Operation of the circuit. When you clap your hands or click, the carbon powder in the microphone moves and changes its resistance. In this case, at the connection point between the limiting resistor R1 and the microphone, an alternating component appears, which, through the separating capacitor C 1, is supplied to the base of transistor T 1. Transistor T1 is both an amplifier of alternating and direct voltage. With the help of resistor R2, transistor T1 is in a slightly open state. The variable component received at the base is amplified by a transistor and, from the collector through capacitor C2, goes to a doubler rectifier assembled on elements DD1, DD2, C3. Double the constant voltage accumulates on capacitor C3, which is discharged through the circuit: minus the capacitor, resistor R1, base-emitter T1, plus the capacitor. In this case, the transistor opens like an avalanche, relay P1 is activated, its contacts close for the duration of the sound signal. When setting up the operation of the circuit, sometimes it turns out that its sensitivity is too high; it is triggered by cars passing along the street or by waving a hand near the microphone. It all depends on the type of relay used. You can roughen the circuit by connecting a variable resistor in series with capacitor C1. In order to switch the load (light bulbs) using claps, it is necessary to add a trigger to the circuit. The circuit of such a trigger on a polarized relay is shown in Figure 2 - it has not been printed anywhere before.
When a sound signal is given (clap, click), the contacts of relay KP1 are temporarily closed. An alternating voltage of 220 V through the lamp L1, diode D1 with a positive half-cycle is applied to the end of the second winding of the RP-4 relay, pin 8, the beginning of the winding, pin 7, current limiter resistor R1, capacitor C1, closed contacts of the relay KR1, pin 220V. The charging current of capacitor C1 switches the relay armature to the left position according to the diagram, light bulb L1 lights up and light bulb L2 goes out, diode D1 is blocked by the relay contacts, and diode D2 is unlocked and ready for operation. When the next sound signal arrives, the contacts of relay P1 KR1 close. A voltage of 220 V through light bulb L2 and diode D2 is applied as a plus to the beginning of the first winding, contact 5, from the output of the winding, contact 6 goes to resistor R1 and recharges capacitor C1. A polarized relay switches the armature to the right contact in the circuit. Diode D2 is blocked, and diode D1 is ready for the next cycle. Light L1 goes out and light L2 lights up. Thus, when sound signals are received, the load switches alternately. In order for the trigger to perform the function of turning on and off only one light bulb, you need to exclude one of the light bulbs from the circuit, and instead turn on a series chain of a 0.33 μF x 300 V capacitor and a 5–10 kOhm, 2 W resistor. When setting up the operation of the trigger, it is necessary to adjust the armature of the polarized relay so that it switches well and is securely fixed in the right or left position.
The basis of an acoustic or, what is the same, sound relay is also an electronic relay, and the sensor of control signals is a microphone or some other converter of air sound vibrations into low-frequency electrical vibrations.
Rice. 260. Acoustic relay circuit.
The diagram of the simplest version of such an electronic machine is shown in Fig. 260. Look at her carefully. Much, if not all, here should be familiar to you. The microphone performs the function of a control signal sensor. Transistors V1 and V2 form a two-stage amplifier of AF oscillations created by the microphone, and diodes V3 and V4, connected according to a voltage doubling circuit, are a rectifier of these oscillations. A cascade based on transistor V5 with an electromagnetic relay in the collector circuit and a storage capacitor in the base circuit is an electronic relay. Incandescent lamp, connected to the power source by relay contacts K1.1, symbolizes the executive (control) circuit.
In general, the machine works like this. While the room where the microphone is installed is relatively quiet, transistor V5 of the electronic relay is practically closed, contacts K1.1 of the relay are open in series, and the actuator circuit lamp does not light up. This is the initial standby mode of operation of the machine. When an audio signal appears, such as noise or a loud conversation, the audio frequency vibrations created by the microphone are amplified by transistors V1 and further rectified by diodes V3, V4. The diodes are turned on so that the voltage they rectify goes to the base of the transistor in negative polarity and simultaneously charges the storage capacitor.
If the sound signal is strong enough and the storage capacitor is charged to voltage, then the collector current of transistor V5 will increase so much that the relay will operate and its contacts K1.1 will turn on the actuator circuit - the signal lamp will light up. The executive circuit will be turned on all the time until the same or slightly higher negative voltage is maintained on the storage capacitor and on the base of transistor V5. As soon as the noise or conversation in front of the microphone stops, the storage capacitor is almost completely discharged through the emitter junction of the transistor, the collector current will decrease to the original state, the relay will release, and its contacts, opening, will de-energize the actuator circuit.
Using a trimming resistor, you can change (like a volume control) the voltage of the signal coming from the microphone to the input of the AF amplifier, and thereby adjust the sensitivity of the acoustic relay.
The microphone function can be performed by a subscriber loudspeaker or a telephone capsule. The static current transfer coefficient of the transistors must be at least 30. An electromagnetic relay can be of the type , RKN with an operating current of up to . The power source voltage should be 25-30% greater than the operating voltage of the selected electromagnetic relay. Calculate the resistance and power dissipation of the resistor, depending on the signal lamp used, yourself.
When starting to set up and test the acoustic machine, place the trimmer resistor slider in the lower (according to the diagram) position and select a resistor to set the current in the collector circuit of the transistor. It must be less than the release current of the electromagnetic relay. Then connect another resistor with a resistance of 15-20 kOhm in parallel with the resistor. In this case, the collector current of the transistor should increase sharply, and the relay should operate. Remove this resistor - the collector current should decrease to its original value, the relay should release the armature, and the actuator circuit lamp should go out. This way you can check the functionality of the electronic relay of the machine.
Set the collector currents of transistors V1 and V2 by selecting resistors.
Then set the resistor slider to the upper (according to the diagram) position and quietly pronounce a drawn-out sound “a-a-a” in front of the microphone, the machine will work and turn on the executive circuit. He must respond even to a quiet conversation in front of a microphone, or to clapping his hands.
Try this experiment. In parallel to the capacitor, connect a second electrolytic capacitor with a capacity of rated voltage 6-10 V. Connect a milliammeter to the collector circuit of transistor V5 and, following its arrow, clap your hands. What happened? The collector current increased, but the electromagnetic relay did not work. Clap your hands 5-10 times in a row. With each clap, the collector current increases and, finally, the relay operates and turns on the actuator circuit. If the sound signals stop, then after some time the current in the collector circuit of the transistor will decrease to the original value, the relay will release and turn off the executive circuit.
What does this experience say? The electromagnetic relay of the machine began to operate and release with a time delay. This is explained by the fact that now it takes more time both to charge the storage capacitor and to discharge it. The conclusion suggests itself: by selecting the capacity of the storage capacitor, you can regulate the turn-on and turn-off times of the actuator circuit.
Where and how can such an acoustic relay be used? For example, use it as a “Hush” machine. To do this, the signal lamp of the executive circuit must be placed in a box, one of the walls of which is made of frosted glass, and the inscription “Quiet” is written on it. As soon as the noise level or the volume of conversation in the room exceeds a certain limit set by the trimmer resistor, the light display will immediately react to it. Or, say, you can install an automatic machine together with a small-sized microphone on a self-propelled model or toy, and its microelectric motor can be included in the actuator circuit instead of an incandescent signal lamp. A few clapping hands or a voice command - and the model begins to move forward. How else? Think about it!
The next example of automation...
A couple of weeks ago, an LED panel for room lighting was assembled and it was decided to assemble an acoustic switch for it, and today I want to look at perhaps the simplest acoustic switch circuit.
The scheme was found on one of the bourgeois sites and slightly altered. The device allows you to turn the power circuit on and off with a clap. I intend to use it to turn on the lights. The device is quite sensitive thanks to a double amplifier using low-power transistors. It responds to clap at a distance of 5 meters from the microphone. All parts were replaced with domestic ones.
The microphone amplifier uses domestic transistors of the KT 315 series with any letter or index. The final stage uses a powerful transistor switch based on a bipolar transistor of the KT 818 series, all other details are the same as in the original circuit. You can exclude the relay from the circuit and connect a load in its place, but this is only in cases where you need to control loads with power up to 12 volts; if you need to control loads with power from the network, you can’t do without a relay. At the moment of clap, the microphone receives the wave, and as a signal it is sent to a power amplifier, which alternately amplify the signal received from the microphone. The amplified signal arrives at the base of the switch, its magnitude is sufficient to trigger the transistor, and at this moment the junction of the transistor opens and conducts a current that powers the connected load or relay.
When assembling, observe all the ratings of the parts; even a slight slope can lead to abnormal operation of the switch. The device responds not only to pops, but also to low-frequency noise (powerful bass, etc.).
The supply voltage range is from 4 to 16 volts, power only from stabilized DC voltage sources and under no circumstances use switching power supplies, the device will not work with them!
For the trial version, the device was mounted mounted, then it will be transferred to the board, the main thing is that everything works without failures.
Relay circuits are used in automatic control systems: to maintain a given temperature, light, humidity, etc. Such circuits are usually similar and contain a sensor, a threshold circuit and an actuator or indicator device as mandatory components (see the list of references).
Relay circuits react when the controlled parameter exceeds a given (set) level and turn on the actuator (relay, electric motor, one or another device).
It is also possible to notify with a sound or light signal that the controlled parameter has gone beyond the permissible level.
Transistor thermal relay
The thermal relay (Fig. 1) is based on a Schmitt trigger. A thermistor (a resistor whose resistance depends on temperature) is used as a temperature sensor.
Potentiometer R1 sets the initial bias on thermistor R2 and potentiometer R3. By adjusting it, the actuator (relay K1) is activated when the resistance of the thermistor changes.
Rice. 1. Scheme of a simple thermal relay using transistors.
Not only a relay, but also a low-current incandescent lamp can be used as a load in this and other circuits in this chapter.
You can turn on an LED with a series current-limiting resistor of 330...620 Ohms, a sound generator, an electronic siren, etc.
When using a relay, the contacts of the latter can include any load electrically isolated from the sensor circuit: a heating element or, conversely, a fan.
To protect the output transistor from voltage pulses that occur when switching the relay winding (inductive load), it is necessary to connect a semiconductor diode in parallel with the relay winding.
So, in Fig. 1 anode of the diode must be connected to the bottom terminal of the relay winding according to the diagram, the cathode - to the power bus. Instead of a diode, a zener diode or capacitor can be connected with the same result.
Thermal relay on a thyristor
The thermal relay [MK 6/82-3] (Fig. 2) has a self-blocking output stage based on a thyristor.
Rice. 2. Schematic diagram of a thermal relay based on a transistor and a thyristor.
This leads to the fact that after the circuit is triggered, the alarm can only be turned off after a short-term power outage to the device.
Simple temperature indicator
The thermal relay (Fig. 3), or, more precisely, the thermal indicator, is made according to a bridge circuit [VRL 83-24]. When the bridge is balanced, none of the LEDs light up. As soon as the temperature rises, one of the LEDs will turn on.
Rice. 3. Schematic diagram of a simple thermal indicator using one transistor and LEDs.
If the temperature, on the contrary, decreases, another LED will light up. To distinguish in which direction the temperature is changing, you can use a red LED to indicate an increase in temperature, and a yellow (or green) LED to indicate a decrease. To balance the circuit, it is better to include a potentiometer instead of resistor R2.
Transistor photo relay
The photo relay (Fig. 4) differs from the thermal relay (Fig. 16.1) in that instead of a thermistor, a photosensitive device (photodiode or photoresistor) is used.
Rice. 4. Schematic diagram of a simple photo relay using transistors.
Photo relay with two-stage amplifier
Photo relay circuit shown in Fig. 5 contains a two-stage DC amplifier made of transistors of different conductivity types.
Rice. 5. Schematic diagram of a photo relay with a two-stage amplifier.
When the electrical resistance of the photodiode and, accordingly, the bias at the base of the transistor VT1 changes, the collector current of the output transistor of the amplifier VT2 will increase, and the voltage across the resistor R2 will increase.
As soon as this voltage exceeds the breakdown voltage of the threshold element - the semiconductor zener diode VD2, the final stage on the transistor VT3 is turned on, controlling the operation of the actuator (relay).
The use of a threshold element (semiconductor zener diode) in the circuit increases the clarity of the photo relay operation.
Photo relay with sound alarm
The photo relay (Fig. 6) is not fully such, since it responds to changes in illumination by smoothly changing the frequency of the generated oscillations.
Rice. 6. Schematic diagram of a photo relay with a sound alarm.
At the same time, this device can work in conjunction with frequency-measuring devices, frequency-selective relays, and signal changes in illumination with the height of the sound signal, which can be very important for the visually impaired.
Humidity relay circuit, liquid level relay
The humidity relay or liquid level relay (Fig. 7), like some of the above circuits, is based on a Schmitt trigger [MK 2/86-22].
Rice. 7. Schematic diagram of a humidity relay, liquid level relay.
The device response threshold is set by adjusting potentiometer R3. The humidity sensor contacts are made in the form of copper (Ci) and iron (Fe) rods immersed in the ground.
When the moisture content in the ground changes, the electrical conductivity of the medium and the resistance between the electrodes change. As the bias at the base of transistor VT1 increases, it opens.
The collector and emitter currents of the transistor increase, which leads to an increase in the voltage on the potentiometer R3 and, accordingly, to switching the trigger.
The relay is activated. The device can be configured to reduce the electrical conductivity of the earth below a specified norm. Then, when the actuator is triggered, the automatic watering system for the soil (plants) is turned on.
Time relay
The time relay (Fig. 8) is described in the book by P. Velichkov and V. Hristov (Bulgaria). A short press on the SA1 button discharges the timing capacitor C1 and the device begins the “time countdown”.
Rice. 8. Schematic diagram of a time relay using transistors.
As the capacitor charges, the voltage on its plates gradually increases. As a result, after some time the relay will operate and the actuator will turn on.
The charging rate of the capacitor, and therefore the holding time (exposure time), can be changed with potentiometer R1. The relay provides a maximum exposure time of up to 10 seconds with the parameters of the elements indicated on the diagram. This time can be increased by increasing the capacitance of capacitor C1 or the resistance of potentiometer R1.
It is worth noting that for such simple “analog” timer circuits, the stability of the time interval is low. In addition, it is impossible to increase the capacitance of the timing capacitor indefinitely, since its leakage current increases noticeably.
Such a capacitor is unacceptable in “analog” timer circuits. It is also impossible to significantly increase the exposure time due to the resistance of potentiometer R1, since the input resistance of subsequent stages, unless they are made using field-effect transistors, is small.
Analog timers (time relays) are widely used in photo printing to set the time for performing any procedures. These devices are used, for example, to produce silver-ionized water.
A relay that responds to voltage level
Voltage relays (Fig. 9, 10) are used to control the charge or discharge of batteries, batteries, control the supply voltage, and maintain the voltage at a given level. The circuits described in the book by P. Velichkov and V. Hristov are designed to control the discharge (Fig. 9) or overcharge (Fig. 10) of the battery.
Rice. 9. Schematic diagram of a relay for monitoring battery discharge.
Rice. 10. Schematic diagram of a relay for monitoring battery overcharge.
If necessary, the response voltage of these devices can be changed. The response threshold is set by the type of zener diode. To change the operating threshold of such relays within small limits, 1 - 3 germanium Shch9) or silicon (KD503, KD102) diodes can be connected in series with the zener diode in the forward direction.
The cathodes of the diodes should “look” towards the base of the input transistor. A germanium diode shifts the threshold by about 0.3 V, and a silicon diode by 0.5 V.
For a chain of two or three diodes, these values are doubled (tripled). Intermediate voltage values can be obtained by connecting germanium and silicon diodes in series (0.8 V).
Acoustic relay
An acoustic relay (Fig. 11, 12) is used to control noise levels, as well as as part of security alarm systems [B.S. Ivanov, M 2/96-13]. Among other things, such circuits are often used in communication systems - in voice control devices for a communication channel.
Rice. 11. Schematic diagram of an acoustic relay.
Rice. 12. Schematic diagram of an acoustic relay using transistors.
So, during a conversation, the radio station or communication line switches from receiving to transmitting automatically and without operator intervention. The device contains an audio signal sensor - a microphone, which can be used as a conventional microtelephone capsule, a low-frequency amplifier, a detecting and executing (relay) device.
The ULF gain determines the sensitivity of the acoustic relay. A sound-collecting horn can be installed on the microphone to increase the directional properties of the acoustic relay. A resonant filter, switched on after the ULF, allows the acoustic relay to respond only to a sound of a certain frequency and ignore other sounds.
Literature: Shustov M.A. Practical circuit design (Book 1), 2003.
set NS048
Based on this acoustic relay, you can independently create security systems, as well as other devices that can respond to sound, for example: automatic sound lighting switches, systems that track the source of sound and, of course, “smart” toys.
Specifications
Supply voltage [V] 9-12
Maximum current consumption [mA] 60
Description of the operation of the acoustic relay
The appearance of the acoustic relay and its electrical circuit are shown in Rice. 1 And Rice. 2.
Rice. 1. Appearance of the acoustic relay
The electrical circuit consists of two main parts: analog and digital. The analog part includes two operational amplifiers A1 and A2, the digital part includes inverters N1…N4.
From the output of the electret microphone, an electrical audio frequency signal is supplied to the input of the first operational amplifier A1, which matches the microphone with the output stage assembled on the operational amplifier A2. The sensitivity of the circuit as a whole is set by trimming resistor P1. The gain of the output stage is determined by the ratio of resistances R7, P1 and R5.
The amplified audio frequency signal is fed to the driver circuit. As it passes through inverter N1, capacitor C2 is charged to a logical one voltage at the lower input of inverter N2 in the circuit. As soon as the capacitor is charged, the output N2 changes the logical level to the opposite one, thereby forcing the trigger circuit built on the N3N4 inverters to switch to the opposite state. A logical one appears at the output of inverter N4, opening transistor TR1. As a result, LED D2 lights up and the winding of the electromagnetic relay K1 is connected to the power source, which switches the load through contacts K 1.1. Diode D1 is necessary to protect the transistor during its switching from current surges resulting from transient processes in the electromagnetic relay winding.
If the electret microphone does not pick up acoustic vibrations for some time, the variable component at the output of operational amplifier A2 will be zero, which leads to the appearance of a logical zero at the output of inverter N1. Capacitor C2 begins to discharge through resistor R1. After the discharge process is terminated, driver N2 resets the trigger circuit to its original state, which leads to the closure of transistor TR1, and consequently, de-energization of the electromagnetic relay winding. The load is switched off. The acoustic relay goes into standby mode.
Acoustic relay assembly
Before assembling the acoustic relay, carefully read the recommendations for installing electronic circuits given at the beginning of this book. This will help avoid damage to the printed circuit board and individual circuit elements. The list of set elements is given in Table 1.
Table 1. List of elements of the NS048 set
|
Characteristic |
Title and/or note |
||
|
Brown, green, red* |
|||
|
R2, R9, Rll, R12 |
Yellow, purple, red* |
||
|
Brown, grey, orange* |
|||
|
Brown, black, orange* |
|||
|
Brown, black, brown* |
|||
|
Red red, red* |
|||
|
Orange, white, brown* |
|||
|
Trimmer resistor |
|||
|
100 µF, 16/25 V |
Capacitor |
||
|
10 µF, 16/63 V |
Capacitor |
||
|
Capacitor (22p - marking) |
|||
|
Capacitor (104 - marking) |
|||
|
Capacitor (56 - marking) |
|||
|
Red LED |
|||
|
Transistor. Replacement BC548 NPN |
|||
|
7400 or 74LS00 |
Chip |
||
|
LF353 or TL082 |
Chip |
||
|
Electret microphone |
|||
|
Printed circuit board |
|||
|
Sockets for microcircuits |
|||
|
Relay 6V/2A |
|||
|
Battery connector |
|||
|
Pin contacts |
|||
|
* Color coding on resistors. |
|||
Form the element leads, install them on the board and solder the leads. Connect the power supply and load according to the diagram shown on Rice. 3.
Rice. 3. Connection diagram of the power source and load to the acoustic relay board
Turn on the power to the acoustic relay electronic circuit. Use resistor P1 to set the required sensitivity of the device. Now everything is ready for successful operation of the acoustic relay.
In the event that you want to make a structurally complete device based on the NS048 kit, you can select a suitable stabilized power supply and housing for the acoustic relay in the catalog given in this book or on the website www.masterkit.ru. The design of the board provides for its installation in the case: for this there are mounting holes along the edges of the board for 03 mm screws. A correctly assembled device does not require additional configuration for operation.
Even a novice radio amateur can assemble such an acoustic relay. The NS048 kit is already fully equipped with everything you need, so all that remains is to install the components. Problems that arise during assembly can be discussed at the conference at http://www.masterkit.ru, and questions can be asked at: [email protected].
NS048 sets, as well as other sets from the MASTER KIT catalog, can be purchased in radio parts stores or at radio markets.
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