A variety of simple circuits on the NE555. Timer on the NE555 chip (on and off)

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What to do if you want to manage outdated equipment in the same way?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, fan or 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, 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.

We continue the review timer 555. In this article, we will consider examples of the practical application of this microcircuit. The theoretical review can be read.

Example No. 1 - Darkness signaling device.

The circuit beeps when it gets dark. While the photoresistor is lit, pin #4 is set low, which means the NE555 is in reset mode. But as soon as the lighting drops, the resistance of the photoresistor increases and a high level appears at pin #4 and as a result, the timer starts, emitting a beep.

Example No. 2 - Signaling module.

The diagram represents one of the car alarm modules, which gives a signal when the angle of the car changes. A mercury switch is used as a sensor. In the initial state, the sensor is not closed and the NE555 output is set to a low level. When the angle of the car changes, the mercury drop closes the contacts, and a low level at pin #2 starts the timer.

As a result, a high level appears at the output, which controls some actuator. Even after opening the sensor contacts, the timer will still remain active. You can turn it off if you stop the timer by applying a low level to pin #4. C1 is a 0.1uF ceramic capacitor ().

Example #3 - Metronome.

A metronome is a device used by musicians. It counts the required rhythm, which can be adjusted with a variable resistor. The circuit is built according to the scheme of a rectangular pulse generator. The metronome frequency is determined by the RC chain.

Example #4 - Timer.

Timer for 10 minutes. The timer is turned on by pressing the "Start" button, while the HL1 LED lights up. After the selected time interval, the HL2 LED lights up. A variable resistor can be used to adjust the time interval.

Example #5 - Schmitt trigger on 555 timer.

This is a very simple but effective scheme. The circuit allows, by supplying a noisy analog signal to the input, to obtain a clean rectangular signal at the output.

Example No. 6 - Precise generator.

Generator of increased accuracy and stability. The frequency is adjusted by resistor R1. Diodes - any germanium. You can also use Schottky diodes.

Read the continuation of "NE555 Timer Applications - Part 2".

Watch the video: Application of the NE555 timer

Portable USB oscilloscope, 2 channels, 40 MHz....

Chip NE555(analogous to KR1006VI1) is a universal timer designed to generate single and repetitive pulses with stable time characteristics. It is not expensive and is widely used in various amateur radio circuits. On it you can assemble various generators, modulators, converters, time relays, threshold devices and other components of electronic equipment ...

The microcircuit operates with a supply voltage from 5 V to 15 V. At a supply voltage of 5 V, the voltage levels at the outputs are compatible with TTL levels.

Dimensions for different enclosure types

BODY - DIMENSIONS
PDIP (8) - 9.81 mm × 6.35 mm
SOP - (8) - 6.20 mm × 5.30 mm
TSSOP (8) - 3.00 mm × 4.40 mm
SOIC (8) - 4.90 mm × 3.91 mm

Block diagram of NE555

Electrical characteristics

PARAMETER	TEST CONDITIONS		SE555			NA555 NE555 SA555			ED. MEAS.
			MIN	TYPE	MAX	MIN	TYPE	MAX
Voltage level at the THRES pin	VCC=15V		9.4	10	10.6	8.8	10	11.2	V
	VCC=5V		2.7	3.3	4	2.4	3.3	4.2
Current (1) through the THRES pin				30	250		30	250	nA
Voltage level at the TRIG pin	VCC=15V		4.8	5	5.2	4.5	5	5.6	V
		T A = -55°C to 125°C	3		6
	VCC=5V		1.45	1.67	1.9	1.1	1.67	2.2
		T A = -55°C to 125°C			1.9
Current through the TRIG pin	at 0 V on TRIG			0.5	0.9		0.5	2	µA
Voltage level at the RESET pin			0.3	0.7	1	0.3	0.7	1	V
	T A = -55°C to 125°C				1.1
Current through the RESET pin	at V CC on RESET			0.1	0.4		0.1	0.4	mA
	at 0 V to RESET			–0.4	–1		–0.4	–1.5
Switching current on DISCH in closed state				20	100		20	100	nA
Switching voltage on DISCH open	V CC = 5 V, I O = 8 mA						0.15	0.4	V
Voltage at CONT	VCC=15V		9.6	10	10.4	9	10	11	V
		T A = -55°C to 125°C	9.6		10.4
	VCC=5V		2.9	3.3	3.8	2.6	3.3	4
		T A = -55°C to 125°C	2.9		3.8
Low output voltage	V CC = 15 V, I OL = 10 mA			0.1	0.15		0.1	0.25	V
		T A = -55°C to 125°C			0.2
	VCC=15V, IOL=50mA			0.4	0.5		0.4	0.75
		T A = -55°C to 125°C			1
	VCC=15V, IOL=100mA			2	2.2		2	2.5
		T A = -55°C to 125°C			2.7
	V CC = 15 V, I OL = 200 mA			2.5			2.5
	VCC = 5V, IOL = 3.5mA	T A = -55°C to 125°C			0.35
	VCC = 5V, IOL = 5mA			0.1	0.2		0.1	0.35
		T A = -55°C to 125°C			0.8
	VCC = 5V, IOL = 8mA			0.15	0.25		0.15	0.4
High output voltage	V CC = 15 V, I OH = -100 mA		13	13.3		12.75	13.3		V
		T A = -55°C to 125°C	12
	V CC = 15 V, I OH = -200 mA			12.5			12.5
	V CC = 5 V, I OH = -100 mA		3	3.3		2.75	3.3
		T A = -55°C to 125°C	2
Current consumption		VCC=15V		10	12		10	15	mA
		VCC=5V		3	5		3	6
	Low output, no load	VCC=15V		9	10		9	13
		VCC=5V		2	4		2	5

(1) This parameter affects the maximum values ​​of the timing resistors R A and R B in the circuit. 12. For example, when V CC = 5 V R = R A + R B ≉ 3.4 MΩ, and for V CC = 15 V, the maximum value is 10 mΩ.

Performance characteristics

PARAMETER		TEST CONDITIONS (2)	SE555			NA555 NE555 SA555			ED. MEAS.
			MIN.	A TYPE.	MAX.	MIN.	A TYPE.	MAX.
Initial error time intervals (3)		T A = 25°C		0.5	1.5 (1)		1	3	%
				1.5			2.25
Time interval temperature coefficient	Each timer, monostable (4)	T A = MIN to MAX		30	100 (1)		50		ppm/ °C
	Each timer, unstable (5)			90			150
Changing the time interval from the supply voltage	Each timer, monostable (4)	T A = 25°C		0.05	0.2 (1)		0.1	0.5	%/V
	Each timer, unstable (5)			0.15			0.3
Output pulse rise time		C L \u003d 15 pF, T A = 25°C		100	200 (1)		100	300	ns
Fall time of the output pulse		C L \u003d 15 pF, T A = 25°C		100	200 (1)		100	300	ns

(1) Conform to MIL-PRF-38535, these parameters have not been tested in production.

(2) For conditions specified as Min. and Max. , use the appropriate value given in the recommended operating conditions.

(3) Time interval error is defined as the difference between measured meaning and average random sample from each process.

(4) Values ​​are for monostable circuit with the following component values ​​R A = 2 kΩ to 100 kΩ, C = 0.1 µF.

(5) Values ​​are for astable circuit with the following component values ​​R A = 1 kΩ to 100 kΩ, C = 0.1 µF.

Metal detector on a single chip

Coil diameter 70-90 mm, 250-290 turns of wire in varnish insulation (PEL, PEV ...), 0.2-0.4 mm in diameter.

Instead of a speaker, you can use headphones or a piezo emitter.

Video of this metal detector

Voltage converter from 12V to 24V

Toy animation

Together with the counter 4017 and 555, you can make a "running fire" to animate some kind of toy or souvenir. When the power is turned on, the generator starts running at 555 for only a few minutes, then turns off. At the same time, the current consumption drops - the batteries will last for a long time. The time is set with a 500 kΩ variable resistor.

Light controlled generator

Dark detector with LM555. This scheme will generate sound when light falls on the photocell Cds . Sveta . The sensor, when exposed to light, closes the circuit and 555 generates oscillations of about 1 kHz through open transistor BC158.

musical keyboard

A very simple musical instrument (keyboard) for playing music can be made using a 555 chip. You can assemble an unusual musical instrument in the photo above. Graphite is used as a keyboard and a sheet of paper with notes is presented as holes in the paper.

The same circuit, but with conventional resistors and buttons.

Timer for 10 minutes

The timer is started with the S1 button after 10 minutes. LED1 and LED2 flash alternately. The time is set by a 550 kΩ resistor and a 150 microfarad capacitor.

car alarm simulator

The LED flashes as if the car has an alarm. Mount the LED in a visible place. The thief will see that the car is under the alarm and bypass it 🙂

A simple police siren simulator

The circuit is assembled on a breadboard.

With two NE555s, you can make a simple police siren generator. It is recommended that you do the following: the timer R1=68 kOhm (timer #1) is set to slow generation mode and the timer with R4=10 kOhm (timer #2) is set to fast generation mode. MYou can change the characteristics of the timer. The output frequency is changed by resistors R1, R2 and C1 for timer #1 and R4, R5 and C3 for timer #2.

A similar circuit is below with a transistor at the output:

Liquid Level Sonic Generator

You can use this water level control circuit to signaling anywhere like level indicator water, e.g. in tanks, tanks, basins or anywhere else.

This is not all the possibilities of the timer chip. See also the video of the microcircuit.

With the modern development of electronics in China, it seems that you can buy anything your heart desires: from home theaters and computers to such simple products as electrical sockets and plugs.

Somewhere between them are flashing Christmas tree garlands, clocks with thermometers, power regulators, thermostats, photo relays and much more. As the great satirist Arkady Raikin said in a monologue about the deficit: “Let everything be, but let something be missing!” In general, what is missing is just what is included in the "repertoire" of simple amateur radio designs.

Despite such competition from the Chinese industry, the interest of amateur designers in these simple designs has not been lost to this day. They continue to be developed and in some cases find worthy application in small home automation devices. Many of these devices were born thanks to (domestic analogue KR1006VI1).

These are the already mentioned photo relays, various simple alarm systems, voltage converters, PWM - DC motor controllers and much more. The following will describe several practical designs available for repetition at home.

Photo relay on timer 555

The photorelay shown in Figure 1 is designed to control lighting.

Picture 1.

The control algorithm is traditional: in the evening, when the illumination decreases, the light turns on. Turning off the light bulb occurs in the morning when the illumination reaches a normal level. The circuit consists of three nodes: a light meter, a load switching node and a power supply. It is better to start the description of the operation of the circuit backwards - forwards - the power supply, the load switching unit and the light meter.

Power Supply

In such designs, just the very case when it is reasonable to use, violating all safety recommendations, a power supply that does not have galvanic isolation from the network. When asked why this is possible, the answer will be: after setting up the device, no one will get into it, everything will be in an insulating case.

External adjustments are also not foreseen, after setting it remains only to close the lid and hang it ready in place, let it work for itself. Of course, if necessary, the only setting "sensitivity" can be brought out with a long plastic tube.

During the configuration process, security can be provided in two ways. Either use an isolation transformer () or power the device from a laboratory power supply. In this case, the mains voltage and the light bulb can not be connected, and the operation of the photocell can be controlled by LED1.

The power supply circuit is quite simple. It represents a bridge rectifier Br1 with a quenching capacitor C2 for an alternating voltage of at least 400V. Resistor R5 is designed to smooth the surge of current through the capacitor C14 (500.0uF * 50V) when the device is turned on, and also "in combination" is a fuse.

Zener diode D1 is designed to stabilize the voltage at C14. As a zener diode, 1N4467 or 1N5022A is suitable. For the Br1 rectifier, 1N4407 diodes or any low-power bridge, with a reverse voltage of 400V and a rectified current of at least 500mA, are quite suitable.

Capacitor C2 should be shunted with a resistor with a resistance of about 1 MΩ (not shown in the diagram) so that after the device is turned off, the current does not “click”: to kill, of course, will not kill, but still quite sensitive and unpleasant.

Load switching unit

Made using a specialized chip KR1182PM1A, which allows you to make a lot of useful devices. In this case, it is used to control the triac KU208G. The best results are obtained by the imported "analog" BT139 - 600: the load current is 16A at a reverse voltage of 600V, and the control electrode current is much less than that of the KU208G (sometimes the KU208G has to be selected according to this indicator). BT139 is capable of withstanding surge overloads up to 240A, which makes it extremely reliable when working in various devices.

If the BT139 is mounted on a heatsink, the switching power can reach 1KW, without a heatsink it is possible to control a load up to 400W. In the case when the power of the light bulb does not exceed 150W, you can completely do without a triac. To do this, the output of the La1 lamp, right according to the scheme, should be connected directly to the terminals 14, 15 of the microcircuit, and the resistor R3 and the triac T1 should be excluded from the circuit.

Let's go further. The KR1182PM1A microcircuit is controlled through pins 5 and 6: when they are closed, the lamp is off. There may be an ordinary contact switch, however, it works the other way around - the switch is closed and the lamp is off. It's much easier to remember this "logic" this way.

If this contact is opened, then the capacitor C13 begins to charge and, as the voltage across it increases, the brightness of the lamp gradually increases. For incandescent lamps, this is very important, as it increases their service life.

By selecting the resistor R4, you can adjust the degree of charge of the capacitor C13 and the brightness of the lamp. In the case of using energy-saving lamps, the capacitor C13 can be omitted, as well as the KR1182PM1A itself. But this will be discussed below.

Now let's get to the main point. Instead of a relay, simply out of a desire to get rid of contacts, control was entrusted to the AOT128 transistor optocoupler, which can be successfully replaced with an imported “analogue” 4N35, however, with such a replacement, the value of the resistor R6 should be increased to 800KΩ ... 1MΩ, since the imported 4N35 will not work at 100KΩ will. Proven by practice!

If the optocoupler transistor is open, its K-E transition, like a contact, will close terminals 5 and 6 of the KR1182PM1A microcircuit and the lamp will be turned off. To open this transistor, you need to light up the LED of the optocoupler. In general, it turns out the opposite: the LED is off, and the lamp is on.

Based on 555, it turns out very simply. To do this, it is enough to connect the photoresistor LDR1 connected in series and the tuning resistor R7 to the inputs of the timer, with its help the threshold for the operation of the photorelay is adjusted. Switching hysteresis (dark - light) is provided by the timer itself, its . Remember those "magic" numbers 1/3U and 2/3U?

If the photosensor is in the dark, its resistance is high, so the voltage across the resistor R7 is low, which leads to the fact that the timer output (pin 3) is set high and the optocoupler LED is off, and the transistor is closed. Therefore, the light bulb will be turned on, as it was written earlier in the subheading "Load switching node".

If the photo sensor is illuminated, its resistance becomes small, on the order of several kΩ, so the voltage across the resistor R7 increases to 2/3U, and a low voltage level appears at the timer output, the optocoupler LED lights up, and the load lamp goes out.

Here someone may say: “It will be difficult!”. But almost always everything can be simplified to the limit. If it is intended to light energy-saving lamps, then soft start is not required, and a conventional relay can be used. And who said that only lamps and only turn on?

If the relay has several contacts, then you can do whatever you want, and not only turn it on, but also turn it off. Such a scheme is shown in Figure 2 and does not need special comments. The relay is selected from the conditions so that the coil current is not more than 200mA at an operating voltage of 12V.

Figure 2.

Pre-Installation Diagrams

In some cases, it is required to turn on something with some delay relative to turning on the power of the device. For example, first apply voltage to the logic circuits, and after a while, power the output stages.

Such delays are implemented on the 555 timer quite simply. Schemes of such delays and timing diagrams of operation are shown in Figures 3 and 4. The dotted line shows the voltage of the power source, and the solid line shows the output of the microcircuit.

Figure 3. After power-up, the delayed output goes high.

Figure 4. After power-up, the delayed output goes low.

Most often, such "installers" are used as components of more complex circuits.

Alarm devices on the 555 timer

The signaling circuit is a one that we have already met for a long time.

Figure 5

Two electrodes are immersed in a container with water, for example, a pool. While they are in water, the resistance between them is small (water is a good conductor), so the capacitor C1 is shunted, the voltage across it is close to zero. Also, zero voltage at the input of the timer (pins 2 and 6), therefore, a high level will be set at the output (pin 3), the generator does not work.

If for some reason the water level drops and the electrodes are in the air, the resistance between them will increase, ideally just a break, and the capacitor C1 will not be shunted. Therefore, our multivibrator will work - pulses will appear at the output.

The frequency of these pulses depends on our imagination and on the parameters of the RC circuit: it will be either a flashing light or a nasty speaker squeak. Along with this, you can turn on topping up the water. To avoid overflow and turn off the pump in time, it is necessary to add another electrode to the device and a similar circuit. Here the reader can already experiment.

Figure 6.

When you press the limit switch S2, a high level voltage appears at the output of the timer, and will remain so even if S2 is released and no longer held. The device can be removed from this state only by pressing the "Reset" button.

While we stop here, maybe someone will need time to take a soldering iron and try to solder the considered devices, explore how they work, at least experiment with the parameters of RC circuits. Listen to how the speaker beeps or the LED blinks, compare what the calculations give, whether the practical results differ much from the calculated ones.

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.