DIY electronics invention at home. Useful and simple electronic devices and DIY projects

Chapter electronic homemade products will be a good helper for you if you decide to become a self-taught electrician. Surely after a short period of time you will want to make some useful electrical appliance for your home, car or cottage with your own hands.

At the same time, homemade products can be useful not only in everyday life, but also made for sale, for example, homemade Charger for battery.

Here you will find not only useful diagrams, but also electronic tricks and notes. Interesting electronic devices and circuits for them. From which you can make useful homemade products with your own hands.

Many electrical devices You can repair or make new ones yourself. For this home, there will always be something that can be converted to perform new functions: an old electronic watch, a children's car, an out-of-use computer and much more.

Useful crafts can always be repaired or remade.

Electronic homemade products are made with your own hands at home, this can be homemade machine or a small radio bug. All inventions involve electricity, so don't forget to follow safety precautions!

Every modern home uses a variety of lighting devices. However, the most basic of them is considered to be a chandelier, which has a special elegance and beauty. In fact, a quality ceiling light has many distinctive qualities. Distinctive qualities ceiling lamps. Firstly, as we said earlier, similar devices always have an impeccable appearance. And this is not at all surprising, because ultra-modern devices...

Making electronic homemade products with your own hands gained popularity in the last century, when semiconductor devices appeared. With their help, it was quite easy to assemble devices needed for everyday life from old equipment. Today, repair and assembly of equipment for the home or cottage, for a car or garage can also be solved at home.

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Homemade devices for home and garden

Electrical homemade products for home and garden that use the power of electricity can be made by every electrician. Most devices are created using factory components and require only school knowledge of electricity.

Electric kebab maker

The electric kebab maker can be either horizontal or vertical. Stores usually sell vertical ones, and they do their job well after some modification.

To create a horizontal kebab maker you will need a heating element and a frame resembling a barbecue. The heating element can be made from a ceramic tube and a nichrome spiral wound around it. The tube is secured through an insulating material in a metal casing. Drawings will be required to assemble the case.

Barbecue grill

An equally interesting idea is a kebab grill with an electric drive for rotating skewers. By adding an electric motor to a regular barbecue, you can get an excellent device that will cook barbecue in autonomous mode. To organize the skewer drive, you can use a motor from the wipers, from washing machine or any other 12 Volt. Using a system of pulleys and a belt or gear drive, the rotation of the shaft is transmitted to the skewers, and the meat is slowly turned over the coals.

Homemade WI-FI antenna

This antenna will improve the reception quality and Wi-Fi speed in your home. According to reviews, after connecting it, the signal level rises from 5 to 27 Mbit.

For production you need:

• a small metal sieve or colander;
• Wi-Fi adapter (USB);
• USB cable;
• drill;
• epoxy resin;
• camera tripod;
• plastic clamps.

Manufacturing process:

1. We drill a small hole (14 mm) in the center of the sieve and insert a metal pin into it to secure the adapter.
2. We insert the connector from the USB cable into the prepared hole and secure it with epoxy resin. The USB connector after gluing must be strictly perpendicular to the plane of the sieve, then the device will work more efficiently.
3. Then, using two zip ties, “ears” are made through which the cable is attached.
4. We fix the product on a camera tripod. We drill a hole with a diameter of 12 mm in the antenna and tighten it with a nut.

Necessary materials Insert the pin into the drilled hole Glue the USB cable Securing the cable Tripod Installing the antenna using a tripod

Electrical homemade products for the garage

Let's look at a few projects useful homemade products for the garage.

Homemade chandelier

If you have poor lighting in your garage, then a makeshift chandelier will be very useful. To make a bifurcating chuck, you will need a pair of angular chucks, which are sold at a regular hardware store.

Sequencing:

1. We remove the wires from the sockets and fasten them with a plastic tie. We get a socket for two lamps. All that remains is to connect them to the electrical network.
2. To do this we use the base from fluorescent lamp. Carefully break out the lamp, then solder the wires from our design to the contacts of the base.
3. We insulate them well and attach the base on top of the cartridges.

The use of ordinary light bulbs in this design is undesirable - the sockets may melt from heating.

LED device

Another lighting option could be a homemade LED lighting device.

To make it you will need:

• old fluorescent lamp;
• LED Strip Light;
• connecting wires.

The manufacturing sequence is as follows:

1. An LED strip is glued to the lamp body in one or several rows.
2. The connecting wires are connected and brought to the lamp switch.
3. The assembled device is tested.

Spot welding machine

A necessary device in the garage will be homemade apparatus For spot welding, the basis of which is a transformer from an old microwave oven. Prerequisite— the transformer must be working in order not to rewind all the windings.

The process of assembling the welder is quite simple:

1. The transformer is dismantled.
2. Carefully remove the secondary winding.
3. Two shunts are removed.
4. A secondary winding of two or three turns is made of thick wire (with a diameter of at least 10 mm).
5. Electrodes for resistance welding are made from a copper rod with a diameter larger than the wires.

Homemade spot welding tool

Useful DIY items for fishing

Among the homemade products you can find a lot interesting ideas for use in hiking conditions, as well as hunting and fishing.

Electronic alarm

An example would be an electronic signaling device for fishing with a regular fishing rod or other equipment. A simple biting device can be assembled in just half an hour. For it you will need an old beeper keychain and a strip of plastic 1-2 mm thick.

Alarm assembly:

1. The keychain is attached to the rod.
2. A strip of plastic is glued to the fishing line and inserted between the contacts of the key fob.

Now when the fish bites, the fish will pull the line, the plastic will fly out, the contacts will close and the key fob will work.

Underwater camera for ice fishing

Using a homemade underwater camera to winter fishing you can see if there is fish under the hole. And this simplifies the fishing process.

To make it you will need:

• small camera;
• sealed camera box;
• small TV;
• car battery to power the camera;
• extension;
• inverter;
• lead for cargo;
• ultraviolet diodes for illumination during underwater shooting;
• superglue, electrical tape, sealant.

Build process:

1. Two holes are made in the upper part of the box. An extension cable is inserted through one. Through the second is the wire that connects the camera to the TV.
2. Several more holes are made in the box into which light bulbs are inserted for illumination. The wires from the light bulbs are soldered into one circuit (for example, with a parallel arrangement), which is connected to a cable that provides power.
3. The holes are sealed with glue and tape for a tight seal.
4. Lead is melted and small elongated bars are poured out of it. They are placed at the bottom of the box.
5. Set up the camera and connect it to the cable. After which it is carefully placed in the box so that it has a clear forward and horizontal direction and transmits a high-quality image. For stability, the chamber is surrounded by soft material.
6. A torso (rope, belt) is attached to the box, which will be used to lower the camera to depth. For convenience, you can combine it, the power cable and the communication wire between the video camera and the TV into one core, secured with electrical tape.
7. Connect the power cable of the video camera to the battery and test the device.

Homemade fish bait

You can make a good bait for fishing yourself. This will be a device assembled based on a simple multivibrator.

You will need:

• sound emitter, for example, from a children's toy;
• wires;
• a small plastic jar, for example, for medicinal tablets;
• electronic board;
• regulator with plastic rod;
• a piece of foam;
• batteries;
• weights for the float;
• volume control.

The bait is assembled as follows:

1. You need to solder the circuit and check it.
2. Two wires are soldered to the sound emitter. Then they are carried inside the case and connected to the board.
3. A regulator with a plastic rod is placed in the lid of the jar.
4. A dense circle cut out of foam plastic is installed on top of the board, which separates the board from the battery.
5. Weights are attached to the bottom of the jar so that the container floats on the water like a float.
6. The regulator sets the frequency and changes the sound.

Bait scheme - 1 Bait scheme - 2

Electronic homemade products for cars

Car enthusiasts create homemade products with their own hands to improve appearance and ease of use of the car.

Electrical auto tester

A simple homemade electrical probe is perfect for a car. It can show the presence of a voltage of 12 volts in an electrical circuit. It is used to check the serviceability of relays, as well as light bulbs and other equipment. You can make such a device from a syringe and LEDs.

Assembly diagram:

1. Two LEDs are soldered with opposite terminals (plus one to the minus of the other and vice versa).
2. A steel probe is connected to one of the solders through a resistance of 300 Ohms. To the other solder there is a contact for batteries.
3. The design is inserted into the syringe so that the probe comes out of the hole for the needles. Most of the probe is insulated with a PVC tube.
4. 4 LR44 batteries are inserted into the syringe so that one of the poles is connected to the LED contact.
5. The other pole of the batteries is connected to a flexible wire with an alligator clip.

The video explains how to make a syringe tester. Filmed by ILYANOV channel.

Light switch

The scheme for smoothly turning off the lights in the car interior is quite simple to manufacture. Such electronics are suitable for any car. A small board consisting of a capacitor and diodes is soldered parallel to the interior lamp terminals. The drop in electricity voltage will occur gradually and create the effect of a gradually fading light.

Car subwoofer

To make a car subwoofer with your own hands, you must first purchase a speaker. You need to start from its dimensions when calculating the size of the case.

The simplest and most successful form of a subwoofer for the trunk is a truncated pyramid with a slope similar to that of the rear seats.

LED fog lights

You can make LED car fog lights with your own hands.

For creativity you will need:

• two ten-watt LEDs;
• 2 lenses from an old projector;
• gaskets from plastic pipes;
• LM317T microcircuits;
• resistors.

Instructions for assembling the craft:

1. LEDs are installed on pre-prepared aluminum radiators.
2. The structure is assembled from headlight housings, lenses from projectors, gaskets and diodes on radiators.
3. The fog lights are powered through current stabilizers on LM317T microcircuits and resistors.

Car carrying

A very convenient car carrier is made from a computer USB lamp. It is compact and you can connect the device to any place in the car wiring.

Manufacturing scheme:

1. Remove the contacts from the USB plug.
2. In the plug body we connect the wires of the lamp and the car alligator clips.
3. For mounting in in the right place(even horizontally), a magnet is placed on the plug.

Simple logic probe

A simple logic probe consists of two independent threshold devices, one of which is triggered by an input voltage corresponding to a logical "1", and the second - by a logical "O".

When the voltage at the probe input is between 0 and +0.4 V, transistors V7 and V8 are off, transistor V9 is off and V10 is on, the green LED V6 is on, indicating "0".

When the input voltage is from +0.4 to +2.3 V, transistors V7 and V8 are still closed, V9 is open, V10 is closed. LEDs do not light up. At a voltage above +2.3 V, transistors V8, V9 open and the red LED V5 lights up, indicating “1”. Diodes V1-V4 serve to increase the voltage at which the threshold device is activated, indicating “1”.

The current transfer coefficient of the transistors must be at least 400. The adjustment is made by selecting R5* and R7* according to the clear response of threshold devices at a voltage from +0.4 V to +2.4 V.

Network "CONTROL"

Typically, finder probes with neon bulbs are used to detect mains voltage. Alas, nowadays even such a sample is not easy to acquire. But it is quite simple to assemble a control device, the diagram of which is shown in the figure.

Improved led indicator mains voltage

I propose for repetition by radio amateurs an improved LED indicator of mains voltage, which differs from all previously published ones in being more noise-resistant. For example, the indicators shown in Fig. 1 and Fig. 2 are capable of giving false readings when the presence of voltage in a long cable is checked, and the cable has a broken phase wire. These indicators also give false readings when they are used to check the presence of voltage in network wiring with poor insulation - in basements, damp rooms, i.e. where there is low insulation resistance.

The proposed indicator (Fig. 3) is easy to manufacture and reliable in operation, free of false readings under any operating conditions. They can check both linear voltage 380 V and phase voltage. And it differs from all previous ones by using the KN102D dinistor in the circuit. Thanks to the latter, the indicator registers only the pure phase and does not respond to interference. The indicator uses a capacitor C1 - MBM 0.1 μF at 400 V and a resistor R1 - MLT 0.5.

Simple transistor tester

A simple transistor tester allows you to check the performance of bipolar transistors of n-p-n- and p-n-p-structures.

The transistor being tested, together with one of the V1 or V2 installed in the device (depending on the structure of the transistor being tested, determined by the position of switch S1), forms a multivibrator that generates low-frequency oscillations. Indicators of the presence of oscillations, and therefore the health of the transistor being tested, are the LEDs V3 and V4, which flash at the frequency generated by the multivibrator.

This device can test small, medium and, in some cases, transistors high power. Using resistor R1, the amplification properties of the low-power transistor being tested are assessed (approximately) - the greater the resistance of the introduced part of the resistor, at which the multivibrator is still operating, the higher the current transfer coefficient of this transistor. The device is powered by one 3336L battery.

Automatic light switch

The machine consists of a light sensor - a photoresistor and a photorelay made on transistors VI, V2, an actuator circuit on thyristors V4, V10 and a full-wave rectifier on diodes V6, V7. The machine works as follows. With decreasing illumination, the resistance of photoresistor R3 increases from 1...2 kOhm to 3...5 MOhm, which leads to an increase in the collector current of transistors VI and V2. As a result of this, thyristor V4 opens, the chain R7, SZ, V9 generates a pulse that opens thyristor V10, and the lighting lamps turn on. As the illumination of the photoresistor increases, its resistance decreases, and the collector current of transistor V2 also decreases, which leads to the blocking of thyristors V4 and V10. The lighting lamps go out, and the capacitor SZ is discharged through the diode V8 and resistors R5, R6 and R7. The switching threshold of the machine is set by resistor R1.

Details .

Variable resistor R1 type SPO-0.5, resistors type MLT-0.5; photoresistors of types SF2-2, SF2-5 or FSK-1; transistors - any low-frequency p-p-p structures with B>50; capacitor C2 type MBM, MBGC, MBGP for a voltage of 400 V.

When setting up, it is necessary to select resistors R5-R7, achieving reliable opening of thyristor V10 at the photorelay operating threshold specified (by resistor R1).

Power supply for analog and digital circuits

The power supply for analog and digital microcircuits consists of three stabilized rectifiers, two of which form a bipolar 12.6 V voltage source with separate regulation.

The adjustment is made using trimming resistors R6 and R9. The lower (according to the circuit) stabilizer provides a voltage of 5 V, which can also be adjusted with resistor R10.

The unified power transformer TAN 59-127/220-50 can be replaced with a homemade one with a magnetic core Ш 12 X 20. Network winding I at 220 V should have 3000 turns of PEV-2 wire - 0.12, winding II - 180 turns PEV-2 - ODZ , winding III - 220 turns of PEV-2 - 0.38 and winding IV - 70 turns of wire PEV-2 0.41. Different number turns in windings II and III at the same voltage at the output of the stabilizer arms in this power supply design is explained by the fact that a current of 60 mA is consumed from the upper (according to the circuit) arm, and 350 mA from the lower arm. If, according to operating conditions, these currents must be equal, an equal number of turns of wire of the same diameter should be wound.

Instead of "neon"

Capacitor C1 is used as a wattless resistance; diodes VD1-VD4 protect speaker BA1 from sudden surges of current during on-off moments; resistor R1 serves to discharge C1 after turning on the device.
Capacitor C1 must have a voltage of at least 400 V and a capacity of 1-2 μF. Speaker - 0.25GD19 or any other, with a power of more than 0.25 W with an internal resistance of 6-10 Ohms. Instead of a speaker, you can use a telephone capsule, for example, "TON-1", while the capacitance C1 is reduced to 0.01 μF. The device is mounted mounted in a housing made of dielectric material.

High precision thermostat

A high-precision thermostat with a pulsed master-control circuit was proposed by I. Boeris and A. Titov. It has a high stability of maintaining a constant temperature (up to ±0.05°C in the range from 20 to 80°C). It can be used in thermostats, calorimeters and other devices with power consumption up to 1 kW.

The regulating circuit consists of a thermistor R6 type MMT-1 with diode V6, a variable resistor R7 with diode V7 with capacitor C4. The control circuit is powered by a stabilizer using zener diodes V3 and V4, connected to the secondary winding of the step-down transformer T1.

The amount of current through thyristors VI and V2, and therefore through the heater, depends on the charge and discharge time constants of capacitor C4, which are determined by the ratio of the resistances of resistors R6 and R7. As the temperature increases, the resistance of the thermistor decreases, as a result of which the discharge current of capacitor C4 through the thermistor and diode V6 increases and the voltage on capacitor C4 decreases. The control voltage supplied to the thyristors through the current amplifier contains direct and alternating components. The variable component is formed using a phase shifter (R3C1) and goes through capacitor C2 to the base of transistor V8. This ensures a smooth change in the cutoff angle of the thyristor current, and therefore the current through the load.

Details. Transformer T1 is made on a magnetic circuit Ш12 X 15: winding I contains 4000 turns of PEV-1 0.1 wire, winding II contains 300 turns of PEV-1 0.29 wire.

The setup comes down to selecting resistors R1 and R4. The voltages at the anodes of the thyristors must be in phase, otherwise the terminals of winding II of the transformer should be swapped.

Diode generator

The property of germanium diodes to have a negative section on the reverse branch of the current-voltage characteristic is used in a generator-relaxator.

This generator can be used as a probe, a source of sound vibrations when voicing toys, etc. The voltage amplitude at the output of the generator is about 14 V. Its disadvantage is that a lot of power is released at the diode, exceeding the maximum permissible. It is advisable to install the diode on the radiator and operate the generator for a short time. It is impossible to reduce the capacitance of capacitor C1 to a value less than 0.15 µF.

Every day there are more and more, many new articles appear, it is quite difficult for new visitors to immediately find their bearings and review at once everything that has already been written and previously posted.

I would really like to draw the attention of all visitors to individual articles that were posted on the site earlier. In order to avoid having to search for the necessary information for a long time, I will make several “entrance pages” with links to the most interesting and useful articles on individual topics.

Let's call the first such page "Useful electronic homemade products." Here we consider simple electronic circuits, which are available for implementation to people of any level of training. The circuits are built using a modern electronic base.

All information in the articles is presented in a very accessible form and to the extent necessary for practical work. Naturally, to implement such schemes you need to understand at least the basics of electronics.

So, a selection of the most interesting articles on the site on the topic "Useful electronic homemade products". The author of the articles is Boris Aladyshkin.

Modern electronics components greatly simplify circuit design. Even a regular twilight switch can now be assembled from just three parts.

The article describes a simple and reliable electric pump control circuit. Despite the extreme simplicity of the circuit, the device can operate in two modes: water lifting and drainage.

The article provides several diagrams of spot welding machines.

Using the described design, you can determine whether a mechanism located in another room or building is working or not. Information about the operation is the vibration of the mechanism itself.

A story about what a safety transformer is, why it is needed and how you can make it yourself.

Description simple device, disconnecting the load if the mains voltage goes beyond permissible limits.

The article discusses the circuit of a simple thermostat using an adjustable zener diode TL431.

An article about how to make a device for smoothly switching on lamps using the KR1182PM1 microcircuit.

Sometimes, when the voltage in the network is low or when soldering massive parts, it becomes simply impossible to use a soldering iron. This is where a boost power regulator for a soldering iron can come to the rescue.

An article about how you can replace a mechanical thermostat for an oil heating radiator.

Description of a simple and reliable thermostat circuit for a heating system.

The article describes a converter circuit made on a modern element base, containing a minimum number of parts and allowing to obtain significant power in the load.

Article about in various ways connecting the load to the control unit on microcircuits using relays and thyristors.

Description of a simple control circuit for LED garlands.

Design simple timer, allowing you to turn the load on and off at specified time intervals. Working time and pause time do not depend on each other.

Description of the circuit and operating principle of a simple emergency lamp based on an energy-saving lamp.

A detailed story about the popular “laser-ironing” technology for manufacturing printed circuit boards, its features and nuances.

Those who do radio electronics at home are usually very inquisitive. Amateur radio circuits and homemade products will help you find a new direction in your creativity. Perhaps someone will find an original solution to this or that problem. Some homemade products use ready-made devices, connecting them in different ways. For others, you need to completely create the circuit yourself and make the necessary adjustments.

One of the simplest homemade products. More suitable for those who are just starting to craft. If you have an old but working cell phone with a button to turn on the player, you can use it, for example, to make a doorbell for your room. The advantages of such a call:

First you need to make sure that the selected phone is capable of producing a sufficiently loud melody, after which it must be completely disassembled. Basically, the parts are secured with screws or staples, which are carefully folded back. When disassembling, you will need to remember what goes with what, so that later you can put everything back together.

The player's power button is unsoldered on the board, and two short wires are soldered in its place. These wires are then glued to the board so the solder doesn't come off. The phone is going. All that remains is to connect the phone to the call button via a two-wire wire.

Homemade products for cars

Modern cars are equipped with everything you need. However, there are times when it is simply necessary homemade devices. For example, something broke, they gave it to a friend, and the like. That’s when the ability to create electronics with your own hands at home will be very useful.

The first thing you can tamper with without fear of damaging your car is the battery. If you don’t have a battery charger at hand at the right time, you can quickly assemble it yourself. To do this you will need:

A transformer from a tube TV is ideal. Therefore, those who are interested in homemade electronics never throw away electrical appliances in the hope that they will be needed someday. Unfortunately, two types of transformers were used: with one and with two coils. To charge a battery at 6 volts, any will do, but for 12 volts only two.

The wrapping paper of such a transformer shows the winding terminals, the voltage for each winding and the operating current. To power filaments vacuum tubes a voltage of 6.3 V with high current is used. The transformer can be remade by removing the extra secondary windings, or you can leave everything as is. In this case, the primary and secondary windings are connected in series. Each primary is rated at 127 V, so combining them produces 220 V. The secondary are connected in series to produce an output of 12.6 V.

Diodes must withstand a current of at least 10 A. Each diode requires a radiator with an area of ​​at least 25 square centimeters. They are connected into a diode bridge. Any electrical insulating plate is suitable for fastening. A 0.5 A fuse is included in the primary circuit, and a 10 A fuse in the secondary circuit. The device does not tolerate short circuits, so the polarity should not be confused when connecting the battery.

Simple heaters

During the cold season, it may be necessary to warm up the engine. If the car is parked where it is electricity, this problem can be solved using a heat gun. To make it you will need:

• asbestos pipe;
• nichrome wire;
• fan;
• switch.

Diameter asbestos pipe selected according to the size of the fan that will be used. The performance of the heater will depend on its power. The length of the pipe is everyone's preference. You can assemble a heating element and a fan in it, or just a heater. When choosing the latter option, you will have to think about how to allow air flow to the heating element. This can be done, for example, by placing all components in a sealed housing.

Nichrome wire is also selected according to the fan. The more powerful the latter, the larger diameter nichrome can be used. The wire is twisted into a spiral and placed inside the pipe. For fastening, bolts are used that are inserted into the drilled holes in the pipe. The length of the spiral and their number are selected experimentally. It is advisable that the coil does not become red hot when the fan is running.

The choice of fan will determine what voltage needs to be supplied to the heater. When using a 220 V electric fan, you will not need to use an additional power source.

The entire heater is connected to the network via a cord with a plug, but it itself must have its own switch. It can be either just a toggle switch or an automatic machine. The second option is more preferable; it allows you to protect the general network. To do this, the operation current of the machine must be less than the operation current of the room machine. A switch is also needed to quickly turn off the heater in case of problems, for example, if the fan does not work. This heater has its disadvantages:

• harmful to the body from asbestos pipes;
• noise from a running fan;
• smell from dust falling on the heated coil;
• fire hazard.

Some problems can be solved by using another homemade product. Instead of an asbestos pipe, you can use a coffee can. To prevent the spiral from closing on the jar, it is attached to a textolite frame, which is fixed with glue. A cooler is used as a fan. To power it, you will need to collect another electronic device- a small rectifier.

Homemade products bring those who do them not only satisfaction, but also benefits. With their help, you can save energy, for example, by turning off electrical appliances that you forgot to turn off. A time relay can be used for this purpose.

The simplest way to create a time-setting element is to use the charging or discharging time of a capacitor through a resistor. Such a chain is included in the base of the transistor. The circuit will require the following parts:

• high-capacity electrolytic capacitor;
• transistor p-n-p type;
• electromagnetic relay;
• diode;
• variable resistor;
• fixed resistors;
• DC source.

First you need to determine what current will be switched through the relay. If the load is very powerful, you will need to connect it. magnetic switch. The starter coil can be connected via a relay. It is important that the relay contacts can operate freely without sticking. Based on the selected relay, a transistor is selected and it is determined what current and voltage it can operate with. You can focus on KT973A.

The base of the transistor is connected through a limiting resistor to a capacitor, which, in turn, is connected through a bipolar switch. The free contact of the switch is connected through a resistor to the power supply negative. This is necessary to discharge the capacitor. The resistor acts as a current limiter.

The capacitor itself is connected to the positive bus of the power source through a variable resistor with high resistance. By selecting the capacitance of the capacitor and the resistance of the resistor, you can change the delay time interval. The relay coil is shunted by a diode, which turns on in the opposite direction. This circuit uses KD 105 B. It closes the circuit when the relay is de-energized, protecting the transistor from breakdown.

The scheme works as follows. In the initial state, the base of the transistor is disconnected from the capacitor, and the transistor is closed. When the switch is turned on, the base is connected to the discharged capacitor, the transistor opens and supplies voltage to the relay. The relay operates, closes its contacts and supplies voltage to the load.

The capacitor begins to charge through a resistor connected to the positive terminal of the power source. As the capacitor charges, the base voltage begins to rise. At a certain voltage value, the transistor closes, de-energizing the relay. The relay switches off the load. In order for the circuit to work again, you need to discharge the capacitor; to do this, switch the switch.