Light touch switch circuit diagram. The easiest way to turn a regular screen into a touch screen
The simplest sensor device can be assembled using several available parts. Just three transistors, three resistors and one LED, that's all. You can even assemble the circuit by hanging it, everything will work.
Transistors of any NPN structure: KT315, KT3102 or BC547 or any other. Resistors 0.125-0.25 Watt. LED of any color, but red is better, since its voltage drop is minimal. Power supply is 5 volts, more less is possible and less is also possible.
All components were compactly connected to each other on a miniature printed circuit board, which can be made simply by cutting out the excess copper with a cutter, leaving in this way sharp-angled polygons. Parts used for surface mounting, transistors in sot-26 npn, resistors 0805, jumpers - pieces of wire, instead of them, if you have them, take large 2512 resistors with zero (conditionally) resistance. The touch device works immediately, without setup.
Explanation of how the circuit works
By touching the base of transistor Q3, you open it with crosstalk, as a result of which a current flows through its CE and a 1 MΩ resistor, which opens the next semiconductor Q2, which opens, opens Q3, which already controls the LED, opening through its CE a current flows, from the minus goes to the cathode LED, and it is already connected to the anode. The 220 Ohm resistor here is “current limiting”, excess voltage drops across it, which protects the diode from crystal degradation and complete failure of LED1
Application
Well, the LED lights up when you touch your finger - so what? But the fact is that instead of this LED we install a relay and now we can control almost any load, depending on the characteristics of the relay used. We put a powerful incandescent lamp connected to the network, and relay contacts in the break of this circuit. Now when you press, or rather touch the sensor, the lamp lights up.
You can also organize switching on/off of the load using an optocoupler; if there is no relay, then there will also be galvanic isolation. This beautiful thing consists of an LED and a phototransistor, when the first one shines, it opens the transistor and current can flow through its CE. We include the necessary outputs of the optocoupler in the sensor circuit instead of LED1, and the remaining two in the gap between the power source and any load. This part can be removed from phone chargers. Take the PC-17L1 for example.
Just below you see an addition to the main circuit, which shows how to connect an optocoupler to the sensor circuit; one transistor has also been added, this is necessary so that you can connect a heavy load, and not just 20 mA LEDs.
Instead of a relay and an optocoupler, it is also possible to use two NPN transistors. That's what I did, you can see the diagram. It works like this: Q5 should always be open through a 10 kOhm resistor, but through the CE of open Q4, a “minus” is sent to the base of Q5 and because of this it is closed. When you touch the sensor, the minus goes through the open Q1 to the Q4 base and closes it, now nothing prevents Q5 from remaining open - the load is working, and in my case, the powerful 1 Watt LED shines brightly.
This is what it looks like when assembled.
The sensor does not have a fixation; when you touch it, it lights up, when you release it, it doesn’t light up. If you want to make a fix, just add a trigger to the circuit, for example, on a KM555TM2 chip or any other (you can even implement this on a 555 timer). With the addition of a trigger system, when you touch the sensor, the load will be turned on until the next touch occurs or the power to the circuit disappears.
In practice, this can be used to quickly turn on and off the lighting in a room. Very convenient, touch a small sensitive area and the room is illuminated, a second touch will turn off the light. A small amount of energy will be lost, but this can be neglected.
Comments
The scheme works, but due to its simplicity it is far from ideal. If the sensor is large, then the circuit may be triggered even when you have not yet touched it; also, if you comb your hair near the sensor with your hand, the LED may also light up. The way out of this situation is simple - a miniature touch sensor.
As already mentioned, the opening of Q3 occurs due to interference, you can see this in the video, the LED does not shine constantly, but winks with a high frequency, but this is clearly noticeable when shooting.
The brightness of the working diode is not great if you only touch the base of the third transistor, but as soon as you touch the power plus, your body will act as a resistor and transistor Q3 will go into saturation. But in this situation, for some, the meaning of the sensor will be lost.
This diagram is very simple and is intended only to understand the principle of operation.
Quite often it is necessary to replace conventional switches for electrical appliances with new ones due to their rapid wear. They were replaced by more reliable touch switches (TS). The principle of their operation is as simple as possible. The devices can be made by hand. The photo below shows a switch with a sensor located on top and an indicator LED on the bottom.
Appearance of the touch switch
To turn on the light, a light touch on the sensitive element is enough. Touch switches are usually used to control lights, electric curtain rods and other low-power devices.
Advantages of SV
- Convenient compared to a key switch, which does not always switch immediately. The devices are completely silent and there is no need to make an effort to turn them on.
- You can choose stylish models that will decorate your premises.
- Galvanic isolation of the circuit makes the device completely safe. The sensor can be touched with wet hands, the switch is sealed.
- No mechanisms that can break. The entire circuit consists of electronic elements.
- Possibility of combining with remote light control, as well as creating several switching channels in one device.
- Possibility of making it yourself.
Operating principle
Any touch switch is functionally divided into three parts:
- a sensitive element (sensor) that responds to the touch or approach of fingers;
- a semiconductor circuit that amplifies a weak electrical signal from the sensor;
- a switch (relay or thyristor) that turns the load on and off.
The figure shows a circuit of a touch switch with a supply voltage of up to 16 V. It is a simple semiconductor cascade amplifier. Used to switch on small loads. There is enough static electricity in the human body to open the first transistor of the cascade if you touch the bare conductor connected to the base with your finger.
Circuit of a simple touch switch from a three-stage amplifier
An LED is connected as a load at the output of the third stage, which serves to demonstrate the operation of the circuit. Instead, a relay is installed in the switch, for which a more powerful transistor can be selected. Copper foil can serve as a sensor.
When you touch the sensor, the first stage opens, then the signal is amplified in the next two and the output becomes 6 V. It is enough to trigger the relay, which turns on the lamp with its contact (not shown in the diagram).
Scheme
The figure shows a diagram of a two-stage touch switch that you can make yourself.
Switch circuit with two transistors
When touching sensor E1, voltage from the human body is supplied to the amplifier through capacitor C1. Relay K1 is connected as a load, which is activated at the next touch, turning on or off its power contacts for powering the lamp. Diode VD1 is designed to protect transistor VT2 from voltage surges, and capacitor C2 smoothes out ripples.
The relay is selected for an operating current of 15-20 mA (type RES55A or RES55B). The value of resistor R1 may need to be changed for the relay to work reliably. First, a 50 Ohm variable resistor is connected instead of it and adjusted until the relay from the sensor works. Then the resistance value is measured and a constant resistor with the appropriate value is found.
The sensor used is foil-coated textolite, copper plate or metal with an anti-corrosion coating. It is easy to make it yourself. If the sensor is installed at a distance from the board, the supply wire should be shielded.
The voltage source is a 9 V battery or a home-made mains power supply. A charger may be fine.
It is better to assemble the switch circuit on a board, but you can also solder it with wires, since there are few parts. To connect them together, wires 2-3 cm long are used. To connect to the contact of the sensor and relay, the length of the wires will be no more than 10 cm.
When soldering, it is important not to overheat the transistors and the 0.22 uF capacitor.
Transformerless power supply from a 220 V AC network does not require a separate source. The triac device is quite sensitive and works reliably. In the diagram below there is no galvanic isolation from the lighting network, but the sensor is protected from high voltage by resistors R1 and R2 with a total resistance of 12 mOhm, as well as field-effect transistor VT1 with a high resistance of the drain-source-gate junction. The sensitivity of the circuit is adjusted by changing resistance R2.
In such circuits, when they are energized, touch is allowed only to the E1 sensor.
Scheme of a touch electronic switch on a triac
The trigger is built on an integrated circuit K561TM2 (DD1). From its output 1, the signal goes to the base of the transistor current amplifier VT2, the emitter of which is connected to the control terminal of the triac VS1. As soon as a voltage of 3 V appears on it, the triac opens and turns on the light source. The next time you touch the sensor, the trigger changes state and an opposite signal appears at output 1, turning off the EL1 lamp.
The load power for this circuit is no more than 60 V. If it needs to be increased, the triac is installed on the radiator.
There are circuits with a dimming function. When you briefly touch the sensor, the lamp will light up and go out. If you hold your hand on the sensing element, the brightness will increase and then decrease. A similar device is convenient to use for a table lamp at your desk. You can set a specific lighting level by removing your hand from the switch. The figure shows a diagram of the touch controller.
Touch dimmer circuit
The signal is supplied from the sensitive element to the K145AP2 microcircuit, and it controls the triac VS1 through the transistor VT1. Power is supplied from a 220 V network. The HL1 LED is a voltage indicator and illuminates the sensor in the dark.
Digression about delivery and track
A Chinese guy gave me a strange track UA******YP. At first I thought that the goods were sent to Ukraine by mistake, which I wrote to the seller about.
The seller assured that everything was fine with the shipment. That they use new logistics to speed up delivery and that these tracks can be tracked by address
or
But these sites said nothing about my track :(
Resoldering triacs is a matter of minutes 
I had to bend the electrolytic capacitors a little differently, since one was touching the triac housing. But the BT137, alas, is not isolated.
I turn it on - everything works like a clock. As a result, I get a touch switch “1-WAY 5A” according to Chinese gradation;)))
In fact, a triac in a TO-220 housing without a radiator can switch 150-200W.
But who’s stopping you from putting a triac on the radiator? For example, a 25cm2 radiator allows you to switch 800W, if the full load of this triac is 8 standard (not Chinese amperes)?
And in order to ensure that there is no high voltage on the radiator, it is attached to the triac with the following things - plastic insulators for the screw and silicone gaskets:
which are sold for pennies, 50-100 pieces 
- $1.42/100
- $0.99/100
Well, or you can do it the old fashioned way using mica plates.
So the switches arrived, were successfully modernized and put into operation.
The assets still have 5 used low-power MAC97 triacs and a pair of “3-WAY” switches for Chinese 3A.
I spent a long time studying circuit boards for switches.
Unfortunately, I didn’t find any jumpers that set the “1-WAY/3-WAY” operating mode. Apparently, different “black blot” microcircuits or their firmware are used, if it is a PLC.
Let's sum it up
Advantages:
- Works flawlessly (if it doesn’t immediately burn out in power)
- Low price
- Small dimensions
- Easy connection
- Can be upgraded to increase desired power
Flaws:
- Maximum switching current is significantly less than stated
- Very flimsy wires
The sensor does not respond to the cat, but he is extremely dissatisfied with the experiment 
When using household light switches in residential apartments and offices, they often fail due to the presence of moving rubbing parts. Recently, they are increasingly being replaced with more reliable and durable touch switches. The design and operating principle of these devices are very simple, which allows you to make a touch switch with your own hands. The figure below shows a device equipped with a built-in sensor.
In order to switch the electronic switch into an active state, it is enough to lightly touch the sensing element, which eliminates the need for mechanical contact with the actuator module. These devices are most often used when it is necessary to control the switching on of lights, electrically operated curtains and other mechanisms with not very high power consumption.
Advantages
The advantages of touch switching devices include:
- Ease of control of the switching circuit (in comparison with a frequently stuck key switch);
- Absolutely silent operation of the executive module, which is built into the switch;
- Safety of operation of the product located in the housing, power to which is supplied through galvanic isolation;
- And finally, a modern aesthetic look that decorates the interiors of any room.
Note! If necessary, the sealed touch surface can be touched with wet hands, which is not entirely safe for conventional devices with a key.
In addition, such devices are easily compatible with remote control systems that allow the possibility of installing several control channels. These products are also good because they can be easily made with your own hands.
Device and principle of operation
Any simple touch switch contains the following three components:
- A special sensitive element that is triggered by the touch of a finger or its approach to the surface;
- Scheme of a touch-sensitive light switch based on semiconductor elements that provide amplification of weak signals coming from the sensor;
- An executive or switching unit made of transistors and relays (with its help the load is controlled).
Let's consider the principle of operation using the example of a simple electronic device operating from a supply voltage of 16 Volts. The figure below shows a diagram of a touch switch of this type.
The figure shows that the electronic part is made in the form of a cascade amplifier that processes a weak signal coming from the sensor and increases its amplitude to the required level. This version of the switch can be used for switching small current loads.
The first stage of the amplifier is configured in such a way that the static electricity present on the human body is quite enough to open the input transistor VT1 when you touch its base with a finger. The total number of stages in this circuit is three, which makes it possible to achieve the required output gain.
To finalize this circuit, you will need to include a load relay (instead of a 220 Ohm resistor) in the collector circuit of the output transistor. When the relay element is triggered, its contacts supply voltage from the household network to the light bulb circuit, after which it lights up.
When touched again, the same potential of the human body leads to the closure of the transistor and the loss of voltage on the relay winding. Its executive contacts turn off the circuit that powers the lighting line.
Important! The type of e/m relay is selected in such a way that with the help of its contacts it is possible to switch significant currents.
Practical schemes
Adjustable switch
In addition to the simplest switching device already discussed earlier, there are sensors in a slightly different design.
Some samples of such electronic devices can be made in the form of a switch with a lighting control function, for example. The circuit of such a device contains another additional unit responsible for controlling the current strength in the executive circuit (it is usually performed using thyristors).
When you lightly touch the sensor, the light bulb controlled by it first lights up immediately and then goes out. But if you hold your finger on the area with the sensitive element a little longer, the brightness of the glow first increases, and after some time begins to decrease.
Such switches are very convenient if you use them for a table lamp, for example. With their help, it is possible to set the desired brightness by removing your finger from the key at the right moment (the diagram of the device with a light controller is shown below).
The electronics of the device works in this way:
- First, a weak signal generated on the sensitive element is supplied to the input of the K145AP2 microcircuit, which amplifies it to the required value, and then through transistor VT1 it is supplied to the control electrode of triac VS1;
- Depending on the duration of the on state of the transistor, the opening time of the output control element will change;
- When you hold your finger on the sensor for a long time, the current strength in the supply circuit will increase, and along with it, the illumination in the room will begin to increase;
- To lower it to zero (turn off the light), your finger should be kept on the sensitive surface even after reaching maximum illumination.
Additional explanation. A triac element works as follows: when it is opened by a switch, the average value of the current through the junction increases, and when closed, on the contrary, it decreases.
The supply voltage is supplied to this circuit from a 220 Volt household network. The HL1 LED located on the front of the key signals the presence of power and at the same time illuminates the device at night. The zener diode installed in the output circuits is selected in such a way that the voltage across capacitor C5 is established within the range of 14 to 15 Volts. At lower values of the control parameter, the lamp may begin to flicker.
When making the switch's sensitive element yourself, ordinary copper foil can be used as a touch pad.
Simple 2-transistor circuit
The simplest version of the devices under consideration is a circuit with two transistors (figure below), which works as follows.
In the event of touching the sensitive element E1, the potential from the human body through the isolation capacitor C1 is supplied to the amplifier. The coil of the electromagnetic relay K1 is used as its load element, which is triggered after the next touch of the sensor.
In this case, the actuating contacts supply power to the lighting circuit, due to which the light bulb turns on. When you touch the pad with the sensor a second time, the control circuit turns off the relay, and the light bulb immediately turns off.
In conclusion, we note that making such a switch with your own hands is not at all difficult. To do this, just read the material given here and try to follow all the recommendations therein.
Video
The idea of controlling lighting fixtures using touch switches is not new; similar switches or light switches were produced back in the last century. But the dimensions of such devices were significantly larger than standard ones, which caused problems during installation. It is also worth noting that the cost of the first touch switches was quite high; naturally, this did not contribute to their popularity. With the development of technology, the situation has changed radically, and today capacitive, infrared and remote switches are in stable demand.
Design and operating principle
Despite the variety of models of touch communicators, most of them have a standard design consisting of the following elements:
- Housing made of heat-resistant plastic (see A in Fig. 1). The dimensions of the structure allow installation in a typical mounting location of a conventional switch.
- Electronic unit (B), it includes a power adapter and a semiconductor switch control circuit.
- Board with capacitive sensors (C).
- The front panel (D), as a rule, is made of quartz glass; budget models may use other materials.
Now we will tell you how such devices work. The electronic unit monitors the state of the sensor. When you touch a certain place on the front panel of the switch with your hand (it is marked accordingly), the capacitance of the sensor changes. The electronic unit detects this and changes the state of the contactless semiconductor switch, which opens or closes the electrical circuit.
Scope of application
Initially, this type of switch was planned to be used to turn on/off lighting, but the design turned out to be so successful that the scope of its application has expanded significantly. Today, most modern household appliances have touch controls; examples include kitchen stoves, hoods, microwaves, etc.
The only limitation on connecting to touch switches is the power of the equipment; its permissible parameters are indicated in the device passport.
Additional functionality
Modern technical base has made it possible to install microcontrollers in the electronic control unit of a touch switch, which has significantly expanded the functionality of switches and allowed them to fit into the concept of a smart home. Such switches can be controlled by voice, infrared or radio remote control, smartphone via WI-FI or a programmable timer.
The touch switch can be connected to the smart home system and controlled using a mobile phone Touch switches can be used in conjunction with sensors that respond to motion or light levels. In the first case, such devices turn on a lamp, table lamp or other lighting fixtures when someone enters a room, such as a bathroom. With the second implementation option, the light will turn on at a low light level.
Sesoo Triple Touch Switch and Motion Sensors Some manufacturers, for example, Livolо, produce touch switches with a dimmer function or that control combined sockets, to which almost any household appliance can be connected.
Livolo touch switch with socket block Advantages of capacitive switches
Speaking about the advantages of this type of switches, the following qualities should be noted:
Now briefly about the shortcomings. First of all, it is necessary to note the difference in cost with conventional mechanical switches, but it has become significantly less than 10-20 years ago. The price of inexpensive Chinese touchscreen models today is much cheaper than mechanical switches from well-known brands, such as GTS or Electronics.
Sometimes LED lamps connected to touch switches flicker. This may be due to both the low quality of the lighting sources themselves and the low-cost switch models. The problem can be resolved in two ways:
- Use products from well-known brands (Jazzway, Panasonic, Sapphire, Funry, LightaLight, Tronic, Sesso, etc.).
- Connect a 0.1 uF 630 V capacitor in parallel with the LED lamp.
Connection
The installation of touch switches is practically no different from the installation of conventional built-in and surface-mounted mechanical switches. You can read more about this process on the pages of our website. Let us remind you how to do this using the example of the kg020gs model from the manufacturer FD Electronics.
Connection algorithm:
Figure 8. Second and third connection stages Some manufacturers, for example, Livolo, produce pass-through switches for 220 V (their connection diagram is shown in Fig. 9). With their help, you can control lighting from several places.
Figure 9. A clear example of how to connect several pass-through touch contact panels Each of these switches controls the lighting in the room from different locations. The concept involves using a main switch and one auxiliary (or more). On the main devices there are three terminals, the phase is connected to one, the zero is connected to the other, and the control conductor is connected to the third. Accordingly, such contacts are marked as: L – phase, N – zero and Com – control wire. Assistive devices
Secondary switches are connected through two terminals: N – zero and Com – control contact. Labeling may vary from manufacturer to manufacturer, so it makes sense to study the instructions. An example is the connection diagram for the electronic dimmer et0802193e, or its analogue tt6061a, which can be controlled with a light touch of your hand.
Selecting a touch light switch
Before purchasing a device, you need to determine its functionality. To do this, the following criteria must be taken into account:
- Power of connected equipment and its connection diagram.
- Execution corresponding to the type of wiring.
- Operating conditions (if installation is planned in the bathroom, then a device with moisture protection is selected).
- Possibility of remote control (remote control or smartphone).
- Compliance of the design with the interior of the room, etc.
Having decided on the main tasks, you can begin to select a manufacturer. Naturally, you should give preference to well-known brands whose products are reliable. But at the same time, it is necessary to take into account the presence in the model range of switches of devices with the necessary functions. For example, Delumo has devices controlled by a radio remote control, and Sonoff specializes in Wi-Fi devices, Capsens Domuns Line lamps are “tailored” only for their touch switches, etc. There can be many nuances, so we recommend that you study the various options in detail.
Based on practical experience, in addition to well-known brands such as Legrand, we can recommend Vento Electric, Wemmon, Fanri, Merten, CGSS, Steu, Schneider, Ariston, etc.
MakeGood Classic wireless touch switch with remote control and backlight We recommend monitoring reviews online, where ratings of the best manufacturers are published. Selection criteria are made both by the model range of manufacturers, taking into account functionality and cost, and by other indicators.
Refinement of standard devices
Many people are not happy that the touch zone on the panel is quite small, and to record a signal you need to touch it in the indicated place. Let's give an example of how you can increase the area of indirect surface contact.
You should take the wire and carefully solder it to the place where the signal is supplied from the sensor on the touch board (for this you need to study the circuit diagram of the device). The connected wire is laid around the perimeter of the housing. As a result, such a frame will make it possible to trigger the sensor when touching the front panel without amplifying the signal level.
It should be noted that such an improvement will void the manufacturer's warranty.
DIY touch switch
For those who like to work with a soldering iron, we can recommend several circuits of touch switches that will be easy to assemble with your own hands. Let's start with a simple field-effect transistor circuit, this is exactly the principle that was laid down in the first sensor devices.
Designations:
- Resistances: R1 - 10..15 kOhm (must be selected for sensor response), R2 - 3...5 MOhm.
- Capacitors: C1 – 1000 pF (suppresses false triggering), C2 – 33.0 µF x 50 volts, C3 – 470 µF x 50 V.
- Transistor VT1 – KP 501A.
- Relay K1 can be used of any type whose operating current does not exceed 150.0 mA.
The circuit is powered from a source with a voltage of 12…24 V.
Now let's look at an option based on the NE555 asynchronous RS trigger. The device diagram is shown below.
Designations:
- Resistors: R1 – 1.0 MOhm, R2 – 1.0 MOhm, R3 – 1.0 kOhm.
- Capacitors: C1 and C2 – 15 nF, C3 – 10 nF, C4 – 0.1 µF, C5 – 100.0 µF x 25 V.
- Diodes: D1-D2 – 1N4001, D3 – standard indicator LED.
- Microcircuit - NE555,
- The relay is the same as in the previous electrical circuit.
The above diagram does not need to be configured.
Concluding the topic of homemade sensor devices, we should mention the Ardunio system. On this platform, you can assemble a switching device that can be easily integrated into a Smart Home. In addition, such a device can be easily configured to operate independently, in accordance with a given program.
In addition, the system allows you to create several profiles for specific tasks. However, this will require programming skills. You can get more detailed information about the Ardunio platform on our website.
Note that in the above circuits, a power source with a voltage of 12-24 V is required to power the control circuit. For this purpose, it is best to use switching power supplies. The electronic balance of LED and energy-saving lamps is ideal as such. Detailed information on this topic can also be found on our website.
