recreation can also be considered active, and for some, a metal detector is quite a good tool for making money, because in the ground you can find quite a large number of ferrous metals that are appreciated today. After all, there is a proverb that "we walk for the money."
In the store, even for a not very powerful metal detector, they sometimes ask for decent money. This article will discuss how you can assemble a metal detector with your own hands. This requires minimal skills in the field of working with electronics and a small (compared to buying a new metal detector scanty) investment.
Materials and tools for assembly:
- microcircuit K561LA7 or its analog;
- low-power low-frequency transistor (KT315, KT312, KT3102 are suitable, analogs: BC546, BC945, 2SC639, 2SC1815 and so on)
- any low-power diode (for example, kd522B, kd105, kd106 ...);
- three variable resistors (4.7 kOm, 6.8 kOm, 10 kOm with a switch);
- five fixed resistors (22 Ohm, 4.7 kOm, 1.0 kOm, 10 kOm, 470 kOm);]
- five ceramic or mica capacitors (1000 pF - 2 pcs., 22 nF -2 pcs., 300 pF);
- one electrolytic capacitor (100.0 μF x 16V);
- wire type PEV or PEL with a diameter of 0.6-0.8 mm;
- headphones from the player (or any low impedance);
- 9V battery.
Metal detector manufacturing process:
Step one. Hull and appearance devices
Due to the fact that searches often take place among branches, grass or in wet weather, the device must be reliably protected from the effects of all these factors. As a housing for electronics, you can use a soap or shoe polish box. The main thing is that the electronic part is reliably protected.
It is important to know that if you do not connect variable resistors (their cases) with the minus of the board, the device will generate interference. If everything is done correctly and a high-quality coil is made, no problems arise during the operation of the device. When you turn on the metal detector, a characteristic squeak should immediately appear in the headphones, it should respond to the frequency control knob. If this is not observed, then you need to choose a 10 kΩ resistor that is in series with the regulator, or choose a 300 pF capacitor in this generator. As a result, you need to align the frequencies of the search and reference oscillators.
You will need an oscilloscope to determine what frequencies the generator is producing. In total, the operating frequency can be in the range of 80-200 kHz. Measurements are made at pins 5 and 6 of the K561LA7 microcontroller.
There is also a protective diode in the system. It is needed in order to protect the electronics from incorrect battery inclusion.
Step two. Making a search coil
The coils are wound on mandrels with a diameter of about 15-25 cm. As a form, you can use a bucket or shuttle made of wire or plywood. The smaller the coil is, the less sensitivity it will have, it all depends on the purpose for which the metal detector will be used.
As for the wire, it can be a wire in varnish insulation such as PEV or PEL with a diameter of 0.5 to 0.7 mm. This wire can be found in old CRT TVs. In total, the coil contains 100 turns, you can wind from 80 to 120. From above, the whole thing is tightly wrapped with electrical tape.
When the coil is wound, a winding of a strip of foil is made over it, while leaving an area of 2-3 centimeters unwound. Foil can be found in some types of cables, and you can also get it from chocolates by cutting it into pieces.
Not insulated wire is wound over the foil, but best of all is tinned. The beginning of the wire ends up on the coil, and the other end is soldered to the body. From above, all this is again well wrapped with electrical tape.
Subsequently, the coil is attached to the dielectric as option will do non-foil textolite. Now the coil can be attached to the holder.
To connect the coil to the circuit, you need to use a shielded wire, the shield is connected to the body. Similar wires can be used to re-record music from a tape recorder. You can also use the bass cord to connect various devices to the TV.
Step three. Metal detector check
When the device is turned on, a characteristic noise can be heard in the headphones, the frequency must be adjusted with the regulator. As you bring the coil closer to metal, the noise in the headphones will change.
You can also remake the circuit in such a way that the metal detector is silent during operation, and the signal will appear only when metal appears under the coil. In this case, the frequency of the noise will tell you what size the object is and at what depth it is. But, according to the author, this approach greatly reduces the sensitivity of the metal detector, and it picks up only very large objects.
To get zero beats, you need to combine the two frequencies.
In this way, you can assemble a simple metal detector with your own hands. Of course, you can hardly find a real treasure with him, but collecting coins and those lost on the beach is quite possible. You can make two coils for the device, one for finding large objects, and the other for finding small ones.
Entertaining schemes
An original selection of circuits and entertaining solutions from amateur radio practice focused mainly on a novice electronics engineer
Magnetic Levitation looks amazing. You can make a diagram of such a device yourself and with your own hands. Within the framework of this article, we will consider simplest option magnetic levitation device circuits. You will spend no more than two hours on the assembly of the structure itself.
Of course, you can just start as pet an ordinary rooster and he is guaranteed to wake you up, but you can assemble this simple entertaining scheme.
The dawn alarm clock scheme is made on three digital microcircuits K561LA7. A phototransistor is used as a photosensor. The phototransistor and resistance R1 are voltage divider. The sensitivity of the phototransistor is adjusted by selecting the value of R1, the higher it is, the better the sensitivity to morning dawn. The C1 capacity is used to prevent false triggering of the circuit from accidental flashes of light. The larger it is, the lower the likelihood of the circuit being triggered by accidental lighting.
On the logic gates DD1.1 and DD1.2 of the K561LA7 microcircuit, a Schmitt trigger is made, which sets the switching of the logic level when the specified light level of the phototransistor illumination is reached, and DD1.3 inverts the signal. To switch the RS-flip-flop, assembled from logical "cubes" DD2.1 and DD2.2, a short pulse shaper is built on the chain of radio components R5, C3, VD1.
With the morning dawn, the luminous flux sharply increases the resistance of the photosensor, too, so at the tenth output DD1.3 there will be a logical zero in and the chain R5, C3, VD1 will form a short pulse along the difference. The RS flip-flop will switch to another state and a logical unit level will appear at the DD2.3 output, which starts the AF generator on the elements DD2.4, DD3.1-DD3.4.
To turn off the alarm, you need to press and hold the switch button for 15 seconds. When pressed, the sound will disappear immediately, but if the button is released earlier, it will start again. Muting the sound is schematically connected with the discharge of the previously charged capacitance C5 through the resistance R6. At the end of the capacitor discharge process, the RS-flip-flop will return to its original state, thereby blocking the further sound of the sound generator.
555 is a legendary timer series, which was one of the first integrated micro-assemblies. It carries about 20 transistors and is used to operate in two modes. In the mode of a timer and a square-wave generator directly.
In fact, everything is much simpler, a small electronic circuit responsive to any loud noise, including the whistle.
The circuit emits an intermittent sound signal for several seconds after a person makes a loud whistle from a distance of no more than seven meters. The first two inverters of the K561LN2 microcircuit are used to process electrical impulses generated by a miniature microphone of the Sosna type. A preamplifier circuit is built on element DD1.1, and a frequency filter at 1.8 kHz is made on DD1.2. The filter removes pickup from unwanted audio noise.
Further, the amplified and filtered signal goes to the input of the Schmitt trigger, assembled on the elements DD1.3 and DD1.6 of the same microcircuit, which changes the continuously changing signal into a set rectangular pulse... The output signal from the trigger controls the sound generator on DD1.4 and DD1.5 and through the first transistor the sound signal enters the piezoceramic emitter ZP-1. The tone of the sound can be adjusted by selecting the capacitor C5.
The generator is assembled according to the scheme of a symmetrical multivibrator, in one of the circuits feedback of which the voice coil of the BA1 direct radiation dynamic head is switched on.
The device works like this. Suppose at some point in time at the output of the element DD1.1 there is a logical level 1. Due to this, the capacitor C7, connected through the resistor R4 to common bus, is charging. The charging current creates a voltage drop across this resistor, which is perceived by the DD1.2 element as level 1. At the same time, level 0 is set at its output and the capacitor C2 is discharged. As the capacitor C1 charges, the voltage drop across the resistor R4 decreases. When this value becomes less than a certain value, the element DD1.2 switches and level 1 at its output creates a charging current of the capacitor C2, passing through the resistance of the voice coil BA1 and the resistor R2. The voltage drop across this resistor sets the output level of the DD1.1 element to 0, and the capacitor C1 is discharged. As the capacitor C2 is charged, the voltage across the resistor R2 decreases to the switching threshold of the element DD1.1, as a result of which level 1 appears at its output and the charge of the capacitor C1 begins. In this case, at the output of the element DD1.2, level 0 is set and the capacitor C2 is discharged. Then the cycle repeats. The charge / discharge current of the capacitor C2, passing through the voice coil BA1, is converted into sound.
Setting up the generator is reduced to setting the required sound tone by selecting the resistance of the resistors R1 and R2.
The device can use dynamic heads of any type with a voice coil resistance of 4 ... 8 Ohm and integrated circuits K155LA1, K155LA4, K155LN1, K155LA12.
The following device can be used as an alarm or horn for a mountain bike. It is a two-tone siren and consists of a clock generator on the elements DD1.1-DD1.3, two tone generators (the first on the elements DD2.1, DD2.2 and the second on the elements DD2.3, DD2.4), a matching stage with power amplifier on element DD1.4 and transistor VT1.
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The tone generators that determine the pitch of the siren are controlled by the clock as follows. Suppose that at some point in time at the output of the element DD1.2 there is level 0. Then the output of the element DD1.3 will be level 1, which is fed to the inputs of elements DD2.1, DD2.2 of the first tone generator. The generator is excited, and the signal from its output is fed to the input of the matching stage at the element DD1.4. To the second input of this element
comes level 1 from the output of the second tone generator. This is because the level 0 of the output of the DD1.2 element enters the inputs of the DD2.3, DD2.4 elements, causing the appearance of level 1 at their outputs. Entering the input of the matching stage from the second tone generator, level 1 allows the signal to pass to its output from the first tone generator, which is amplified by the transistor VT1 and converted by the dynamic head BA1 into sound waves.
When the signal levels at the outputs of the elements DD1.2 and DD1.3 change to the opposite, the second tone generator is turned on, and the first one is turned off. Thus, with the frequency of the clock generator, the frequency of the sound reproduced by the dynamic head BA1 will also change.
Setting up the device comes down to setting the clock generator frequencies with resistors R3, R4 and R5, R6 and adjusting the clock generator operating frequency with resistor R1. You can use transistors KT603, KT608, KT640, etc. with any letter indices and a dynamic head with a voice coil resistance of 4 ... 8 Ohm.
The device, the diagram of which is shown below, when installed on a bicycle, will increase traffic safety. It is designed to control direction indicators and emergency stop signals.
The generator circuit on the elements DD1.1-DD1.3 is familiar to you (see. P. 32) and does not need any explanations. Therefore, we will consider the operation of the device as a whole.
When one of the buttons SB1, SB2 is pressed, the supply voltage is supplied to one of the power amplification stages on transistors VT1 or VT2. At the same time, through the corresponding diode VD1 or VD2, power is supplied to the integrated circuit DD1, and the generator starts to work.
From the generator output, a signal with a frequency of about 1 Hz through a resistor R3 is fed to the bases of transistors VT1, VT2. The transistor to which the supply voltage is supplied opens with the same frequency. As a result, the direction indicator signal lamp (HL1 or HL2), included in the collector circuit of this transistor, flashes at the same frequency. The second lamp does not light up at this time, since the corresponding diode is turned on in the opposite direction and prevents the passage of current to the second power amplification stage.
If you press one of the SB1 or SB2 buttons while the contacts of the SA1 switch are closed, the supply voltage will be applied to both amplification stages and both lamps will flash, signaling an emergency stop.
The device is operated under rather harsh conditions (temperature, humidity, vibration, etc.), so please pay Special attention on the quality of installation and protection of the board from external influences. The power source of this device can be two A3336 batteries connected in series, or a standard bicycle dynamo connected to it through a power amplifier.
With regard to the application in the device electronic elements, then the integrated circuit K155LN1 can be replaced with K155LAZ, K155L H2, K155LNZ. Transistors - any, medium power with conductivity type p-p-p... Signal lamps work in a pulsed mode, so they operating voltage 2.5 ... 5 V.
The device, the diagram of which is shown in the figure, will allow you to "revive" a ship or car with an electric drive. A clock generator with an operating frequency of about 1 Hz is assembled on the elements DD1.1, DD1.2, resistors R1, R2 and capacitors C1, C2, which controls the tone generator (DD1.5, DD1.6, R3, R4, C3, C4), operating at a frequency of about 1 kHz. In addition, the clock generator controls the timing of the lighting of the HL1 and HL2 LEDs in sync with the change in the frequency of the tone generator.
Let's talk about controlling the tone generator in more detail. In this circuit, resistors R3, R4 are connected to the output of the clock generator. When the voltage levels at the output of the DD1.3 element change, the voltage levels on the capacitors C3, C4 also change and, consequently, the time of their charge / discharge and the frequency of the tone generator.
Setting up the device is reduced to setting the operating frequencies of the clock and tone generators with resistors R1, R2 and R3, R4.
As for the elements of the circuit, it is possible to use any logical elements with the help of which the negation function can be realized. Transistor VT1 can be of type KT603, KT608, etc. LEDs can be
replaced by SMN 6,3-20 incandescent lamps (in this case, resistors R5, R6 can be excluded from the circuit) or other type of LEDs.
A dynamic head of any type with a voice coil impedance of 4 ... 8 Ohm.
If desired, you can install a simple color music console in a cassette recorder or transistor receiver. Its diagram is shown in the figure.
The signal coming from the output of the corresponding device is fed to the base of the transistor VT1, which acts as a matching amplifier. At certain levels of input signals, elements DD1.1 and DD1.2 begin to work and lamps HL1, HL2 light up.
Establishing a set-top box is reduced to the installation by resistors R2 and R4 of such operating modes in which they are on the verge of burning.
Having collected two such circuits on one board, you will receive a color-music set-top box for a stereo apparatus. In addition, this device can be used as peak level indicators.
The device is mounted inside your device and connected through a parametric stabilizer to the internal power supply. The lamps are placed on the front panel and covered with light filters, the color of which you can choose.
The diagram of a device designed to create light effects "running fire" or "running shadow" is shown in the figure. Based on it, you can create various light indicators, decorate a Christmas tree, illuminate demonstration tablets, etc.
The circuit is an auto-generator of cells included in the ring - inverters, consisting of a resistor, a capacitor, a transistor and a logic element. For example, one of the cells is R5, C3, VT3, DD1.4. To increase the switching time, an integrating circuit is introduced into each cell. The transistors at the inputs of the inverters have a relatively large input impedance, which provides the required value of the signal delay time without increasing the parameters of the elements of the integrating circuit.
The operation of the device is as follows. For example, when power is applied, a logic level is set at the output of the inverter DD1.2. In this case, the capacitor C2 begins to charge through the resistance of the resistor R3. The charging time of a capacitor depends on the capacitance of the capacitor and the resistance of the specified resistor. When the voltage across the capacitor increases to a level of 0.5 ... 0.7 V, the transistor VT2 opens and level 0 enters the input of the inverter DD1.3, and level 1 appears at its output. At the same time, the charge of the capacitor C3 begins, and the process repeats. Thus, after a time equal to the product of the number of generator cells by the delay time of the signal through one cell, level 1 will appear at the output of DD1.1. Having entered the input of DD1.2, it causes the appearance of level 0 at its output. In this case, the LED HL1 lights up, and the capacitor C2 is discharged through the resistor R3, the output resistance of the element DD1.2 and the emitter junction of the transistor VT2. When the capacitor is discharged, the VT2 transistor closes and level 1 enters the input of the element DD1.3, causing the appearance of level 0 at its output, after which the HL2 LED lights up, and the capacitor C3 begins to discharge. Similarly, the inverters DD1.3-DD1.6 are switched (respectively, the LEDs HL3-HL6 turn on), after which level 0 at the output of the element DD1.1 will cause the appearance of level 1 at the output of DD1.2 and the cycle will repeat. Thus, during the operation of the circuit, sequential ignition and extinguishing of all LEDs occurs.
You can modify the circuit by changing the number of cells in the ring. In this case, the part of the circuit, including the resistor R1, the capacitor C 7, the transistor VT1 and the logic elements DD1.1, DD1.2, cannot be changed.
The device, the diagram of which is shown in the figure, allows you to realize a sound effect reminiscent of the clucking of a chicken. It includes a clock generator, two sound generators and a power amplifier on a VT2 transistor.
The clock generator is assembled on a transistor VT1 and elements DD1.1, DD1.2. Its frequency is determined by the resistance of the resistors R1 and R2 and the capacitance of the capacitor C1.
The use of a transistor in a clock generator is due to the fact that in order to obtain long pulses, it is necessary to increase the input impedance of the DD1.1 inverter. It should be borne in mind that the gain of the transistor VT1 also affects the pulse duration. Depending on its value, the resistance of the resistor R2 may be greater or less than that indicated in the diagram. Resistor R1 is used to adjust the pulse duration, and resistor R2 is the pause between them.
The clock generator controls the operation of the generator, assembled on the elements DD1.3, DD1.4, the pulse repetition rate of which is equal to 5 Hz. It is determined by the resistance of the resistor R3 and the capacitance of the capacitor C2. In turn, through the DD2.1 inverter, the clock generator controls the operation of the audio frequency signal generator on the elements DD2.2, DD2.3. The power amplifier is assembled on a VT2 transistor, the load of which is a voice coil of a dynamic head with a resistance of 4 ... 8 Ohm, a power of 0.1 ... 0.5 W.
When the supply voltage is applied, a clock generator starts to work, generating pulses of positive polarity with a duration of 2 ... 2.5 s with pauses of 1 s. From the output of this generator, the pulses enter the input of the element DD1.3 and start the second generator, which forms during this time packs of 4 - 5 pulses, which are inverted and start the sound generator. It, in turn, generates 4 - 5 sequences of pulses of sound frequencies, similar to the sounds "kud-kud-kud".
At the same time, the signal from the output of the clock generator through the resistor R4 periodically turns on and off the diode VD1, through which the capacitor C4 is charged, which affects the frequency of the sound generator. This produces a sound like “yes”. When properly tuned, the generators simulate the cackling of a chicken.
For those of you who, in addition to digital electronics, are engaged in the assembly of radio receivers or amplifiers, irreplaceable assistant in their repair and adjustment, there may be a probe for checking low-frequency and high-frequency paths. It contains two generators: low-frequency on elements DD1.3, DD1.4 and high-frequency on elements DD2.1, DD2.2. The probe has two outputs with the ability to adjust the amplitude of the signals on each of them from 0 to 2 V.
The generators are assembled according to the scheme of symmetrical multivibrators, to the outputs of which the launch units are connected. The need to use the latter is due to the fact that when power is applied, the multivibrator, for example, on elements DD1.3, DD1.4, will not start, since the charging current of capacitors C1 and C2, depending on their capacity and resistance of resistors R1, R2, will be quite small. Therefore, the voltage across none of the resistors can exceed level 1 and levels 1 will be present at both outputs of the multivibrator. the output of the element DD1.4 appears a logic 0 level and the multivibrator starts up.
This node does not affect the operation of the multivibrator in a steady state, since at one of the inputs of the DD1.1 element and, accordingly, at the output of the DD1.2 element, level 0 will always be present, which is equivalent to connecting the resistor R2 to the common bus. The second multivibrator starts up in the same way.
Low frequency signals from the output of the first multivibrator start the second multivibrator. At its output, pulses are formed, modulated in amplitude by a low-frequency signal. To eliminate the DC component, they are fed to the probe output through appropriate capacitors.
If the power supply of radio circuits is carried out from batteries, then it is necessary to ensure control over the degree of their charge. The simple device offered here will help you with this. It will automatically ensure that the voltage of the autonomous power source is within the permissible limits. The service life of the batteries and their energy parameters depend on this. Decreasing the voltage on the supply rails of devices using digital integrated circuits below a certain level (4.5 V) can cause them to malfunction.
The control device has two channels: the first one - on the DD1.1 element, the second - on the DD1.2, DD1.3 elements. The first channel is configured so that, at an input voltage of more than 5.25 V, a logical level 1 arrives at the DD1.1 element from the resistor R1. At the same time, the level 0 is set at the DD1.1 output, which turns on the HL1 LED and prohibits the operation of the DD1.4 element.
The second channel is triggered when the voltage at the input of the monitoring device is less than 4.75 V. At the same time, level 0 is set at the input of element DD1.2, and level 1 at the input of element DD1.3. Level 0 at the output of the element turns on the HL3 LED and prohibits the operation of the element DD1.4.
If the input voltage of the monitoring device is 4.75 .. .5.25 V, then the outputs of the elements DD1.1 and DD1.3 are levels 1, and at the output of the element DD1.4 there is level 0, which turns on the LED HL2. Thus, the device provides a constant visual information the voltage levels from the power supply to the digital device.
The amateur radio circuit is a device based on one K561TM2 microcircuit, consisting of two triggers. On trigger D1.1. a generator is made that generates pulses with a frequency of 16 Hz. On trigger D1.2. a frequency divider is made by two.
The K561LA7 microcircuit (or its analogs K1561LA7, K176LA7, CD4011) contains four logical elements 2I-NOT (Fig. 1). The logic of operation of the 2I-NOT element is simple - if there are logical ones at both of its inputs, then the output will be zero, and if this is not so (that is, at one of the inputs or at both inputs there is a zero), then the output will be one. Chip K561LA7 CMOS logic, this means that its elements are made on field-effect transistors, therefore, the input impedance of K561LA7 is very high, and the power consumption from the power source is very small (this also applies to all other microcircuits of the K561, K176, K1561 or CD40 series).
Figure 2 shows a diagram of a simple time relay with LED indication. Time counting starts at the moment the power is turned on by switch S1. At the very beginning, the capacitor C1 is discharged and the voltage across it is small (like a logical zero). Therefore, the output D1.1 will be one, and the output D1.2 will be zero. The HL2 LED will be on and the HL1 LED will not be on. This will continue until C1 is charged through the resistors R3 and R5 to a voltage that the D1.1 element understands as a logical unit.At this moment, a zero appears at the D1.1 output, and a unit at the D1.2 output.
The S2 button serves to restart the time relay (when you press it, it closes C1 and discharges it, and when you release it, C1 starts charging again). Thus, the timing starts from the moment the power is turned on or from the moment the S2 button is pressed and released. The HL2 LED indicates that the timing is running, and the HL1 LED indicates that the timing is complete. And the time itself can be set variable resistor R3.
On the shaft of the resistor R3, you can put a pen with a pointer and a scale on which you can sign the time values by measuring them with a stopwatch. With the resistances of the resistors R3 and R4 and the capacitance C1 as in the diagram, you can set the shutter speed from a few seconds to a minute and a little more.
The circuit in Figure 2 uses only two elements of the microcircuit, but it has two more. Using them, you can make the time relay sound at the end of the exposure.
Figure 3 shows a diagram of a time relay with sound. On the elements D1 3 and D1.4 a multivibrator is made, which generates pulses with a frequency of about 1000 Hz. This frequency depends on the resistance R5 and the capacitor C2. A piezoelectric "buzzer" is connected between the input and output of the element D1.4, for example, from an electronic clock or a telephone-tube, a multimeter. When the multivibrator works, it beeps.
You can control the multivibrator by changing the logic level at pin 12 of D1.4. When here zero the multivibrator does not work, and the "buzzer" B1 is silent. When the unit is. - B1 beeps. This pin (12) is connected to the output of the element D1.2. Therefore, the "buzzer" beeps when HL2 goes out, that is, sound alarm turns on immediately after the time relay expires.
If you do not have a piezoelectric "buzzer" instead of it, you can take, for example, a micro-speaker from an old receiver or headphones, a telephone set. But it must be connected through a transistor amplifier (Fig. 4), otherwise the microcircuit can be damaged.
However, if we do not need LED indication, we can again do with only two elements. Figure 5 shows a diagram of a time relay, in which there is only an audible alarm. While the capacitor C1 is discharged, the multivibrator is blocked by a logical zero and the "buzzer" is silent. And as soon as C1 is charged to the voltage of a logical unit, the multivibrator will start working, and B1 will beep. Moreover, the tone of the sound and the frequency of interruption can be adjusted.It can be used, for example, as a small siren or an apartment bell
A multivibrator is made on the elements D1 3 and D1.4. generating pulses of audio frequency, which are fed through an amplifier on a transistor VT5 to speaker B1. The tone of the sound depends on the frequency of these pulses, and their frequency can be controlled by the variable resistor R4.
A second multivibrator on elements D1.1 and D1.2 serves to interrupt the sound. It generates pulses of a much lower frequency. These pulses are sent to pin 12 of D1 3. When here a logic zero multivibrator D1.3-D1.4 is off, the speaker is silent, and when the unit is a sound. This produces an intermittent sound, the tone of which can be controlled by resistor R4 and the chopping frequency by R2. The sound volume is highly dependent on the speaker. A speaker can be almost anything (for example, a speaker from a radio receiver, telephone, radio, or even acoustic system from the music center).
Based on this siren, you can make burglar alarm that will turn on every time someone opens the door to your room (fig. 7).
