Scheme. Capacitive proximity sensor
Today, presence sensors have become very fashionable to detect movement when a person moves around the room.
When connecting such a device to lighting fixtures, You'll get automatic system by turning on the light. Almost anyone can assemble a presence sensor to detect a person on their own. And here the assembly diagram will be the main one. You will learn everything about the assembly process from this article.
Principle of operation
The first thing you need to know when self-assembly such a device is the principle of its operation.
Note! Many people confuse such devices with motion sensors. But these are different models.
The operating principle of the device is based on the sensor’s response to the location of a person or large animal. The operation of the device is based on the Doppler effect - a change in wavelength and frequency. These changes are recorded by the sensor and transmitted to the device to further turn on the lighting or sound signal. Moreover, the signal arrives at the sensor regardless of whether the object moves or remains motionless. The device is equipped with an antenna and a generator. Without the presence of a reflective antenna signal, the device is in sleep mode. The operating diagram is shown below.
When connecting the device to a light source, in a situation where any object appears in work area the light is activated. At the same time, to turn on the lighting as such, there is no need for movement (even a slight one).
Where is it used?
The presence sensor is actively used today in the following areas:
- system " smart House» to turn on the light automatically (the connection diagram is shown below). In this situation, it allows you to save electricity consumption significantly;
Connection diagram
- security systems;
- robotics;
- various production lines;
- video surveillance systems;
- to control electricity consumption, etc.
In addition, interactive toys equipped with similar devices are increasingly appearing. But in most cases, when the device reacts, there is no need to turn on the light. Such products can respond to temperature, ultrasound, object weight and many other parameters. The lighting does not turn on here. The device reacts, for example, by turning on the sound or transmitting a signal to a portable mobile device (for modern models).
Such developments are especially indispensable in security system. But not every person can afford to purchase such a device. They are quite expensive and may not be affordable. Therefore, some people make such devices with their own hands.
Let's start assembling
In order to assemble the sensor, you will need the diagram below.
In addition to this you will need:
- microwave generator;
- transistor KT371 (KT368), which must be pre-amplified by KT3102;
- comparator;
- microcircuit K554CA3.
All necessary components for assembly can be found on the radio market or in specialized electronics stores.
According to this diagram, it is necessary to assemble and solder the above elements.
According to the given diagram, the sensor will work like this:
- the generator produces a microwave signal;
- then it is transmitted to the whip antenna;
- then the signal is reflected from an object moving in the controlled area;
- the result is a frequency shift;
- then it is returned to the antenna and microwave generator.
At this stage it will operate as a direct conversion receiver. This is due to the fact that the received signal is converted into infrasonic (low frequency).
After signal conversion, the following happens:
- now the low-frequency vibrations already received, reaching the pre-amplifier, are amplified;
- they are then transmitted to the comparator and converted into pulses (rectangular).
If the signal is not reflected, then a high level voltage is obtained at the output of the comparator.
A trimmer capacitor is needed to set the frequency. It must be equal to the resonant frequency of the antenna.
Note! This parameter should be selected according to the maximum sensitivity of the sensor.
From a constructive point of view, the device must be made on a printed circuit made of fiberglass. The board must be placed on a plastic case.
Printed circuit (example)
You can use a piece of rigid wire as an antenna. For its manufacture it is better to choose copper wire. We solder it to the contact pad of the resulting board. The antenna output is carried out through the output on the housing. Experts recommend placing the antenna vertically.
Remember that any shielding objects should not be placed in the immediate vicinity of a self-assembled sensor. In addition, you should know that for normal functioning of a soldered product, its common wire must have a capacitive connection to the ground.
Final stage
After you have installed the compact device, it should be suspended from inside doors, as close as possible to door handle And door lock. The product can also be placed in other places. The main thing is that the controlled area is sufficient.
During installation, it is necessary to ensure that the length of the conductors and element leads is minimal. This will avoid interference, which could result in the device not working properly.
Following the instructions and diagram provided, it is relatively easy to assemble a presence sensor with your own hands. The main thing is to mount all the components in the right order.
Choosing the right autonomous sensors for driving with a siren
Review and installation of the remote control for radio control of light
Motion sensors - incredible convenient thing, which allows you to control the light in the room or control the opening and closing of doors, and can also notify you of unwanted guests. In this article we will tell you how to make a motion sensor with your own hands at home and look at the area possible application device data.
Briefly about sensors
One of the most simple types sensors - limit switch or self-resetting button (without fixation).
It is installed near the door and reacts to its opening and closing. Using a simple circuit, this device turns on the light in the refrigerator. It can be equipped with a storage room or hallway vestibule, a door at the entrance, a duty room LED backlight, use this switch as an alarm that will notify you when the door is opened or closed. Disadvantages of the design may be difficulties in installation, and sometimes unpresentable appearance.
Devices based on magnets can be seen on the doors and windows of protected objects. Their operating principle is very similar to that of a button. A reed switch can open or connect contacts when a conventional magnet is brought to it. Thus, the reed switch itself is installed on the doorway, and the magnet is hung on the door. This design looks neat and is used more often than regular button. Lack of devices in narrow specialized application. They are not suitable for monitoring open areas, squares, and passages.
For open passages, there are devices that respond to changes in the environment. These include photo relays, capacitive (field sensors), thermal (PIR), sound relays. To record the intersection of a certain area, control an obstacle, or the presence of movement of an object in the overlap area, photo or sound echo devices are used.
The operating principle of such sensors is based on the formation of a pulse and its recording after reflection from an object. When an object enters such a zone, the characteristic of the reflected signal changes, and the detector generates a control signal at the output.
For clarity, a schematic diagram of the operation of a photo relay and sound relay is presented:
As a transmitting device in optical sensors Infrared LEDs are used, and phototransistors are used as a receiver. Sound sensors operate in the ultrasonic range, so their operation appears silent to our ears, but each of them contains a small emitter and catcher.
For example, it is great to equip a backlit mirror with a motion detector. The lighting will turn on only at the moment when a person is directly next to it. Don't want to make one yourself?
Assembly diagrams
Microwave
To control open spaces and monitor the presence of objects in the desired area, there is a capacitive relay. The operating principle of this device is to measure the amount of radio wave absorption. Everyone has observed or been a participant in this effect when, approaching a working radio receiver, the frequency on which it operates gets lost and interference appears.
Let's talk about how to make a microwave-type motion sensor. The heart of this detector is a radio microwave generator and a special antenna. 
On this schematic diagram presents a simple way to make a microwave motion sensor. Transistor VT1 is a high-frequency generator and also a radio receiver. The detector diode rectifies the voltage by applying a bias to the base of transistor VT2. The windings of transformer T1 are tuned to different frequencies. In the initial state, when the antenna is not affected by external capacitance, the amplitudes of the signals are mutually compensated and there is no voltage on the detector VD1. When the frequency changes, their amplitudes are added and detected by a diode. Transistor VT2 begins to open. As a comparator for clear processing of the “on” and “off” states, thyristor VS1 is used, which controls a 12-volt power relay.
Below is an effective diagram of a presence relay using available components, which will help you assemble a motion detector with your own hands or simply be useful for getting acquainted with the device.
Thermal
Thermal IR (PIR) is the most common sensor device in the business sector. This is due to cheap components, simple assembly scheme, lack of additional complex settings, wide temperature range work.
The finished device can be purchased at any electrical goods store. Often this sensor is equipped with lamps, alarm devices and other controllers. However, now we will tell you how to make a thermal motion sensor at home. Simple scheme to repeat looks like in the following way:
A special thermal sensor B1 and a photo element VD1 make up an automated lighting control complex. The device starts working only after dusk; the response threshold can be set with resistor R2. The sensor connects the load when a moving person enters the control zone. The time of the built-in timer for shutdown can be set using the R5 regulator.
Homemade module for Arduino
An inexpensive sensor can be made from special ready-made boards for a radio designer. This way you can get a fairly miniature device. For assembly we will need a motion sensor module for Arduino microcontrollers and a single-channel relay module.
Each board has a three-pin connector, VCC +5 volts, GND -5 volts, OUT output on the detector and IN input on the relay board. In order to make a device with your own hands, you need to supply 5 Volts (plus and minus) to the boards from the power source, for example, from a phone charger, and connect out and in together. Connections can be made using connectors, but it will be safer to solder everything. You can follow the diagram below. A miniature transistor, as a rule, is already built into the relay module, so there is no need to install it additionally.
When a person moves, the module sends a signal to the relay and it opens. Please note that there is a high and low level. It must be selected based on the signal the sensor produces at the output. The finished detector can be placed in the housing and masked in the desired location. Additionally, we recommend watching videos that clearly demonstrate instructions for assembling homemade motion sensors at home. If you still have any questions, you can always ask them in the comments.
Capacitive sensor is one of the types contactless sensors, the principle of operation of which is based on a change in the dielectric constant of the medium between the two plates of the capacitor. One plate is a touch sensor circuit in the form of a metal plate or wire, and the second is an electrically conductive substance, for example, metal, water or the human body.
When developing a system for automatically turning on the water supply to the toilet for a bidet, it became necessary to use a capacitive presence sensor and switch that are highly reliable, resistant to changes in external temperature, humidity, dust and supply voltage. I also wanted to eliminate the need for a person to touch the system controls. The requirements presented could only be met by touch sensor circuits operating on the principle of changing capacitance. Ready scheme I couldn’t find one that satisfied the necessary requirements, so I had to develop it myself.
The result is a universal capacitive touch sensor that does not require configuration and responds to approaching electrically conductive objects, including a person, at a distance of up to 5 cm. The scope of application of the proposed touch sensor is not limited. It can be used, for example, to turn on lighting, systems burglar alarm, determining the water level and in many other cases.
Electrical circuit diagrams
To control the water supply in the toilet bidet, two capacitive touch sensors were needed. One sensor had to be installed directly on the toilet; it had to produce a logical zero signal in the presence of a person, and in the absence of a logical one signal. The second capacitive sensor was supposed to serve as a water switch and be in one of two logical states.
When the hand was brought to the sensor, the sensor had to change the logical state at the output - from the initial one state to the logical zero state, when the hand was touched again, from the zero state to the logical one state. And so on ad infinitum, as long as the touch switch receives a logical zero enabling signal from the presence sensor.
Capacitive touch sensor circuit
The basis of the capacitive sensor presence sensor circuit is a master rectangular pulse generator, made according to classic scheme on two logical elements of the microcircuit D1.1 and D1.2. The generator frequency is determined by the ratings of the elements R1 and C1 and is selected around 50 kHz. The frequency value has virtually no effect on the operation of the capacitive sensor. I changed the frequency from 20 to 200 kHz and visually did not notice any effect on the operation of the device.
From pin 4 of microcircuit D1.2, a rectangular signal through resistor R2 is supplied to inputs 8, 9 of microcircuit D1.3 and through variable resistor R3 to inputs 12,13 of D1.4. The signal arrives at the input of the D1.3 microcircuit with a slight change in the slope of the pulse front due to the installed sensor, which is a piece of wire or metal plate. At input D1.4, due to capacitor C2, the front changes for the time required to recharge it. Thanks to the presence of trimming resistor R3, it is possible to set the pulse edge at input D1.4 equal to the pulse edge at input D1.3.
If you bring your hand or hand close to the antenna (touch sensor), metal object, then the capacitance at the input of the DD1.3 microcircuit will increase and the front of the incoming pulse will be delayed in time relative to the front of the pulse arriving at the input of DD1.4. In order to “catch” this delay, the inverted pulses are fed to the DD2.1 chip, which is a D flip-flop that works as follows. Along the positive edge of the pulse arriving at the input of microcircuit C, the signal that was at that moment at input D is transmitted to the output of the trigger. Consequently, if the signal at input D does not change, the incoming pulses at the counting input C do not affect the level of the output signal. This property of the D trigger made it possible to make a simple capacitive touch sensor.
When the antenna capacitance, due to the approach of the human body to it, at the input of DD1.3 increases, the pulse is delayed and this fixes the D trigger, changing its output state. LED HL1 is used to indicate the presence of supply voltage, and LED HL2 is used to indicate proximity to the touch sensor.
Touch switch circuit
The capacitive touch sensor circuit can also be used to operate the touch switch, but with a little modification, since it needs not only to respond to the approach of the human body, but also to remain in a steady state after the hand is removed. To solve this problem, we had to add another D trigger, DD2.2, to the output of the touch sensor, connected using a divider by two circuit.
The capacitive sensor circuit has been slightly modified. To exclude false alarms, since a person can bring and remove his hand slowly, due to the presence of interference, the sensor can output several pulses to the counting input D of the trigger, violating the required operating algorithm of the switch. Therefore, an RC chain of elements R4 and C5 was added, which for a short time blocked the ability to switch the D trigger.
Trigger DD2.2 works in the same way as DD2.1, but the signal to input D is supplied not from other elements, but from the inverse output of DD2.2. As a result, along the positive edge of the pulse arriving at input C, the signal at input D changes to the opposite. For example, if in the initial state there was a logical zero at pin 13, then by raising your hand to the sensor once, the trigger will switch and a logical one will be set at pin 13. The next time you interact with the sensor, pin 13 will again be set to logical zero.
To block the switch in the absence of a person on the toilet, a logical unit is supplied from the sensor to the R input (setting zero at the output of the trigger, regardless of the signals at all its other inputs). A logical zero is set at the output of the capacitive switch, which is supplied through the harness to the base of the switch-on key transistor solenoid valve in the Power and Switching Unit.
Resistor R6, in the absence of a blocking signal from the capacitive sensor in the event of its failure or a break in the control wire, blocks the trigger at the R input, thereby eliminating the possibility of spontaneous water supply in the bidet. Capacitor C6 protects input R from interference. LED HL3 serves to indicate water supply in the bidet.
Design and details of capacitive touch sensors
When I began to develop a sensor system for water supply in a bidet, the most difficult task seemed to me to be the development of a capacitive occupancy sensor. This was due to a number of installation and operation restrictions. I didn’t want the sensor to be mechanically connected to the toilet lid, since it needs to be removed periodically for washing, and not to interfere with the sanitization of the toilet itself. That’s why I chose a container as a reacting element.
Presence sensor
Based on the above published diagram, I made a prototype. The parts of the capacitive sensor are assembled on a printed circuit board; the board is placed in a plastic box and closed with a lid. To connect the antenna, a single-pin connector is installed in the case; a four-pin connector RSh2N is installed to supply the supply voltage and signal. The printed circuit board is connected to the connectors by soldering with copper conductors in fluoroplastic insulation.
The capacitive touch sensor is assembled on two KR561 series microcircuits, LE5 and TM2. Instead of the KR561LE5 microcircuit, you can use the KR561LA7. 176 series microcircuits and imported analogues are also suitable. Resistors, capacitors and LEDs will suit any type. Capacitor C2, for stable operation of the capacitive sensor when operating in conditions of large temperature fluctuations environment need to be taken with a small TKE.
The sensor is installed under the toilet platform on which it is installed cistern in a place where, in the event of a leak from the tank, water cannot enter. The sensor body is glued to the toilet using double-sided tape.
The antenna sensor of the capacitive sensor is a piece of copper stranded wire 35 cm long insulated with fluoroplastic, glued with transparent tape to the outer wall of the toilet bowl a centimeter below the plane of the glasses. The sensor is clearly visible in the photo.
To adjust the sensitivity of the touch sensor, after installing it on the toilet, change the resistance of the trimming resistor R3 so that the HL2 LED goes out. Next, place your hand on the toilet lid above the location of the sensor, the HL2 LED should light up, if you remove your hand, it should go out. Since the human thigh by mass more hands, then during operation the touch sensor, after such adjustment, will be guaranteed to work.
Design and details of capacitive touch switch
The capacitive touch switch circuit has more details and a housing was needed to accommodate them bigger size, and for aesthetic reasons, the appearance of the case in which the presence sensor was placed was not very suitable for installation in a visible place. The rj-11 wall socket for connecting a telephone attracted attention. It was the right size and looked good. Having removed everything unnecessary from the socket, I placed a printed circuit board for a capacitive touch switch in it.
To secure printed circuit board A short stand was installed at the base of the case and a printed circuit board with touch switch parts was screwed to it using a screw.
The capacitive sensor was made by gluing a sheet of brass to the bottom of the socket cover with Moment glue, having previously cut out a window for the LEDs in them. When closing the lid, the spring (taken from a silicon lighter) comes into contact with the brass sheet and thus ensures electrical contact between the circuit and the sensor.
The capacitive touch switch is mounted on the wall using one self-tapping screw. For this purpose, a hole is provided in the housing. Next, the board and connector are installed and the cover is secured with latches.
Setting up a capacitive switch is practically no different from setting up the presence sensor described above. To configure, you need to apply the supply voltage and adjust the resistor so that the HL2 LED lights up when a hand is brought to the sensor, and goes out when it is removed. Next, you need to activate the touch sensor and move and remove your hand to the switch sensor. The HL2 LED should blink and the red HL3 LED should light up. When you remove your hand, the red LED should remain lit. When you raise your hand again or move your body away from the sensor, the HL3 LED should go out, that is, turn off the water supply in the bidet.
Universal PCB
The capacitive sensors presented above are assembled on printed circuit boards, slightly different from the printed circuit board shown in the photo below. This is due to the combination of both printed circuit boards into one universal one. If you assemble a touch switch, you only need to cut track number 2. If you assemble a touch presence sensor, then track number 1 is removed and not all elements are installed.
The elements necessary for the operation of the touch switch, but interfering with the operation of the presence sensor, R4, C5, R6, C6, HL2 and R4, are not installed. Instead of R4 and C6, wire jumpers are soldered. The chain R4, C5 can be left. It will not affect work.
Below is a drawing of a printed circuit board for knurling using the thermal method of applying tracks to the foil.
It is enough to print the drawing on glossy paper or tracing paper and the template is ready for making a printed circuit board.
Trouble-free operation of capacitive sensors for sensory system water supply control in the bidet has been confirmed in practice over three years of continuous operation. No malfunctions were recorded.
However, I would like to note that the circuit is sensitive to powerful impulse noise. I received an email asking for help setting it up. It turned out that during debugging of the circuit there was a soldering iron with a thyristor temperature controller nearby. After turning off the soldering iron, the circuit started working.
There was another such case. The capacitive sensor was installed in a lamp that was connected to the same outlet as the refrigerator. When it was turned on, the light turned on and when it turned off again. The issue was resolved by connecting the lamp to another outlet.
I received a letter about the successful application of the described capacitive sensor circuit for adjusting the water level in storage tank made of plastic. In the lower and upper parts there was a sensor glued with silicone, which controlled the turning on and off of the electric pump.
What tricks do owners resort to to protect their property! Starting from the simplest padlocks the size of good brick(in the North they even used... wolf traps!) until modern alarm system with sophisticated electronics. Electronic security is often based on the fact that the criminal will somehow give himself away and send information about his appearance. It could be the sound of footsteps - the electronic “ears” will instantly react and give a signal of danger. There are security systems that respond to human radiation, the spectral composition of which differs sharply from the main background. But the criminal does not sleep, trying to become unnoticed while committing his dirty deeds - special camouflage suits and all sorts of ingenious devices appear.
Meanwhile, there is an absolutely reliable protection system. It is tuned to such a physical field of a person, for which nature itself excludes the possibility of any obstacles. This is the gravitational field that every object that has mass has. Gravity is gravitation (attraction), the universal interaction between any types of physical matter ( ordinary substance, any physical fields), this is what Isaac Newton’s third law says.
This principle formed the basis of the device of the famous inventor Sh. Lifshitz. Gravitational forces are negligible. Let's say, the mutual attraction between two bodies located at a distance of one meter from each other and with each mass of one ton is only about 0.006 g. They can only be observed with the help of bulky devices that are used only in planetariums. The device of Sh. Lifshitz is small, compact, extremely simple to manufacture and ingenious, like everything ingenious. Its basis is a transparent vessel glued together from plexiglass. Inside there is a partition that symmetrically divides it to half the height and goes out. Two tubes with a cross section of 1 square meter are mounted on both sides of the partition. mm. On the sides of the vessel there are two short tubes with taps. All connections of the device are sealed.
The vessel is placed on a table or on a fixed platform. A drop of colored liquid is introduced into the small tubes. Both drops should be at the same level. After this, the vessel is filled with water through short tubes to a level at which Bottom part The partition is completely immersed in the liquid, and a layer of air of 2 - 3 mm remains before the lid of the vessel. The taps are closed and the device is ready for use. If a person now approaches one of its ends, part of the liquid, under the influence of gravitational force, will move from one half of the vessel to the other - to the one to which he approached. And since the movement of liquid in the separated parts of the vessel is associated with the movement air gap, then the colored drops in the small tubes will also move. Removing a person from the device will cause the opposite effect - reverse displacement of the droplets. There is a demonstration of the effect of gravity.
If you bring a weight to the device, the drop in the left capillary will rise, and in the right it will fall
Now can you guess where we're going with this? We only need to slightly improve our device so that it automatically gives a signal when a person approaches it. There are many options here. Moving, tinted droplets can block the beam of light and cause the photocell to fire and turn on the siren.
Look at the picture and you will better understand the mechanism of action of such a guard. The device works if it is secured by armored door safe or behind a thick concrete wall- there are no obstacles for gravity. In other words, similar security device the most reliable.
Such a device will automatically sound a signal when a person approaches it.
Today, no one will be surprised by electronic preventive warning devices that vary in purpose and effectiveness, which notify people or turn on a security alarm long before the direct contact of an unwanted guest with a protected boundary (territory). Many of these nodes described in the literature, in my opinion, are interesting, but complicated. In contrast to them, simple electronic circuit non-contact capacitive sensor (Fig. 1), which even a novice radio amateur can assemble. The device has numerous capabilities, one of which - high input sensitivity - is used to warn about the approach of any animate object (for example, a person) to the E1 sensor.
The circuit is based on two elements of the K561TL1 microcircuit connected as inverters. This microcircuit contains four elements of the same type with a 2I-NOT function from a Schmitt trigger with hysteresis (delay) at the input and inversion at the output. Functional designation - the hysteresis loop shows
Rice. 1. Electrical diagram of a non-contact capacitive sensor in such elements inside their designation. The use of K561TL1 in this circuit is justified by the fact that it (and the K561 series of microcircuits, in particular) has very low operating currents, high noise immunity (up to 45% of the supply voltage level), and operates in a wide range of supply voltage (from 3 to 15 V) , has input protection from static electricity potential and short-term excess of input levels and many other advantages that allow it to be widely used in amateur radio designs without requiring any special precautions and protection.
In addition, K561TL1 allows you to connect its independent logic elements in parallel, as buffer elements, as a result of which the power of the output signal increases multiple times. Schmitt triggers are, as a rule, bistable circuits capable of working with slowly increasing input signals, including those with an admixture of noise, while providing steep pulse edges at the output, which can be transmitted to subsequent nodes of the circuit for coupling with other key elements and microcircuits.
The K561TL1 microcircuit (as well as the K561TL2) can allocate a control signal (including digital) for other devices from a fuzzy input pulse. The foreign analogue of K561TL1 is CD4093B.
Limit state close to low logic level. At the output DD1.1 - high level, at the output DD1.2 is low again. Transistor VT1, which acts as a current amplifier, is closed. Piezoelectric capsule HA1 (with internal 3CH generator) is inactive.
An antenna is connected to the E1 sensor - a car telescopic antenna is used as it. When a person is near the antenna, the capacitance between the antenna pin and the floor changes. This causes elements DD1.1, DD1.2 to switch to the opposite state. To switch the node, a person of average height must be (walk) next to the 35 cm long antenna at a distance of up to 1.5 m.
A high voltage level appears at pin 4 of the microcircuit, as a result of which transistor VT1 opens and capsule NA1 sounds.
By selecting the capacitance of capacitor C1, you can change the operating mode of the microcircuit elements. So, when the capacitance C1 is reduced to 82-120 pF, the node works differently. Now sound signal It sounds only as long as input DD1.1 is affected by alternating voltage interference - human touch.
The electrical circuit (Fig. 1) can also be used as the basis for a trigger sensor node. To do this, eliminate the constant resistor R1, the shielded wire, and the sensor is microcircuit contacts 1 and 2.
A shielded wire (cable RK-50, RK-75, shielded wire for signals 34 - all types are suitable) 1-1.5 m long is connected in series with R1, the screen is connected to the common wire. The center (unshielded) wire at the end is connected to the antenna pin.
If the specified recommendations are followed and the types and ratings of elements specified in the diagram are used, the unit generates a sound signal with a frequency of about 1 kHz (depending on the type of HA1 capsule) when a person approaches the antenna pin at a distance of 1.5-1 m. There is no trigger effect. When a person moves away from the antenna, the sound in the HA1 capsule stops.
The experiment was also carried out with animals - a cat and a dog: the node does not react to their approach to the sensor - antenna. The principle of operation in this device is based on changing the capacitance of the sensor-antenna E1 between it and the “ground” (common wire, everything that relates to to the grounding circuit, - in in this case these are the floor and walls of the room). When a person approaches, this capacity changes significantly, which is sufficient to trigger the K561TL1 microcircuit.
Practical use knot is difficult to overestimate. In the original version, the device is mounted next to door frame multi-apartment residential building. Entrance door- metal.
The volume of signal 34 emitted by the HA1 capsule is sufficient to hear it in a closed loggia (it is comparable to the volume of an apartment bell).
The power supply is stabilized with a voltage of 9-15 V, with good filtering of the ripple voltage across the output. Current consumption is negligible in standby mode (several microamps) and increases to 22-28 mA when active work emitter NA1. A transformerless source cannot be used due to the likelihood of damage electric shock. Oxide capacitor C2 acts as an additional power supply filter, its type K50-35 or similar, for an operating voltage not lower than the voltage of the power source.
During operation of the unit, interesting features. Thus, the supply voltage of the node affects its operation. When the supply voltage is increased to 15 V, only an ordinary stranded unshielded electrical copper wire with a cross-section of 1-2 mm and a length of 1 m is used as a sensor-antenna. In this case, no screen or resistor R1 is needed. The electrical copper wire is connected directly to pins 1 and 2 of element DD1.1. The effect is the same.
When the phasing of the power supply plug changes, the node catastrophically loses sensitivity and is only able to work as a sensor (reacts to touching E1). This is true for any value of the power supply voltage in the range of 9-15 V. Obviously, the second purpose of this circuit is an ordinary sensor (or sensor-trigger).
These nuances should be taken into account when repeating the knot. However, when correct connection, described here, turns out to be an important and stable part of the security alarm system, ensuring the safety of the home, warning the owners even before an emergency situation occurs.
The elements are mounted compactly on a fiberglass board.
Housing for a device made of any dielectric (non-conducting) material. To control the power supply, the device can be equipped with an indicator LED connected in parallel with the power source. 
Rice. 2. Photo of the finished device with a car antenna in the form of a capacitive sensor
No adjustment is required if the recommendations are strictly followed. Perhaps, with other options for sensors and antennas, the node will manifest itself in a different quality. If you experiment with the length of the shielding cable, the length and area of the sensor-antenna E1 and changing the supply voltage of the node, you may need to adjust the resistance of the resistor R1 within a wide range from 0.1 to 100 MOhm. To reduce the sensitivity of the unit, increase the capacitance of capacitor C1. If this does not bring results, a constant resistor with a resistance of 5-10 MOhm is connected in parallel with C1.
Non-polar capacitor C1 type KM6. Fixed resistor R2 - MLT-0.25. Resistor R1 type BC-0.5, BC-1. Transistor VT1 is necessary to amplify the signal from the output of element DD1.2. Without this transistor, the HA1 capsule sounds weak. Transistor VT1 can be replaced with KT503, KT940, KT603, KT801 with any letter index -
The HA1 emitter capsule can be replaced with a similar one with a built-in generator 34 and an operating current of no more than 50 mA, for example FMQ-2015B, KRKH-1212V and similar.
Thanks to the use of a capsule with a built-in generator, the unit exhibits an interesting effect - when a person approaches the sensor-antenna E1, the sound of the capsule is monotonous, and when the person moves away (or approaches the person at a distance of more than 1.5 m), the capsule produces a stable, intermittent sound in accordance with with a change in the potential level at the output of element DD1.2.
If a capsule with a built-in interrupt generator 34, for example KPI-4332-12, is used as HA1, the sound will resemble a siren at a relatively large distance of a person from the antenna sensor and an intermittent signal of a stable nature at maximum approach.
Some of the disadvantages of the device can be considered the lack of “friend/foe” selectivity - thus, the node will signal the approach of any person to E1, including the owner of the apartment who went out “to buy a loaf of bread”.
The basis of the operation of the unit is electrical interference and changes in capacitance, which are most useful when operating in large residential areas with a developed network of electrical communications. It is possible that such a device will be useless in the forest, in the field and anywhere where there are no electrical communications of the 220 V lighting network. This is a feature of the device.
By experimenting with this unit and the K561TL1 microcircuit (even when it is turned on normally), you can gain invaluable experience and real, easy to repeat, but original in essence and functional features electronic devices.