Do-it-yourself timers for switching off electrical equipment. Very convenient countdown timer with digital LED display. Single transistor relay
Clock with audible alarm timer for controlling household appliances.
A timer is a device that set time turns the equipment on or off with its switching contacts. Real-time timers allow you to set the trigger time at a set time of day. The most simple example such a timer will be an alarm clock.
The scope of application of the timer is extensive:
- lighting control;
- watering management of home and garden plants;
- ventilation control;
- aquarium management;
- control of electric heaters and so on.
The proposed timer can be made quickly and inexpensively even by a novice radio amateur.
I made it based on the clock designer. ()
I needed to use a timer to control the watering of plants at the dacha.
Watch the entire manufacturing process in the video:
List of tools and materials
- any Digital Watch with audible alarm;
-screwdriver;
- scissors;
- soldering iron;
-cambric;
- two 12V relays;
-12V power supply from adapter;
- connecting wires;
- foil textolite for printed circuit board or breadboard;
-industrial or homemade time relay;
-resistor;
- transistors KT815 (or analogues);
-diode.
Step one. Timer board wiring.
Timer circuit
All that is needed is to solder the components according to the diagram onto a breadboard and solder two wires from the piezo emitter of the clock. We collect the simplest scheme with intermediate relay and transistor switch. When the first pulse of a sound signal is sent from the clock, relay P1 is turned on, the normally open contact closes and turns on the load, and at the same time, through the second normally open contact of relay P1 and the normally closed contact of the time relay, relay P1 self-locks. Together with the load, the time relay PB is turned on - the countdown of the specified load operating time begins. At the end of this time, RV opens the contact and relay P1 is de-energized, the load is turned off. The circuit is ready for the next cycle. The diode serves to prevent a reverse pulse into the clock circuit (any low-power diode can be used). LED to indicate load activation. In this circuit, you need an intermediate relay with two normally open contacts, but I didn’t have one - I used two Chinese relays (the coils are connected in parallel). If the load is more powerful, then accordingly you need to use a relay with more powerful contacts. I had a 12V adapter and installed its circuit directly on the breadboard. In principle, any low-power 12V power source can be used.
In short, the clock turns on the load and the time relay is turned off after the delay has expired.
If you do not have an industrial time relay, you can make it yourself using a simple scheme. As the capacitance of capacitor C1 increases, the operating time of the relay increases.
Step two. Checking the timer operation.
My circuit worked the first time I turned it on.
All that remains is to set the alarm time. My watch has two alarm time settings. For my case, it’s enough to turn on watering, for example, in the morning at 7 o’clock for one hour, and in the evening at 20 o’clock, water again. When you press the clock buttons, sound signals are emitted, so when setting, the timer circuit must be de-energized to prevent false alarms. My watch has a “chime” function - every hour from 8 to 20 o’clock, that is, in addition to the alarm clock, you can use these signals if necessary. If not necessary, then the “chimes” function is disabled.
This is how the weekend design turned out. It was interesting to test new scheme so everything was done quickly. In the future, it will be necessary to make a case and place a board and a time relay there. A beginner can make such a timer on his own without spending a lot of time and money. And where to use them is up to you to decide.
All the work took a couple of weekend evenings and 75 rubles (
Modern equipment often requires a timer, i.e. a device that does not work immediately, but after a period of time, which is why it is also called a delay relay. The device creates temporary delays in turning on or off other devices. It is not necessary to purchase it in a store, because a well-designed homemade time relay will effectively perform its functions.
Scope of application of time relay
Areas of use of the timer:
- regulators;
- sensors;
- automation;
- various mechanisms.
All these devices are divided into 2 classes:
- Cyclic.
- Intermediate.
The first is considered an independent device. It sends a signal after a specified time interval. In automatic systems, a cyclic device turns on and off the necessary mechanisms. It is used to control lighting:
- on the street;
- in aquarium;
- in the greenhouse.
The cyclic timer is an integral device in the system “ Smart House" It is used to perform the following tasks:
- Turning the heating on and off.
- Event reminder.
- At a strictly specified time, turns on the necessary devices: washing machine, kettle, light, etc.
In addition to the above, there are also industries in which cyclic delay relays are used:
- the science;
- medicine;
- robotics.
The intermediate relay is used for discrete circuits and serves auxiliary device. It performs automatic interruption electrical circuit. The scope of application of the intermediate timer relay begins where signal amplification and galvanic isolation of the electrical circuit are required. Intermediate timers are divided into types depending on their design:
- Pneumatic. The relay does not operate instantly after receiving a signal; the maximum response time is up to one minute. Used in control circuits of metal-cutting machines. The timer controls the drives for step adjustment.
- Motor. The time delay setting range starts from a couple of seconds and ends in tens of hours. Delay relays are part of overhead power line protection circuits.
- Electromagnetic. Designed for DC circuits. With their help, acceleration and braking of the electric drive occurs.
- With clock mechanism. The main element is a charged spring. Regulation time – from 0.1 to 20 seconds. Used in relay protection of overhead power lines.
- Electronic. The operating principle is based on physical processes (periodic pulses, charge, discharge of capacitance).
Schemes of various time relays
There are different versions of time relays, each type of circuit has its own characteristics. You can make timers yourself. Before you make a time relay with your own hands, you need to study its structure. Schemes of simple time relays:
- on transistors;
- on microcircuits;
- for output power 220 V.
Let's describe each of them in more detail.
Transistor circuit
Required radio components:
- Transistor KT 3102 (or KT 315) – 2 pcs.
- Capacitor.
- Resistor rated 100 kOhm (R1). You will also need 2 more resistors (R2 and R3), the resistance of which will be selected along with the capacitance depending on the timing of the timer.
- Button.
When the circuit is connected to a power source, the capacitor will begin to charge through resistors R2 and R3 and the emitter of the transistor. The latter will open, so the voltage will drop across the resistance. As a result, the second transistor will open, which will trigger the electromagnetic relay.
As the capacitance is charged, the current will decrease. This will cause the emitter current to decrease and the voltage drop across the resistance to a level that will cause the transistors to close and the relay to release. To restart the timer, you will need to briefly press the button, which will cause the tank to completely discharge.
To increase the time delay, use a circuit field effect transistor with insulated shutter.
Chip-based
The use of microcircuits will eliminate the need to discharge the capacitor and select the ratings of radio components to set the required response time.
Required electronic components for a 12 volt time relay:
- resistors with a nominal value of 100 Ohm, 100 kOhm, 510 kOhm;
- diode 1N4148;
- capacity 4700 uF and 16 V;
- button;
- TL 431 chip.
The positive pole of the power supply must be connected to the button, to which one relay contact is connected in parallel. The latter is also connected to a 100 Ohm resistor. On the other side, the resistor is connected to resistances of 510 and 100 kOhm. One of the terminals of the latter goes to the microcircuit. The second pin of the microcircuit is connected to a 510 kOhm resistor, and the third to a diode. A second relay contact is connected to the semiconductor device, which is connected to the actuator. The negative terminal of the power supply is connected to a 510 kΩ resistor.
For power supply 220 V
The two circuits described above are designed for a voltage of 12 V, i.e., they are not suitable for powerful loads. This drawback can be eliminated using a magnetic starter installed at the output.
If the load is a low-power device (household lighting, fan, tubular electric heater), then you can do without a magnetic starter. The role of a voltage converter will be performed by a diode bridge and a thyristor. Required parts:
- Diodes rated for currents greater than 1 A and reverse voltage not higher than 400 V, – 4 pcs.
- Thyristor VT 151 – 1 pc.
- Capacitance 470 nF – 1 pc.
- Resistors: 4300 kOhm – 1 pc., 200 Ohm – 1 pc., adjustable at 1500 Ohm – 1 pc.
- Switch.
The 220 V power supply is connected to the diode bridge contact and switch. The second contact of the bridge is connected to the switch. A thyristor is connected in parallel to the diode bridge. The thyristor is connected to a diode and resistances of 200, 1500 Ohms. The second terminals of the diode and resistor (200 Ohms) go to the capacitor. A resistance of 4300 kOhm is connected in parallel to the latter. But it must be remembered that this device is not used for powerful loads.
To ensure precise intervals of time when performing various actions using electrical equipment, time relays are used.
They are used everywhere in everyday life: electronic alarm clock, changing the operating modes of the washing machine, microwave oven, exhaust fans in the toilet and bathroom, automatic watering of plants, etc.
Advantages of timers
Of all the varieties, electronic devices are the most common. Their advantages:
- small sizes;
- exceptionally low energy consumption;
- no moving parts except for the electromagnetic relay mechanism;
- wide range of time exposures;
- independence of service life from the number of operating cycles.
Transistor time relay
With basic electrician skills, you can make an electronic time relay with your own hands. It is mounted in a plastic case, which houses the power supply, relay, board and control elements.
The simplest timer
The time relay (diagram below) connects the load to the power supply for a period of 1-60 seconds. The transistor switch controls the electronic relay K1, which connects the consumer to the network with contact K1.1.
In the initial state, switch S1 closes capacitor C1 to resistance R2, which keeps it discharged. Electromagnetic switch K1 does not work in this case, since the transistor is locked. When the capacitor is connected to the power supply (upper position of contact S1), its charging begins. A current flows through the base, which opens the transistor and K1 turns on, closing the load circuit. The supply voltage to the time relay is 12 volts.
As the capacitor charges, the base current gradually decreases. Accordingly, the magnitude of the collector current drops until K1, by turning off, opens the load circuit with contact K1.1.
To reconnect the load to the network for a specified period of operation, the circuit must be restarted again. To do this, the switch is set to the lower "off" position, which leads to the discharge of the capacitor. The device is then turned on again by S1 for a specified period of time. The delay is adjusted by installing resistor R1, and can also be changed if the capacitor is replaced with another one.
The principle of operation of a relay using a capacitor is based on its charging for a time depending on the product of the capacitance and the resistance of the electrical circuit.
Timer circuit with two transistors
It is not difficult to assemble a time relay with your own hands using two transistors. It starts working if you apply power to capacitor C1, after which it will begin charging. In this case, the base current opens transistor VT1. Following it, VT2 will open, and the electromagnet closes the contact, supplying power to the LED. Its glow will indicate that the time relay has activated. The circuit provides load switching R4.
As the capacitor charges, the emitter current gradually decreases until the transistor turns off. As a result, the relay will turn off and the LED will stop working.
The device restarts if you press the SB1 button and then release it. In this case, the capacitor will discharge and the process will repeat.
Operation begins when the 12V time relay is energized. For this purpose, autonomous sources can be used. When powered from the network, a power supply consisting of a transformer, rectifier and stabilizer is connected to the timer.
Time relay 220v
Most electronic circuits operate at low voltage with galvanic isolation from the network, but can still switch significant loads.
The time delay can be made from a 220V time relay. Everyone knows electromechanical devices with a delay in turning off the old washing machines. It was enough to turn the timer knob, and the device turned on the engine for a specified time.
Electromechanical timers have been replaced by electronic devices, which are also used for temporary lighting in the toilet, on the landing, in a photo enlarger, etc. In this case, contactless switches on thyristors are often used, where the circuit operates from a 220 V network.
Power is supplied through a diode bridge with a permissible current of 1 A or more. When the contact of switch S1 closes, in the process of charging capacitor C1, thyristor VS1 opens and lamp L1 lights up. It serves as a load. After fully charged the thyristor will close. This will be visible when the lamp turns off.
The lamp burns for a few seconds. It can be changed by installing capacitor C1 with a different value or connecting a 1 kOhm variable resistor to diode D5.
Time relay on microcircuits
Transistor timer circuits have many disadvantages: the difficulty of determining the delay time, the need to discharge the capacitor before the next start, and short response intervals. The NE555 chip, called the “integrated timer,” has long gained popularity. It is used in industry, but you can see many schemes for making time relays with your own hands.
The time delay is set by resistances R2, R4 and capacitor C1. The load connection contact K1.1 closes when the SB1 button is pressed, and then it opens independently after a delay, the duration of which is determined from the formula: t and = 1.1R2∙R4∙C1.
When you press the button again, the process repeats.
In many household appliances microcircuits with time relays are used. Instructions for use are a necessary attribute of proper operation. It is also compiled for do-it-yourself timers. Their reliability and durability depend on this.
The circuit operates from a simple 12 V power supply consisting of a transformer, diode bridge and capacitor. The current consumption is 50 mA, and the relay switches a load of up to 10 A. The adjustable delay can be made from 3 to 150 s.
Conclusion
For domestic purposes, you can easily assemble a time relay with your own hands. Electronic circuits work well on transistors and microcircuits. You can set a contactless timer on thyristors. It can be turned on without galvanic isolation from the existing network.
In the video tutorial of the channel “Reviews of parcels and homemade products from jakson” we will assemble a time relay circuit based on a timer chip on NE555. Very simple - there are few parts, so it won’t be difficult to solder everything with your own hands. At the same time, it will be useful to many.
Radio components for time relays
You will need the microcircuit itself, two simple resistors, a 3 microfarad capacitor, a 0.01 uF non-polar capacitor, a KT315 transistor, almost any diode, one relay. The device supply voltage will be from 9 to 14 volts. You can buy radio components or a ready-made time relay in this Chinese store.
The scheme is very simple.
Anyone can master it if they have the necessary parts. Assembly on a printed circuit board, which makes everything compact. As a result, part of the board will have to be broken off. You will need a simple button without a lock; it will activate the relay. Also two variable resistors, instead of one, which is required in the circuit, since the master does not have the required value. 2 megaohms. Two 1 megaohm resistors in series. Also, a relay with a supply voltage of 12 volts DC can pass through itself 250 volts, 10 amperes alternating current.
After assembly, this is what a time relay based on a 555 timer looks like.
Everything turned out compact. The only thing that visually spoils the appearance 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 a 555 timer
Let's check our relay. The operation indicator will be LED Strip Light. Let's also connect a multimeter. Let's check - 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 the relay is faulty. It is old, soldered from an unnecessary board.
By changing the position of the trimming resistors, we can adjust the operating time of the relay. Let's measure the maximum and minimum time. It turns off almost immediately. And maximum time. About 2-3 minutes passed - you can see for yourself.
But such indicators are only in the presented case. Yours may be different, since 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
Today we assembled an interesting device on the NE 555. Everything works great. The scheme is not very complicated, many will be able to master it without any problems. Some analogues of similar circuits are sold in China, but it is more interesting to assemble it yourself, it will be cheaper. Anyone can find a use for such a device in everyday life. For example, street light. You left the house, turned on the street lighting, and after some time it turned off by itself, just when you had already left.
Watch everything in the video about assembling the circuit on a 555 timer.
To ensure precise intervals of time when performing various actions using electrical equipment, time relays are used.
They are used everywhere in everyday life: electronic alarm clock, changing operating modes of a washing machine, microwave oven, exhaust fans in the toilet and bathroom, automatic watering of plants, etc.
Advantages of timers
Of all the varieties, electronic devices are the most common. Their advantages:
- small sizes;
- exceptionally low energy consumption;
- no moving parts except for the electromagnetic relay mechanism;
- wide range of time exposures;
- independence of service life from the number of operating cycles.
Transistor time relay
With basic electrician skills, you can make an electronic time relay with your own hands. It is mounted in a plastic case, which houses the power supply, relay, board and control elements.
The simplest timer
The time relay (diagram below) connects the load to the power supply for a period of 1-60 seconds. The transistor switch controls the electronic relay K1, which connects the consumer to the network with contact K1.1.
In the initial state, switch S1 closes capacitor C1 to resistance R2, which keeps it discharged. Electromagnetic switch K1 does not work in this case, since the transistor is locked. When the capacitor is connected to the power supply (upper position of contact S1), its charging begins. A current flows through the base, which opens the transistor and K1 turns on, closing the load circuit. The supply voltage to the time relay is 12 volts.
As the capacitor charges, the base current gradually decreases. Accordingly, the magnitude of the collector current drops until K1, by turning off, opens the load circuit with contact K1.1.
To reconnect the load to the network for a specified period of operation, the circuit must be restarted again. To do this, the switch is set to the lower "off" position, which leads to the discharge of the capacitor. The device is then turned on again by S1 for a specified period of time. The delay is adjusted by installing resistor R1, and can also be changed if the capacitor is replaced with another one.
The principle of operation of a relay using a capacitor is based on its charging for a time depending on the product of the capacitance and the resistance of the electrical circuit.
Timer circuit with two transistors
It is not difficult to assemble a time relay with your own hands using two transistors. It starts working if you apply power to capacitor C1, after which it will begin charging. In this case, the base current opens transistor VT1. Following it, VT2 will open, and the electromagnet closes the contact, supplying power to the LED. Its glow will indicate that the time relay has activated. The circuit provides load switching R4.
As the capacitor charges, the emitter current gradually decreases until the transistor turns off. As a result, the relay will turn off and the LED will stop working.
The device restarts if you press the SB1 button and then release it. In this case, the capacitor will discharge and the process will repeat.
Operation begins when the 12V time relay is energized. For this purpose, autonomous sources can be used. When powered from the network, a power supply consisting of a transformer, rectifier and stabilizer is connected to the timer.
Time relay 220v
Most electronic circuits operate at low voltage with galvanic isolation from the network, but can still switch significant loads.
The time delay can be made from a 220V time relay. Everyone knows electromechanical devices with a delay in turning off old washing machines. It was enough to turn the timer knob, and the device turned on the engine for a specified time.
Electromechanical timers have been replaced by electronic devices, which are also used for temporary lighting in the toilet, on the landing, in a photo enlarger, etc. In this case, contactless switches on thyristors are often used, where the circuit operates from a 220 V network.
Power is supplied through a diode bridge with a permissible current of 1 A or more. When the contact of switch S1 closes, in the process of charging capacitor C1, thyristor VS1 opens and lamp L1 lights up. It serves as a load. Once fully charged, the thyristor will close. This will be visible when the lamp turns off.
The lamp burns for a few seconds. It can be changed by installing capacitor C1 with a different value or connecting a 1 kOhm variable resistor to diode D5.
Time relay on microcircuits
Transistor timer circuits have many disadvantages: the difficulty of determining the delay time, the need to discharge the capacitor before the next start, and short response intervals. The NE555 chip, called the “integrated timer,” has long gained popularity. It is used in industry, but you can see many schemes for making time relays with your own hands.
The time delay is set by resistances R2, R4 and capacitor C1. The load connection contact K1.1 closes when the SB1 button is pressed, and then it opens independently after a delay, the duration of which is determined from the formula: t and = 1.1R2∙R4∙C1.
When you press the button again, the process repeats.
Many household appliances use microcircuits with time relays. Instructions for use are a necessary attribute of proper operation. It is also compiled for do-it-yourself timers. Their reliability and durability depend on this.
The circuit operates from a simple 12 V power supply consisting of a transformer, diode bridge and capacitor. The current consumption is 50 mA, and the relay switches a load of up to 10 A. The adjustable delay can be made from 3 to 150 s.
Conclusion
For domestic purposes, you can easily assemble a time relay with your own hands. Electronic circuits work well on transistors and microcircuits. You can set a contactless timer on thyristors. It can be turned on without galvanic isolation from the existing network.