A capacitive sensor is one of the types of non-contact sensors, the operating principle of which is based on a change in the dielectric constant of the medium between two capacitor plates. One covering serves touch sensor circuits in the form of a metal plate or wire, and the second is an electrically conductive substance, such as metal, water or the human body.
When developing a system automatic switching on supply of water to the toilet for a bidet, it became necessary to use a capacitive presence sensor and switch with high reliability, resistance to change 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 touch presence sensor circuit is a master rectangular pulse generator, made according to the classical 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 the D1.2 chip rectangular shape through resistor R2 it goes 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 microcircuit D1.3 with a slight change in the slope of the pulse front due to 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 a metal object closer to the antenna (touch sensor), 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 DD1.4 input. 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 key transistor for turning on the 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 would not interfere with sanitization 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 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 parts and a larger housing was required to accommodate them, and for aesthetic reasons, the appearance of the housing 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 flint 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 set it up, 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 the hand is removed, the red LED should remain illuminated. 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.
The trouble-free operation of capacitive sensors for the touch control system for water supply in a bidet has been confirmed in practice over three years of continuous operation. No malfunctions were recorded.
However, I want 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.
Distance and touch sensors
Ultrasonic sensor
The ultrasonic sensor is one of two sensors that replace the robot's vision. The ultrasonic sensor allows the robot to see and detect objects. It can also be used to enable a robot to avoid obstacles, estimate and measure distance, and capture the movement of an object.
Ultrasonic sensor readings are measured in centimeters and inches. It can measure distances from 0 to 255 centimeters with an accuracy of +/-3 cm. The ultrasonic sensor works on the same principle as a bat locator: it measures distance by calculating the time it took for a sound wave to return after reflecting off an object, similar to echo.
Large objects with hard surfaces are best detected. Objects from soft materials(fabric) or round (ball), as well as too thin, small, etc., can create certain difficulties for the sensor when working.
Please remember that two or more ultrasonic sensors operating in the same room may interfere and reduce the accuracy of the results.
Examples of the use of ultrasonic distance sensors include use in cars for warning signals to the driver or automatic control based on signals from sensors that identify dangerous situations, combined into network connections, with a human-machine interface (HMI).
Fig.1
The ultrasonic principle of obstacle detection is based on the echo principle. The sensor consists of two transducers: one transducer emits ultrasonic waves, and the reflected waves are detected by one or more other transducers. The same transducer that transmits ultrasonic waves can also be used to detect the reflected wave. The main purpose of the sensors is to detect the presence or absence of an obstacle, but this principle (time of flight) also allows the distance to the object to be calculated from the time of return of the echo at a known speed of sound propagation.
Ultrasound is nothing more than vibration at a frequency > 20 kHz. Most commercially available converters operate at frequencies in the 40-250 kHz range.
Variations in the acoustic parameters of sensors, the environment and different targets significantly affect the performance of devices.
In an ultrasonic sensor, the transducer generates a short pulse that is sent to the target and returned back
It is important that the speed of sound is a function of the composition and temperature of the medium (air) and affects the accuracy and resolution of the sensor. The accuracy of distance measurements is directly proportional to the accuracy of the speed of sound used in the calculations, and varies in real conditions from 345 m/s at room temperature up to more than 380 m/s at a temperature of about 70 °C. Sound wavelength
is a function of ultrasound speed c and is interrelated with its frequency ѓ, therefore these parameters (wavelength and frequency) also affect resolution and accuracy, as well as minimum size targets and the range of distances measured by the sensor.
Sound attenuation is a function of frequency and humidity, which affects the maximum distance detected by the sensor. Longer waves (lower frequency) have less attenuation. At frequencies above 125 kHz, maximum attenuation occurs at a relative humidity of 100%, at frequencies of 40 kHz - already at a humidity of 50%. Since the sensor must operate at any humidity level, the calculations use the maximum attenuation for each frequency.
Background noise is a function of frequency and decreases as frequency increases, also affecting the maximum detectable distance and minimum target size. Resolution and accuracy are higher at higher frequencies, while range is higher with longer wavelengths.
Touch sensor
A touch sensor is a button that has two possible states - pressed and released. Programmatically, the sensor recognizes another state: Touch.
You can see the reaction of the touch sensor on the display screen in View mode. When the sensor button is not pressed, 0 appears on the display, and when pressed, 1 appears.
By adding a touch sensor to the robot's design (for example, in the form of a bumper), you can make the robot change its behavior when the sensor is activated.
The touch sensor is one of the senses of touch for robots, which makes it necessary where the robot's reaction to objects is required.
The touch sensor allows the robot to touch.
The pressure sensor can determine the moment something is pressed on it, as well as the moment it is released.
The touch sensor is shown in Fig. 2.
Fig.2 Touch sensor
Reference instruments and additional equipment used
Micrometer
To measure the idle speed of the touch sensor, you need a micrometer (or dial indicator) ICH-25, which will measure the distance passed by the sensor until the moment of operation.
ICh-25 is designed for measuring linear dimensions using absolute and relative methods, determining the magnitude of deviations from a given geometric shape and the relative position of surfaces.
Figure 3 shows several types of indicators.
Fig.3.
Parameters of micrometer ICH 25:
Measuring range 0-25 mm.
The division value is 0.01 mm.
Dimensions 159x85x51 mm.
Page 1
Touch sensors are simply used to detect that an object has made contact. A simple microswitch can serve as a touch sensor. Mechanical stress sensors are used to measure the amount of force generated at the point of contact. Typically, strain gauges are used as sensors that measure forces.
In lathes, touch sensors are used to monitor the dimensions of the workpiece, the machined part, and the cutting edge of the tool. Issues of diagnosing robots (anthropomorphic and portal robots built into lathe, and external ones, working in a cylindrical coordinate system) are discussed in Chap.
To measure wear using direct methods, touch sensors are used, which record either dimensional wear or, when moving, wear along the back surface. The design of the sensor is shown in Fig. 4.8, a. Housing 4 is fixed to the moving unit / machine. An alternating magnetic field is created in the electromagnet winding, causing the tip to oscillate. When the tip touches the block, its vibrations are disrupted, which is recorded by an electronic system 8 with an amplifier 7, and the coordinates correspond to the measured size. The sensor is protected from chips. It is used on CNC machines and in GPS not only to measure wear, but also to determine the actual coordinates of the tip of the tool blade for the purpose of automatically adjusting control programs.
The operating principle of a wire tactile sensor (touch sensor) is shown in Fig. 5.26. The robot automatically uses the coordinates of two base points A and B, determined by a tactile sensor at the corner joint, and according to an adjusted program, finds the required welding start point (point C), if the deviation of the butt joint from the original position is caused by its parallel displacement. If the displacement of the butt joint from its original position is caused by its parallel displacement with a turn relative to the welding point, then in order to adjust the robot positioning program of the torch to the starting welding point, it is necessary to determine the coordinates of at least three base points on the joint elements with a sensor.
Zero heads are usually designed on the basis of touch sensors, of which electrical, radio and vibration contact sensors are widely used. These heads, also called touch heads, are divided into two classes: with variable and fixed zero position of the measuring tip.
Let's consider the features of the devices mentioned above when using them as a touch sensor in the specific conditions of a mercury electrolysis workshop.
Sensing the grippers and other executive bodies of the manipulator is performed by gripping force sensors 6 and touch sensors 7 during the interaction of the PR with the external environment.
The welding part of the PR includes: welding rectifier; welding torch; mounting brackets; welding wire feed mechanism; workpiece touch sensor for welding; touch sensor control device; required number of cables; a cylinder with inert gas, a reducer with a flow meter and a gas heater; hoses and sleeves.
A capacitive sensor is one of the types of non-contact sensors, the operating principle of which is based on a change in the dielectric constant of the medium between two capacitor plates. 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. I couldn’t find a ready-made scheme 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, security alarm systems, determine water levels 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 touch presence sensor circuit is a master rectangular pulse generator, made according to the classical 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 chip with a slight change in the slope of the pulse front due to the installed sensor, which is a piece of wire or a 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 a metal object closer to the antenna (touch sensor), 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 DD1.4 input. 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 key transistor for turning on the 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 fluctuations in ambient temperature, must be taken with a small TKE.
A sensor is installed under the toilet platform, on which the flush cistern is installed in a place where, in the event of a leak from the cistern, 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 is larger in mass than the hand, 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 parts and a larger housing was required to accommodate them, and for aesthetic reasons, the appearance of the housing 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 the 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 flint 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 set it up, 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 the hand is removed, the red LED should remain illuminated. 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.
The trouble-free operation of capacitive sensors for the touch control system for water supply in a bidet has been confirmed in practice over three years of continuous operation. No malfunctions were recorded.
However, I want 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 use of the described capacitive sensor circuit to regulate the water level in a plastic storage tank. In the lower and upper parts there was a sensor glued with silicone, which controlled the turning on and off of the electric pump.
The circuit proposed for repetition is an amplifier that is highly sensitive to the electromagnetic field created by external devices. When the input contact of the circuit is connected to the antenna, the LED signals the presence of electromagnetic field radiation and interference from electrical equipment. The LED will also indicate the fact of touching the contact, since the role of the antenna is in in this case performed by the human body. Hence the name - touch sensor. Another name for the circuit is active antenna.
Schematic diagram touch sensor is shown in Figure 1.
The circuit resembles a transistor oscillator n-p-n structures. One of the terminals of winding L1 is connected directly to the input pin X1. The polarity of the VD1 LED does not matter. Resistor R2 limits the current through the LED and, thereby, determines the brightness of its glow when the sensor is triggered.
The touch sensor is assembled on breadboard size 40 × 40 mm. Appearance design is shown in Figure 2.
 |
|
| Figure 2. | Appearance of the touch sensor. |
Windings L1 and L2 are located on a common frame with two winding sections and a tuning ferrite core. The outer diameter of the frame is 10 mm, the length of the core is 23 mm, the thread diameter at the base of the core is 6 mm. In the design shown in Figure 2, L1 is wound on the top section, L2 on the bottom. Each coil contains 100 turns of PEL 0.2 wire. The windings are included according to. Using a screwdriver, the core is screwed into the frame. LED VD1 - any of the AL307 series. A grounding petal is used as X1. Touching it causes the LED to light up.
VD1 can be connected in parallel measuring device, for example, a multimeter in voltage measurement mode, which will allow you to evaluate the level of field strength. In this case, the external antenna can be a piece of mounting wire several centimeters long. Setting up the circuit will come down to choosing the length of the antenna and finding the position of the core at which the voltage on the LED is maximum.
The circuit is not picky about the choice of element base. For example, in the original version of the circuit, a KT815G transistor was used, the resistance of resistor R1 was 100 kOhm. Two coils on a rod ferrite core of a long-wave magnetic antenna from a radio receiver were used as L1 and L2. The coils could be moved along the core. When moving the coils, phenomena were observed that did not contradict the law of electromagnetic induction, in contrast to the scheme proposed in. When the coils were significantly removed from each other and without a ferrite core, the circuit stopped working.
The circuit can find practical application not only in the design of field strength meters, but also in automation and signaling devices. The touch sensor can be connected to the microcontroller. To do this, you should perform an analog-to-digital voltage conversion on the VD1 LED, possibly using the resources of the microcontroller itself, if it contains a built-in ADC.
In conclusion, it should be noted that there are many touch sensor circuits based on field-effect transistors and not containing inductive elements. They may work more efficiently in many cases, but the design shown in this article is an example of the original technical solution and is aimed at beginner radio amateurs.
Literature
- Brovin V.I. The phenomenon of transfer of energy of inductances through the magnetic moments of a substance located in the surrounding space, and its application. - M.: MetaSintez, 2003 - 20 p.
- Krylov K. S., Lee Jaeho, Kim Young Jin, Kim Seunghwan, Lee Sang-Ha. Patent for invention No. 2395876. Active magnetic antenna with ferrite core.
