DIY digital timer. Timer connection diagram

To ensure the logic of the operation of electrical devices, it is often necessary to take into account some given time period. To do this, various timers and time relays are included in the circuit. Today, most of these devices can be purchased on the Internet, but if you wish, you can make a time switch yourself. Moreover, such a homemade product will always find application in solving any household problems.

A few words about varieties

Electronic timers for setting on and off delays are used in microwave ovens, washing machines, heating systems, smart home, etc. is based on setting the time interval for the delay in the operation of the electrical network. In practice, such a device can have a different way of slowing down:

• electromagnetic;

Rice. 1: electromagnetic timing relays

• pneumatic;
• with clockwork;

Rice. 2. Clockwork

• motor;
• electronic.

Due to the complexity of the settings and the lack of certain elements, not all time relays can be assembled by hand. The simplest option for manufacturing and reviewing are electronic models, since today you can get components for them both from old equipment and from any radio parts store.

Electromechanical relays and other options are available if specific accessories are available, which are not always found in the free market.

What will be needed for manufacturing?

Depending on the chosen model, the process can be both simple and quite laborious. Therefore, it is better to stock up on everything you need in advance so as not to stop halfway through the work done.

To assemble the time relay you will need:

• a set of radio components - in each specific example of a home-made relay, their list will be different, but the main nomenclature will remain unchanged (microcircuits, intermediate relays or switches, power supplies or step-down transformers, coils, etc.);
• the basis for a set of elements - a printed circuit board, a dielectric surface or a frame, are also selected based on local conditions;

Rice. 3. PCB

• soldering iron, solder and other devices for connecting circuit elements.
• housing - to protect the relay elements from various mechanical influences, dust, moisture and weeds;
• control or programming unit - if you plan to make an adjustable delay.

In some situations, the above parts can be borrowed from old electronic devices if they suit you, otherwise they must be purchased. You can decide on a specific list after you select the specific model that you want to make.

We create a time relay for 12 and 220 Volts

Depending on the magnitude of the supply voltage to which the load is connected, the potential level under which the elements of the time relay will be located is also determined. In practice, to create time delays, both those operating from the 220V network and from safe low 12V are used.

The first option is considered simpler, since the work is carried out directly from the network. Also, the 220 V circuit is relevant for powering a particularly powerful load - engines or household appliances.

Idea 1. On diodes

Consider a variant of the simplest logic element for operation in a 220V circuit.

Rice. 4. Time relay circuit for 220V

Here, switching on occurs when the S1 button is pressed, after which voltage is applied to the diode bridge. From the bridge, the potential passes to the timing element, consisting of resistors and a capacitor. In the process of accumulating charge, the thyristor VS1 will open, and the current will flow through the lighting lamp L1. When the capacitance of the capacitor is fully charged, the thyristor will go into the closed state, after which the relay is activated and the lamp will stop burning.

The maximum shutter speed here can be set to several tens of seconds, since its value will be set by the resistance of the resistor and capacitance. A significant drawback is that this circuit poses a threat to human life in case of electric shock. Therefore, we will further consider an example of manufacturing a 12V time relay.

Idea 2. On transistors

The principle of operation of such a time relay is based on the use of semiconductor devices for the task of the time interval. In practice, circuits with one transistor, as well as with a large number, can be used. The most relevant for self-production of time relays on two transistors - they are characterized by better stability and controllability.

An example of such an electronic device is shown in the figure below:

Rice. 5. On transistors

For its practical implementation, you will need to acquire the following elements:

• resistors - one for 100 kOhm and three for 1 kOhm;
• two transistors KT3102B or identical;
• a capacitor to create an off / on delay;
• button to start the time relay;
• intermediate relay or switch;
• status LED;
• printed circuit board for assembling all parts.

The principle of operation of such a time relay is to apply a voltage of 12 V to the capacitive element C1. After that, the capacitor is charged to a certain potential, the value of which will be sufficient to open the transistor VT1.

The charge current for a capacitive element is determined by the resistance of the branch C1 - R1 - the greater the resistance, the lower the current, and the charge accumulation time is longer. Accordingly, to increase or decrease the time to turn on or turn off the load, you can use a variable resistor for R1.

Rice. 6. Install a variable resistor

After the capacitance is discharged, an opening signal will be sent to the base of the transistor VT1, and the electric current will begin to flow through the emitter and collector, resistors R2 and R3. These resistor values ​​are selected to open the second transistor VT2, which operates in the electronic key mode to turn on the main load.

Open VT2 supplies voltage to the relay winding K1, the core in it is attracted and performs operations with the load. One of the pairs of contacts of the electromagnetic relay acts with its contacts on the power supply circuit of the LED, signaling the state of the device.

The SB1 button in the circuit allows you to reset the capacitor charge - this is a mandatory procedure before each subsequent start, which presents certain difficulties that are solved by installing microcircuits.

Idea 3. Based on microcircuits

This is more complex than using transistors, but the digital relay does not require a button to be pressed to start a new cycle, they are more stable. The cyclic relay allows you to perform several operations in automatic mode, due to the presence of a microcircuit, there is an internal reference power source, you can significantly increase the time delay limits.

Rice. 7. Based on the KR512PS10 chip

Look at the figure, the circuit shown here is designed to work in a 220 V circuit. To implement it, you will need resistors of different ratings indicated in the diagram, a diode bridge, a pair of transistors, semiconductor elements, capacitors, an intermediate relay, a microcircuit.

Its principle of operation is identical to the previously described version on two transistors, with the difference that a microcircuit appears in the time delay control circuit. With the help of which the capacitor charge can accumulate ten times longer, respectively, it becomes possible to increase the delay time.

The assembly process is not particularly difficult for experienced radio amateurs with the skills of soldering and reading circuits. However, for beginners, such a time relay can present a certain difficulty, so they should be attentive to the process.

Idea 4. Based on the NE555 timer

This option also applies to electronic relays, in which the time delay is set using the popular NE555 timer. With it, you can assemble a timer that operates with switching processes, both on and off.

Rice. 8. Based on NE555 timer

As you can see in the diagram, the timer acts as a control key that allows the issuance of an electrical signal either directly to the device or through the operating element - the relay coil. When the timing chain of two resistors and a capacitor reaches saturation, the timer will output a control signal to the time relay output, which will attract the core to the device coil and close the contacts. An LED is connected in parallel to the output coil, indicating the state of the relay.

The practical implementation of this scheme also requires certain skills and knowledge in soldering radio components and manufacturing printed circuit boards.

It should be noted that the timer and the microcircuit, although they provide more stable operation, cannot boast of the ability to program. Modern cyclic timers on microcontrollers provide unlimited functions in the formation of the logic of work, but it is quite difficult to assemble them at home.

Video ideas

The time relay is installed in many models of equipment and household appliances. This device allows you to automatically turn on or off the equipment and not waste time controlling certain actions. Craftsmen often design various devices for their own needs. For many designs, it is required to make a time relay with your own hands, since branded devices are not always suitable in a particular situation. However, before proceeding with the manufacture of a homemade timer, novice craftsmen are advised to familiarize themselves with the main types of such relays and the principles of their operation.

How an electronic timer works

Unlike the very first clockwork timers, modern time relays are much faster and more efficient. Many of them are based on microcontrollers (MCs) capable of performing millions of operations per second.

This speed is not needed to turn on and off, so the microcontrollers were connected to timers that could count the pulses that occur inside the MK. Thus, the central processor executes its main program, and the timer provides timely actions at certain intervals. Understanding the principle of operation of these devices will be needed even when making a simple do-it-yourself capacitive time relay.

The principle of operation of the time relay:

• After the start command, the timer starts counting from zero.
• Under the action of each pulse, the contents of the counter increase by one and gradually acquire the maximum value.
• Next, the contents of the counter are reset to zero, since it becomes “overflowing”. At this point, the time delay ends.

This simple design allows you to get a maximum shutter speed within 255 microseconds. However, in most devices, seconds, minutes, and even hours are required, which raises the question of how to create the required time intervals.

The way out of this situation is quite simple. When the timer overflows, this event causes the main program to abort. Next, the processor switches to the corresponding subroutine, which combines small excerpts with any period of time that is required at the moment. This interrupt service routine is very short, consisting of no more than a few dozen instructions. At the end of its action, all functions return to the main program, which continues to work from the same place.

The usual repetition of commands does not occur mechanically, but under the guidance of a special command that reserves memory and creates short time delays.

The main types of time relays

When designing a homemade time relay, a specific model is taken as a sample. Therefore, each master must imagine the main devices that perform the functions of timers. The main task of any time relay is to obtain a delay between the input and output signal. Various methods are used to create such a delay.

Electromechanical relays include pneumatic devices. Their design includes an electromagnetic drive and a pneumatic attachment. The coil of the device is designed for alternating current with an operating voltage of 12 to 660 V - a total of 16 exact ratings are installed. The operating frequency is 50-60 Hz. With these parameters, a do-it-yourself time relay for 12v can be made. Depending on the design, the delay for such relays begins when the electromagnetic actuator is activated or when it is released.

The time is set using a screw that regulates the cross section of the hole through which air exits the chamber. The parameters of these devices are not stable, so time relays are more widely used.

These devices use a specialized chip KR512PS10. It is energized through a rectifier bridge and a stabilizer, after which the internal oscillator of the microcircuit begins to generate pulses. To adjust their frequency, a variable resistor is used, displayed on the front panel of the device and connected in series with a capacitor that sets the time. The counting of the received pulses is carried out by a counter having a variable division ratio. These designs can be taken as a basis for making a cyclic time relay and other similar devices.

Modern time relays are made on the basis of microcontrollers and are unlikely to be suitable for home craftsmen as a sample. If you need to get the exact time intervals, it is recommended to use the finished product.

Do-it-yourself time relay 220v circuit

Quite often, for designs made by home craftsmen, it is required to make a simple do-it-yourself time relay. Reliable and inexpensive timers fully justify themselves during operation.

The basis of most home-made devices is the same KR512PS10 microcircuit, which is powered through a parametric stabilizer with a stabilization voltage of about 5 V. When the power is turned on, a circuit consisting of a resistor and a capacitor forms a reset pulse of the microcircuit. At the same time, the internal oscillator is started, in which the frequency is set by a chain of another resistor and a capacitor. After that, the internal counter of the microcircuit starts counting pulses.

The number of pulses is also the division factor of the counter. This parameter is set by switching the outputs of the microcircuit. When the output reaches a high level, the counter stops. At the other output, the pulses also reach a high level, as a result, VT1 opens. Through it, relay K1 is switched on, the contacts of which directly control the load. This circuit is ideal for solving the problem of how to make a 220v time relay with your own hands. To restart the time delay, it is enough to turn off the relay for a short time and then turn it on again.

In the video tutorial of the Jakson Parcel and Homemade Package Reviews channel, we will assemble a time relay circuit based on a timer chip on the NE555. Very simple - few details, which will not be difficult to solder everything with your own hands. However, it will be useful to many.

Radio components for time relay

You will need the microcircuit itself, two simple resistors, a 3 microfarad capacitor, a 0.01 microfarad non-polar capacitor, a KT315 transistor, almost any diode, one relay. The supply voltage of the device will be from 9 to 14 volts. You can buy radio components or a ready-assembled time relay in this Chinese store.

The scheme is very simple.

Anyone can do it, given the necessary details. Assembly on a printed breadboard that will turn everything compact. As a result, part of the board will have to be broken off. You will need a simple button without a latch, it will activate the relay. Also two variable resistors, instead of the one required in the circuit, since the master does not have the required value. 2 megaohm. Two 1 megaohm resistors in series. Also, a relay, the supply voltage is 12 volts DC, it can pass through itself 250 volts, 10 amperes AC.

After assembly, as a result, the time relay based on the 555 timer looks like this.

Everything is compact. The only thing that visually spoils the view is the diode, since it has such a shape that it cannot be soldered otherwise, since its legs are much wider than the holes in the board. It still turned out pretty good.

Checking the device on the 555 timer

Let's check our relay. The indicator of work will be an LED strip. Let's connect a multimeter. Let's check - we press the button, the LED strip lights up. The voltage supplied to the relay is 12.5 volts. The voltage is now at zero, but for some reason the LEDs are on - most likely a relay malfunction. It is old, soldered from an unnecessary board.

By changing the position of the trimming resistors, we can adjust the relay operating time. Let's measure the maximum and minimum time. It turns off almost immediately. And maximum time. It took about 2-3 minutes - you can see for yourself.

But such indicators are only in the presented case. They may be different for you, because it depends on the variable resistor that you will use and on the capacitance of the electric capacitor. The larger the capacity, the longer your time relay will work.

Conclusion

We assembled an interesting device today on the NE 555. Everything works fine. The scheme is not very complicated, many will be able to master it without problems. In China, some analogues of such schemes are sold, but it is more interesting to assemble it yourself, it will be cheaper. Anyone can find the use of such a device in everyday life. For example, street light. You left the house, turned on the street lighting and after a while it turns off by itself, just when you have already left.

See everything in the video about assembling the circuit on a 555 timer.

It is possible to activate and deactivate household appliances without the presence and participation of the user. Most of the models produced today are equipped with a timer for automatic start / stop.

What to do if you want to manage outdated equipment in the same way? Stock up on patience, our advice and make a time relay with your own hands - believe me, this homemade product will be used in the household.

We are ready to help you realize an interesting idea and try your hand at the path of an independent electrical engineer. For you, we have found and systematized all the valuable information about the options and methods for manufacturing relays. The use of the information provided guarantees easy assembly and excellent performance of the instrument.

In the article proposed for study, home-made versions of the device tested in practice are analyzed in detail. The information is based on the experience of enthusiastic electrical craftsmen and the requirements of regulations.

Man has always sought to make his life easier by introducing various devices into everyday life. With the advent of technology based on an electric motor, the question arose of equipping it with a timer that would automatically control this equipment.

Turned on for a specified time - and you can go do other things. The unit will turn itself off after the set period. For such automation, a relay with an auto-timer function was required.

A classic example of the device in question is in a relay in an old Soviet-style washing machine. On its body there was a pen with several divisions. I set the desired mode, and the drum spins for 5-10 minutes, until the clock inside reaches zero.

The electromagnetic time switch is small in size, consumes little electricity, has no broken moving parts and is durable

Today they are installed in various equipment:

• microwave ovens, ovens and other household appliances;
• exhaust fans;
• automatic watering systems;
• lighting control automation.

In most cases, the device is made on the basis of a microcontroller, which simultaneously controls all other modes of operation of automated equipment. It's cheaper for the manufacturer. No need to spend money on several separate devices responsible for one thing.

According to the type of element at the output, the time relay is classified into three types:

• relay - the load is connected through a "dry contact";
• triac;
• thyristor.

The first option is the most reliable and resistant to surges in the network. A device with a switching thyristor at the output should be taken only if the connected load is insensitive to the shape of the supply voltage.

To make a time relay yourself, you can also use a microcontroller. However, homemade products are mainly made for simple things and working conditions. An expensive programmable controller in such a situation is a waste of money.

There are much simpler and cheaper circuits based on transistors and capacitors. Moreover, there are several options, there are plenty to choose from for your specific needs.

Schemes of various homemade products

All the proposed do-it-yourself manufacturing options for time relays are built on the principle of starting a set shutter speed. First, a timer is started with a specified time interval and a countdown.

The external device connected to it starts working - the electric motor or the light turns on. And then, upon reaching zero, the relay gives a signal to turn off this load or block the current.

Option # 1: the easiest on transistors

Transistor-based circuits are the easiest to implement. The simplest of them includes only eight elements. To connect them, you don’t even need a board, everything can be soldered without it. A similar relay is often made to connect lighting through it. I pressed the button - and the light is on for a couple of minutes, and then turns itself off.

To power this circuit, 9 or 12 volt batteries are required, and such a relay can also be powered from 220 V variables using a 12 V DC converter (+)

To assemble this homemade time relay, you will need:

• a pair of resistors (100 Ohm and 2.2 mOhm);
• bipolar transistor KT937A (or analogue);
• load switching relay;
• 820 ohm variable resistor (for adjusting the time interval);
• capacitor at 3300 uF and 25 V;
• rectifier diode KD105B;
• switch to start the countdown.

The time delay in this relay-timer occurs due to the charging of the capacitor to the power level of the transistor key. While C1 is charging to 9-12 V, the key in VT1 remains open. External load is powered (light on).

After some time, which depends on the value set on R1, the transistor VT1 closes. Relay K1 eventually de-energizes and the load is de-energized.

The charge time of the capacitor C1 is determined by the product of its capacitance and the total resistance of the charging circuit (R1 and R2). Moreover, the first of these resistances is fixed, and the second is adjustable to set a specific interval.

The timing parameters for the assembled relay are selected empirically by setting different values ​​on R1. To later make it easier to set the desired time, markings with minute-by-minute positioning should be made on the case.

It is problematic to specify the formula for calculating the issued delays for such a scheme. Much depends on the parameters of a particular transistor and other elements.

Bringing the relay to its original position is performed by reverse switching S1. The capacitor closes on R2 and discharges. After switching on S1 again, the cycle starts anew.

In a circuit with two transistors, the first one is involved in the regulation and control of the time pause. And the second is an electronic key for turning on and off the power of an external load.

The most difficult thing in this modification is to accurately select the resistance R3. It should be such that the relay closes only when a signal is applied from B2. In this case, the reverse switching on of the load must occur only when B1 is triggered. It will have to be selected experimentally.

This type of transistor has a very low gate current. If the resistance winding in the control relay-key is selected large (tens of ohms and MΩ), then the shutdown interval can be increased to several hours. Moreover, most of the time, the relay-timer practically does not consume energy.

The active mode in it begins in the last third of this interval. If the RV is connected through a conventional battery, then it will last a very long time.

Option #2: Chip-based

Transistor circuits have two main disadvantages. For them, it is difficult to calculate the delay time and before the next start it is required to discharge the capacitor. The use of microcircuits eliminates these shortcomings, but complicates the device.

However, if you have even minimal skills and knowledge in electrical engineering, making such a time relay with your own hands is also not difficult.

The opening threshold of the TL431 is more stable due to the presence of a reference voltage source inside. Plus, it requires a much higher voltage to switch it. At the maximum, by increasing the value of R2, it can be raised to 30 V.

The capacitor will take a long time to charge to such values. In addition, connecting C1 to the resistance for discharging in this case occurs automatically. Additionally, you do not need to click on SB1 here.

Another option is to use the "integral timer" NE555. In this case, the delay is also determined by the parameters of the two resistors (R2 and R4) and the capacitor (C1).

“Turning off” the relay occurs due to the switching again of the transistor. Only its closure here is performed by a signal from the output of the microcircuit, when it counts the necessary seconds.

There are much fewer false positives when using microcircuits than when using transistors. The currents in this case are more tightly controlled, the transistor opens and closes exactly when required.

Another classic microcircuit version of the time relay is based on the KR512PS10. In this case, when the power is turned on, the R1C1 circuit supplies a reset pulse to the input of the microcircuit, after which the internal generator starts in it. The shutdown frequency (division ratio) of the latter is set by the control circuit R2C2.

The number of pulses to be counted is determined by switching the five outputs M01-M05 in various combinations. The delay time can be set from 3 seconds to 30 hours.

After counting the specified number of pulses, the output of the Q1 chip is set to a high level, which opens VT1. As a result, relay K1 is activated and turns the load on or off.

The assembly scheme of the time relay using the KR512PS10 microcircuit is not complicated, resetting to the initial state in such a PB occurs automatically when the specified parameters are reached by connecting the legs 10 (END) and 3 (ST) (+)

There are even more complex time relay circuits based on microcontrollers. However, they are not suitable for self-assembly. There are difficulties with both soldering and programming. Variations with transistors and the simplest microcircuits for domestic use are enough in the vast majority of cases.

Option #3: powered by 220V output

All of the above circuits are designed for a 12-volt output voltage. To connect a powerful load to a time relay assembled on their basis, it is necessary at the output. To control electric motors or other complex electrical equipment with increased power, you will have to do this.

However, to adjust household lighting, you can assemble a relay based on a diode bridge and a thyristor. At the same time, it is not recommended to connect anything else through such a timer. The thyristor passes through itself only the positive part of the sine wave of 220 Volt variables.

For an incandescent bulb, a fan or a heating element, this is not scary, and other electrical equipment of this kind may not withstand and burn out.

The time relay circuit with a thyristor at the output and a diode bridge at the input is designed to operate in 220 V networks, but has a number of restrictions on the type of connected load (+)

To assemble such a timer for a light bulb, you need:

• constant resistance at 4.3 MΩ (R1) and 200 Ω (R2) plus adjustable at 1.5 kΩ (R3);
• four diodes with a maximum current above 1 A and a reverse voltage of 400 V;
• 0.47 uF capacitor;
• thyristor VT151 or similar;
• switch.

This relay-timer functions according to the general scheme for such devices, with the gradual charging of the capacitor. When the contacts are closed on S1, C1 starts charging.

During this process thyristor VS1 remains open. As a result, a mains voltage of 220 V is supplied to the load L1. After charging C1 is completed, the thyristor closes and cuts off the current, turning off the lamp.

The delay is adjusted by setting the value on R3 and selecting the capacitance of the capacitor. At the same time, it must be remembered that any touch to the bare legs of all used elements threatens with electric shock. They are all powered by 220V.

If you don’t want to experiment and assemble the time relay yourself, you can choose ready-made options for switches and sockets with a timer.

More information about such devices is written in the articles:

Conclusions and useful video on the topic

Understanding the internals of a time relay from scratch is often difficult. Some lack knowledge, while others lack experience. To make it easier for you to choose the right circuit, we have made a selection of videos that describe in detail all the nuances of the operation and assembly of the electronic device in question.

If you need a simple device, then it is better to take a transistor circuit. But to accurately control the delay time, you will have to solder one of the options on a particular microcircuit.

If you have experience in assembling such a device, please share the information with our readers. Leave comments, attach photos of your homemade products and participate in discussions. The contact block is located below.

Timer circuit on the counter K561IE16

The design is made on only one chip K561IE16. Since, for its correct operation, an external clock generator is needed, in our case we will replace it with a simple blinking LED.

As soon as we apply voltage to the timer circuit, the capacitance C1 will start charging through the resistor R2 therefore, a logical unit will briefly appear on pin 11, resetting the counter. The transistor connected to the meter output will open and turn on the relay, which will connect the load through its contacts.

With flashing LED with frequency 1.4 Hz pulses are sent to the clock input of the counter. With each pulse transition, a counter is counted. Through 256 impulses or about three minutes, a logical unit level will appear at pin 12 of the counter, and the transistor will close, turning off the relay and the load switched through its contacts. In addition, this logical unit passes to the DD clock input, stopping the timer. The operating time of the timer can be selected by connecting point "A" of the circuit to various outputs of the counter.

The timer circuit is made on a microcircuit KR512PS10, which has in its internal composition a binary counter-divider and a multivibrator. Like a conventional counter, this microcircuit has a division ratio from 2048 to 235929600. The choice of the required ratio is set by applying logic signals to the control inputs M1, M2, M3, M4, M5.

For our timer circuit, the division factor is 1310720. The timer has six fixed time intervals: half an hour, an hour and a half, three hours, six hours, twelve hours and a day of an hour. The frequency of operation of the built-in multivibrator is determined by the resistor values R2 and capacitor C2. When switching switch SA2, the frequency of the multivibrator changes, and passing through the counter-divider and the time interval.

The timer circuit starts immediately after power is turned on, or you can press the SA1 toggle switch to reset the timer. In the initial state, the ninth output will be a logical unit level, and the tenth inverse output, respectively, will be zero. As a result, the transistor VT1 connect the LED part of the optothyristors DA1, DA2. The thyristor part has an anti-parallel connection, this allows you to adjust the alternating voltage.

At the end of the countdown, the ninth output will go to zero and turn off the load. And at output 10, a unit will appear, which will stop the counter.

The start of the timer circuit is carried out by pressing one of the three buttons with fixing the time interval, while it starts the countdown. Parallel to pressing the button, the LED corresponding to the button lights up.

At the end of the time interval, the timer emits an audible signal. A subsequent press will disable the circuit. Time intervals are changed by the denominations of the radio components R2, R3, R4 and C1.

Timer circuit, which provides a turn-off delay, is shown in the first figure. Here, a p-type transistor (2) is included in the load power circuit, and an n-type transistor (1) controls it.

The timer circuit works as follows. In the initial state, the capacitor C1 is discharged, both transistors are closed and the load is de-energized. With a short press on the Start button, the gate of the second transistor is connected to a common wire, the voltage between its source and gate becomes equal to the supply voltage, it instantly opens, connecting the load. The voltage surge that occurred on it through the capacitor C1 enters the gate of the first transistor, which also opens, so the gate of the second transistor will remain connected to the common wire even after the button is released.

As the capacitor C1 is charged through the resistor R1, the voltage across it rises, and at the gate of the first transistor (relative to the common wire) it decreases. After some time, depending mainly on the capacitance of the capacitor C1 and the resistance of the resistor R1, it decreases so much that the transistor starts to close and the voltage at its drain rises. This leads to a decrease in the voltage at the gate of the second transistor, so the latter also begins to close and the voltage at the load decreases. As a result, the gate voltage of the first transistor begins to decrease even faster.

The process proceeds like an avalanche, and soon both transistors close, de-energizing the load, the capacitor C1 quickly discharges through the diode VD1 and the load. The device is ready to start again. Since the field-effect transistors of the assembly begin to open at a gate-source voltage of 2.5 ... 3 V, and the maximum allowable voltage between the gate and source is 20 V, the device can operate at a supply voltage of 5 to 20 V (nominal voltage of capacitor C1 should be a few volts more than the supply). The turn-off delay time depends not only on the parameters of the elements C1, R1, but also on the supply voltage. For example, increasing the supply voltage from 5 to 10 V leads to its increase by about 1.5 times (with the values ​​of the elements indicated in the diagram, it was 50 and 75 s, respectively).

If, with closed transistors, the voltage across resistor R2 turns out to be more than 0.5 V, then its resistance must be reduced. A device that provides a turn-on delay can be assembled according to the circuit shown in Fig. 2. Here, the assembly transistors are turned on in much the same way, but the voltage to the gate of the first transistor and capacitor C1 is supplied through resistor R2. In the initial state (after connecting the power source or after pressing the SB1 button), the capacitor C1 is discharged and both transistors are closed, so the load is de-energized. As it charges through resistors R1 and R2, the voltage on the capacitor rises, and when it reaches a value of about 2.5 V, the first transistor begins to open, the voltage drop across resistor R3 increases and the second transistor also begins to open. When the voltage at the load rises so much that the diode VD1 opens, the voltage across the resistor R1 rises. This leads to the fact that the first transistor, and after it the second one, open faster and the device abruptly switches to the open state, closing the load power circuit

The timer circuit is a restart, for this you need to press the button and hold it in this state for 2 ... 3 s (this time is enough to completely discharge the capacitor C1). The timers are mounted on printed circuit boards made of fiberglass foiled on one side, the drawings of which are shown respectively in Fig. 3 and 4. The boards are designed for the use of a diode of the KD521, KD522 series and parts for surface mounting (resistors R1-12, size 1206 and a tantalum oxide capacitor). Setting up devices is reduced mainly to the selection of resistors to obtain the required time delay.

The described devices are designed to be included in the positive power cable of the load. However, since the IRF7309 assembly contains transistors with a channel of both types, it is not difficult to adapt the timers to include in the negative wire. To do this, the transistors should be swapped and reversed by switching on the diode and capacitor (naturally, this will require corresponding changes in the printed circuit board drawings). It should be noted that with long connecting wires or the absence of capacitors in the load, pickups on these wires and uncontrolled activation of the timer are possible.

Timer circuit for five minutes

If the time interval is more than 5 minutes, the device can be restarted and the countdown can be restarted.

After a short circuit SB1, the capacitance C1 starts charging, which is included in the collector circuit of the transistor VT1. The voltage from C1 is supplied to an amplifier with a large input impedance on transistors VT2- VT4. Its load is an LED indicator that turns on alternately after a minute.

The design allows you to choose one of five possible time intervals: 1.5, 3, 6, 12 and 24 hours. The load is connected to the AC mains at the start of the countdown and disconnected at the end of the countdown. Time intervals are set using a frequency divider of square wave signals generated by an RC multivibrator.

The master oscillator is made on the logical components DD1.1 and DD1.2 microcircuits K561LE5. The generation frequency is formed by an RC chain on R1,C1. The accuracy of the course is adjusted over the shortest time interval, by selecting the resistance R1 (temporarily, when adjusting, it is desirable to replace it with a variable resistance). To create the necessary time ranges, the pulses from the output of the multivibrator go to two counters DD2 and DD3, as a result, the frequency is divided.

These two counters - K561IE16 are connected in series, but for simultaneous reset, the reset pins are connected together. Reset occurs using switch SA1. Another toggle switch SA2 selects the required time range.

When a logical unit appears at the output of DD3, it goes to pin 6 of DD1.2, as a result of which the generation of pulses by the multivibrator ends. At the same time, the logical unit signal follows the input of the inverter DD1.3 to the output of which VT1 is connected. When a logical zero appears at the output of DD1.3, the transistor closes and turns off the LEDs of the optocouplers U1 and U2, and this turns off the triac VS1 and the load connected to it.

When the counters are reset, zeros are set at their outputs, including the output on which the SA2 switch is installed. At the input of DD1.3, zero is also supplied and, accordingly, a unit is output at its output, which connects the load to the network. Also, in parallel, the zero level will be set at the input 6 DD1.2, which will start the multivibrator, and the timer will start timing. The timer is powered by a transformerless circuit, consisting of components C2, VD1, VD2 and C3.

When the toggle switch SW1 is closed, the capacitor C1 begins to slowly charge through the resistance R1, and when the voltage level on it is 2/3 of the supply voltage, trigger IC1 will respond to this. In this case, the voltage at the third output will drop to zero, and the circuit with the bulb will open.

With a resistance of resistor R1 of 10M (0.25 W) and capacitance C1 of 47 uF x 25 V, the device will operate for about 9 and a half minutes, if desired, it can be changed by adjusting the ratings of R1 and C1. The dotted line in the figure indicates the inclusion of an additional switch, with which you can turn on the circuit with a light bulb even when the toggle switch is closed. The quiescent current of the design is only 150 μA. Transistor BD681 - composite (Darlington) medium power. Can be replaced by BD675A/677A/679A.

This timer circuit on the PIC16F628A microcontroller is borrowed from a good Portuguese site for electronics. The microcontroller is clocked from an internal oscillator, which can be considered accurate enough for this moment, since pins 15 and 16 remain free, an external quartz resonator can be used for even greater accuracy in operation.