Detailed description, application and circuit diagrams for switching on the NE555 timer

Let's look at examples of practical applications of this chip.

Schmidt trigger.

This is a very simple but effective scheme. The circuit allows, by applying an analog signal to the input, to obtain a pure rectangular signal at the output

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A simple timer for turning on the device at ~220V.

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Scheme for receiving more accurate intervals.

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Practical application in the article PWM for a fan

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Twilight Switch.

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Control your device with one button.

A version of such a scheme is in this blog.

Similar scheme one button control on CD4013 chip (similar to 561TM2)

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Water level control.

Circuit for inclusion LED backlight from autonomous power supply, for 10-30 seconds.

One application option is built into the front door near the keyhole.

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The backlight is turned on by pressing a button on the door handle - as a result, there will be no problems with opening the lock in the absence of natural or artificial light.

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Code lock on the NE555 timer.

I have not yet seen a similar development of a combination lock on the NE555 timer on the Internet, so this development is dedicated to all lovers of this wonderful microcircuit.
A circuit based on the NE555 chip in the form of a combination lock for a door or safe can be easily implemented using this timer.
I also know that the 555 works normally at low temperatures (if it is to be used outdoors) and has a wider supply voltage range of up to 16V. The reliability of the microcircuit is beyond doubt.

And so I give an example of a circuit in which the digital code will consist of 4 digits (technically, the circuit can be implemented on one button, but this would be too banal, I think that 4 digits are just right for a start, you can increase the number of digits in the code of this circuit to infinity (in identical parts block by block, circled U2 on the diagram).
In the above diagram, all 4 timers operate according to the same scheme; there are slight differences in timers U1, U4. The scheme U2 and U3 are repeated one to one.
Each timer in this circuit can be configured for its own working time; the time-setting chain R1, R2, C1 is used for this.
And also the secrecy of the code can be increased by connecting additional. switching diodes (as an example I gave the inclusion of one diode D1, I didn’t draw more, because I think that then the circuit would be very difficult to perceive).
The main difference between this circuit on 555 timers and similar circuits is the presence of a setting for the working time of each timer; given the simplicity of this circuit, the likelihood of an unauthorized person selecting the code will be very small.

Operation of the circuit;
- Press the zero button, timer U1 starts, its working time is set to hold logical one (pin 3) for 30 seconds, after which you can press button 1.
- Press button 1 of timer U2, its working time is set to 2 seconds, during this time you need to press button 2 (otherwise U2 holding logical one (pin 3) is reset and pressing button 2 will have no meaning)
- Press button 2, timer U3 is set to hold logical one (pin 3) for 25 seconds, after that you can press button 3, but……….. look at the switching diode D1, because of it there is no point in pressing button 3 quickly, until the 30 second working time of timer U1 expires,
- After pressing button 3, timer U4 outputs a logical one (U4 pin 3) to the actuator.
It remains to be added that in the current device the digital code will not be located in numerical order, but chaotically,
and any pressing of other buttons will reset the timers to 0.
Well, that’s all for now, I can’t describe all the use cases here, I see that not everything, I touched on here in the description...... in general, if you have an idea, its technical implementation will always be there.
All settings for the operating time of the U1…….U4 microcircuits are test ones and are described here as an example. :)
(in security systems for uninvited guests, the most difficult thing is individual solutions, proven by time)
I am attaching an archive with the circuit in Proteus, in which the operation of the circuit can be visually assessed.

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The purpose of the eight legs of the microcircuit.

1. Earth.

A pin that connects to the power supply negative and to the common wire of the circuit.
2. Launch.
Comparator input No. 2. When a low-level pulse (no more than 1/3 Vp) is applied to this input, the timer starts and a high-level voltage is set at the output for a time determined by the external resistance R (Ra + Rb,) and capacitor C - this is the so-called monostable multivibrator mode. The input pulse can be either rectangular or sinusoidal. The main thing is that its duration should be shorter than the charging time of capacitor C. If the input pulse nevertheless exceeds this time in duration, then the output of the microcircuit will remain in a high level state until the input level is set high again. The current consumed by the input does not exceed 500nA.

3. Exit.
The output voltage changes with the supply voltage and is equal to Vpit-1.7V (high output level). At a low level, the output voltage is approximately 0.25V (at a supply voltage of +5V). Switching between low and high states occurs in approximately 100 ns.
4. Reset.
When a low level voltage (no more than 0.7V) is applied to this pin, the output is reset to a low level state, regardless of what mode the timer is currently in and what it is doing. Reset, you know, it is reset. The input voltage is independent of the supply voltage - it is a TTL-compatible input. To prevent accidental resets, it is recommended to connect this pin to the power supply positive until it is needed.
5. Control.
This pin allows you to access the reference voltage of comparator No. 1, which is equal to 2/3Vsupply. Typically, this pin is not used. However, its use can significantly expand the possibilities of timer management. The thing is that by applying voltage to this pin, you can control the duration of the output pulses of the timer and thus drive the timing chain to RC. The voltage supplied to this input in monostable multivibrator mode can range from 45% to 90% of the supply voltage. And in multivibrator mode from 1.7 V to the supply voltage. In this case, we receive a FM (FM) modulated signal at the output. If this pin is not used, then it is recommended to connect it to the common wire through a 0.01 μF (10 nF) capacitor to reduce the level of interference and all other troubles.
6. Stop.
This pin is one of the inputs of comparator No. 1. It is used as a kind of antipode to pin 2. That is, it is used to stop the timer and bring the output to a low level state. When a high level pulse is applied (at least 2/3 of the supply voltage), the timer stops and the output is reset to a low level state. Just like pin 2, both rectangular and sinusoidal pulses can be supplied to this pin.
7. Discharge.
This pin is connected to the collector of transistor T6, the emitter of which is connected to ground. Thus, when the transistor is open, capacitor C is discharged through the collector-emitter junction and remains in a discharged state until the transistor closes. The transistor is open when the output of the microcircuit is low and closed when the output is active, that is, it is high. This pin can also be used as an auxiliary output. Its load capacity is approximately the same as that of a conventional timer output.

Electronic integrated circuits are a branch of our science and technology whose capabilities are far from being exhausted. Apparently, these are the sprouts of that same artificial intelligence about which so much has already been said. Moreover, if our natural intelligence is built on elements - neurons - which can be called electronic-chemical, then human-made integrated circuits are not found in nature. This is a pure invention of the human mind. It was obtained as a result of long work to improve the most ordinary electrical appliances that people needed immediately after the discovery of electricity - switches, resistors, capacitors, semiconductor devices. Improvement went both in the direction of increasing the complexity of circuits and in the desire to fit a large number of elements in a limited area or in a limited volume. And also to create something universal, long-lasting and omni-useful from all the same circuit primitives.

Timer NE555

The history of the invention of this timer shows that real masterpieces are not always made in the best times for inventors, and often even in completely low-tech conditions. At the age of 33, Hans Camenzind had a dream in addition to his official duties. This is not always to the taste of his superiors, and he had to quit. He came up with his masterpiece while sitting in the garage in 1971, and a year later the eight-legged microcircuit quickly went into production and sale. The scheme is simple and, as it turned out, useful. Perhaps the name, which cannot really be explained, also played an important role in the success: why NE - from the name of the company Signetics? Why 555 - because they liked the five? Timer? - yes, but not like ordinary ones. Those that always just tick non-stop in pulses, but this one can give a very precise time interval, and not in some microseconds familiar in pulse technology, but in a fairly noticeable interval: take and turn on a light bulb for a few seconds.

The circuit, as often happens with all ingenious designs, turned out to be at the intersection of two techniques: pulsed and analog.

Analog - operational amplifiers - amplify the signal to the desired standard (2 at the inputs (two-threshold comparator) and 1 at the output). And in the middle there is a pulse RS trigger, which can both generate pulses (multivibrator) and produce a single pulse of a given length (one-shot).

And everything is very easily regulated - practically, by the ratio of the parameters of two resistors and one capacitance connected to the microcircuit at the inputs, as well as by supplying other signals to the inputs.

Apparently, the circuit has some elusively successful ratio of ease of control and simplicity of design, which, combined with the unexpected variety of operation of the elements, has made it popular for so many years. Because the listed properties, as a result, resulted in a very low cost and applicability in various schemes - both consumer goods and professional ones. They are good for use in children's toys, time relays, combination locks, and spacecraft. And annual sales still amount to billions of units around the world. Moreover, the scheme has undergone virtually no changes over the entire period. For what reason is the word “evolution” in quotation marks under the picture above? Timer 555 is produced by many companies around the world. Domestic analogues of NE555 are also known - the KR1006VI1 microcircuit and its CMOS version KR1441VI1.

Functional diagram and description of the device

Functionally, the timer consists of 5 components. The circuit has more pins than internal blocks, which indicates the possible flexibility of inclusion in various circuit solutions involving this microcircuit.

The input internal voltage divider sets the reference voltages for two comparators - upper and lower. The RS flip-flop receives their signals and generates an output signal, which is sent to the power amplifier. There is also an additional transistor with an external collector, which is used to connect an external timing chain.

The pins of the circuit are located the same way, regardless of the design of the microcircuit

Description of the circuit pins

The datasheet below contains the pins and the signals supplied to them, from which the operation of the microcircuit becomes a little clearer. Although a lot depends on its connection.

Application: connection options for NE555 (or NE555 analogues)

One-shot

Capacitance C and resistor R set the pulse duration t produced by the circuit in response to a signal at the Input input (pin 2). The supply voltage does not affect the duration, but the amplitude of the output signal. When a pulse is issued, the circuit does not perceive a change in the input signal. After a time t, the circuit produces a falling edge of the output signal and returns to its original state, after which it is ready to respond to the input signal again. Thus, it can highlight informative bursts (low level) against the background of noise, since the input signal is generally analog. Can work as an anti-bounce circuit.

Pulse generator (multivibrator)

The multivibrator does not need to apply any signals to the input; it starts working immediately after turning on the power.

Capacitor C, discharged at the beginning, sets the input to a low level, causing the timer to fire, producing a high potential at the output. Its duration is determined by the charging of capacitor C through resistors R1 and R2. Next, C is discharged through R2 and input 7, which determines the duration of the pause on the timer. After this, everything is repeated, and the output produces pulses of the amplitude specified by the supply voltage and durations t 1 and t 2, that is, frequency f

and duty cycle S = T/t 1. The duty cycle in this simplest connection cannot be more than 2, since the pulse time t 1 is always > pause time t 2.

Throughout our lives we count down periods of time that determine certain events in our lives one after another. In general, we cannot do without counting time in our lives. After all, it is by hours and minutes that we distribute our daily routine, and these days add up to weeks, months and years. We can say that without time we would lose some specific meaning in our actions, and even more precisely, chaos would definitely burst into our lives. I won’t even talk about business people who go to meetings every day by the hour...
However, today’s article is not at all about the fantastic realities of the possible shutdown of all the clocks in the world, not even about the hypothetically incredible, but still about the really accessible! After all, if we need it, if what we are used to is so necessary, then why give up what is convenient!? Actually, we will talk about the timer, which is also in some way involved in the distribution of our time. Using a homemade timer is not always convenient to measure time, because today they are available even to a first-grader! Progress has come so far that multifunctional watches can be bought in China for a couple of bucks. However, this is not always a panacea.
Let's say, if you need to start or turn off some electronic device, then it is best to implement this on an electronic timer. It is he who will take on the responsibilities of turning the device on and off, through automatic electronic switching of device control. It is this kind of timer on the NE 555 chip that I will talk about.

NE555 timer circuit

Take a look at the picture. As trivial as it may seem, the NE555 microcircuit in this circuit operates in its normal mode, that is, for its intended purpose. Although in fact it can be used as a multivibrator, as a converter of an analog signal to a digital signal, as a microcircuit that provides power to the load from a light sensor, as a frequency generator, as a modulator for PWM. In general, they haven’t come up with anything with it during its existence, which has already exceeded 45 years. After all, the microcircuit was first released back in 1971...

Now, let’s briefly go over the connection of the microcircuit and the principle of operation of the circuit once again.

After pressing the "reset" button, we reset the potential at the input of the microcircuit, since we essentially ground the input. In this case, the 150 mKF capacitor is discharged. Now, depending on the capacitance connected to pin 6.7 and ground (150 mF), the delay period of the timer will depend. Please note that a number of 500 kOhm and 2.2 mOhm resistors are also connected here, that is, these resistors also participate in the formation of the delay.

You can adjust the delay using a 2.2 M variable resistor (in the diagram it is constant, it can be replaced by itself with a variable one). The time can also be changed by replacing the 150 µF capacitor.

So, if the resistance of the resistor chain is about 1 mOhm, the delay will be about 5 minutes. Accordingly, if you turn the resistor to the maximum and make sure that the capacitor charges as slowly as possible, you can achieve a delay of 10 minutes. Here it must be said that when the timer starts counting, the green LED lights up, but when the timer fires, a negative potential appears at the output and because of this the green LED goes out and the red one lights up. That is, depending on what you need, a timer to turn on or off, you can use the appropriate connection to the red or green LED. The circuit is simple and, if all elements are correctly connected, does not require configuration.

P/S When I found this circuit on the Internet, it also had a connection between pins 2 and 4, but with this connection the circuit did not work!!! Maybe this is a bug of a particular instance, maybe there’s something wrong with me or the moon in the sky that night, but then I broke 4, connected pin 2 to pin 6, this conclusion was made based on other similar circuits on the Internet and everything worked!! !

If it is necessary to control the timer with a power load, you can use the signal after a 330 Ohm resistor. This point is shown with a red and green cross. We use a regular transistor, say KT815, and a relay. The relay can be used at 12 volts. An example of such an implementation of power supply control is given in the article light sensor, see the link above. In this case, it will be possible to turn off and on a powerful load.

Datasheet for NE555 timer

In general, if you want, you can take a look at the nominal parameters and internal structure of the timer, at least in the form of a schematic diagram of operation in blocks. By the way, even in this datasheet there will be a connection diagram. The datasheet is from the ST company, this is a company with a name, which means that it seems that the characteristics here may be overstated. If you take a Chinese analogue, then it is quite possible that the parameters will be slightly different. Please note that this chip may be indexed SA555 or SE555.

Summarizing the timer on the NE555 chip

The circuit presented here, although it operates on 9 volts, can also be powered at 12 volts. This means that such a circuit can be used not only for home projects, but also for a car, when the circuit can be directly connected to the car’s on-board network. Although, to be sure, it is better to put LM 7508 or Krenka at 5-9 volts.
In this case, such a timer can be used to delay turning on or off the camera. It is possible to use a timer for “lazy” direction indicators, for heating the rear window, etc. There really are a lot of options.

It only remains to summarize that the time of analog technology is still passing, because this timer uses expensive capacitors, this is especially true for a timer with a significant delay, when the capacitances will be large. This is both money and dimensions in the timer device. Therefore, if the question becomes acute about production volumes and stability of operation, then even the simplest microcontroller will probably benefit.

The only obstacle is that microcontrollers still need to be able to program and apply knowledge not only of the electrical part, connections, but also languages, programming methods, this is also someone’s time, convenience and, ultimately, money.

Video about the operation of a timer on the NE555 chip

You don't need a controller, they said. Do everything with NE555 timers, they said. Well, I did it - it seems, only to make sure that the result was a design that was stunning in its crushing effect on my fragile psyche.

The review, if this text can be called that, will not be too long. Because it only states my complete and unconditional failure in assembling elementary circuits and demonstrates that at least six out of twenty chips are quite functional.

Also note: it seems that the store recently changed the rules, since now they have a minimum order with free delivery of $6, and if less, then they will charge $1.5 for delivery. When I bought, they only wrote off the purchase price, that is, $0.59, and that’s it.

There are exactly twenty pieces in two blisters. On one side, each blister is wrapped with tape, on the other it is closed with a rubber stopper:

In general, I initially bought timers to make a simple generator to find a short circuit in the wiring - my friends became interested. The essence of the device, if I understand correctly, is that the circuit up to the short circuit is an antenna, the signal from which can be heard with a regular MF/LW receiver.

Where the squeaking stops is approximately where the short circuit occurs. This is what it looks like in practice for a friend in whose footsteps I planned to follow:

But then those familiar with the need decided that they didn’t really need everything. Or they decided something else, but I didn’t insist. And be upset too: you’ve seen how much timers cost (a little more than half a dollar for 20 pieces) - what a disappointment?

Regular DIP8:

Therefore, I decided to have fun in a different way and looked at what they actually made from NE555. And, as it turned out, they do a lot of things. All kinds of alarms, voltage indicators, missing pulse indicators. Overall, I was impressed.

Well, since everyone is describing approximately the same thing, here are a couple of RadioKat links: and. Schemes are in the second.

It is assumed that the popularity of the NE555 is explained by the fact that it is a design that has been proven over the years (more precisely, for 45 years), which is disconcertingly simple to configure and quite accurately complies with the characteristics regardless of the supply voltage, which can be in the range from 4.5V to 16V for the regular version (but there are options). That is, the voltage fluctuates, but the frequency is more stable than not.

In fact, to make the timer work, you need a couple of parts and any suitable power source - very attractive to make some shit without much hassle.

As for me, with a microcontroller there is even less hassle, but in the comments to the story about “Pishchal” I gained and lost peace. I realized that I had to try at least to calm down.

So, the idea was simple - a cat feeding timer. Who, having lost all shame, began to demand food almost every half hour, and after eating three crackers, they left satisfied. According to the veterinarian, this is not very useful (and in our opinion, it is also extremely troublesome), so it was necessary to return their diet to its place. Well, that’s a good idea: feed at least no more than once every five to six hours.

Keeping track of the clock, of course, is not difficult. However, firstly, the situation is complicated by the fact that if during the day feeding by the hour goes on more or less, then at night it is no longer quite so, since one cat has, let’s say, a complex character. Exactly - he goes and scratches the radiator with his claws, and even if I decided not to pay attention to this musical experiment of dubious quality, I feel sorry for the neighbors.

That is, at night you have to get up and time it again, and in a semi-conscious state this is a little difficult.

Secondly, not all cats are so scandalous, so some simply do not come along with that troublemaker. And it turns out that the intervals are different for everyone, but in fairness it would be nice to feed at a set time also those who missed an extraordinary meal.

Therefore, I came up with the idea of ​​​​making a bunch of independent timers for a fixed time - one per cat. And just like this: a cat comes, you give him food, you press the button, the light comes on. Just as the light bulb went out, the cat can be fed again.

As you might guess, this is one of the main options for the timer. It can be called differently: it can be called a monostable, it can be called a monostable, it can be called a standby multivibrator.

This does not change the essence: the NE555 is required, in fact, to issue only one pulse of the required duration.

Therefore, I took the timer circuit from:

But I simplified it a little by getting rid of the trimming resistor (since I have a fixed interval) and the second LED - as unnecessary. At the same time, I changed the values ​​of the timing chain, checking with the same documentation, which reports that to calculate the approximate pulse duration, you should use the formula y t = 1.1RC.

Having played with the fonts and the values ​​of the parts available in the Chip-i-Dip boutique, I found that for a five-hour interval that suits everyone, a capacitor with a capacity of 3300 μF and a resistor of 5.1 MΩ are quite suitable:

T = 1.1*0.0033*5100000 = 18513 sec = 5.14 hours.

The reality, however, turned out to be slightly different from the theory. The timer, assembled according to this scheme and with these values, continued to work after five hours. I didn't have the patience to wait for it to finish working, so I assumed that the NE555 doesn't work very well with large denominations.

A quick googling showed that yes, it is possible, but there should be no problems (theoretically) with a resistance of up to 20 MOhm at a supply voltage of 15 V. Therefore, I continued experimenting and found out that in my case the formula turns out something like this:

And I was very grateful to myself that I bought not only 5.1 MOhm, but also, just in case, the closest ratings - 4.7 MOhm and 3.9 MOhm. The latter, fortunately, was just right for the required interval.

With these ratings (3300 µF and 3.9 MOhm) I assembled a block of timers with lights and buttons. I connected everything with a common power line; they have no other points of contact (well, at least I tried not to). And since I was assembling the canopy, I checked myself at every step with a multimeter and was almost calm when I started the first of the timers.

It turned out like this (I warned you at the very beginning):

It turned on as expected, so I unsoldered the remaining buttons and lights and turned it on. I pressed buttons. The LEDs turned on exactly as they were supposed to: you press the button - it turns on, and that's it.

And then I made a big mistake. I didn’t do a few more test runs, but was just upset that I didn’t solder the wires to the buttons very well, and decided to resolder them. Therefore, I don’t yet know what exactly happened: either I did something wrong initially, or I managed to ruin something while resoldering the wires.

But it turned out funny. When turned on again (with the wires soldered), three LEDs immediately lit up. And pressing the buttons revealed complete chaos: you press one button - its LED lights up (i.e., in theory, the timer turns on), you press another - the first LED goes out, the second lights up. And so on.

I found out empirically that there is a certain combination of button presses that lights up all the LEDs. But so far I haven’t gotten around to checking the circuit for short circuits where there shouldn’t be any.

Bonus track - let's play minesweeper:

To summarize, I want to say that I had fun with timers. In practice, I checked that you can buy them in China - workers come.

And although I couldn’t make the cat timer, I got the “Light all the light bulbs” puzzle as a bonus. And at the same time the understanding that NE555 is clearly not for me. And that's why:

Minimum supply voltage 4.5V
- high current consumption

Of course, these shortcomings can be overcome by ordering the CMOS version of the chip, which is much more economical and works starting at 1.5V. But regular ones cost $0.59 for twenty pieces, and CMOS ones cost about $10. That is, the controller is approximately twice as expensive, and if two or more timers are used in the design, the benefit disappears altogether.

So thank you everyone, I’m returning to the ATmega328p, on which, obviously, I will make a feeding timer.

Ps. And now can I also write about the screen from ITEAD Studio? By the way, my conscience is tormenting me, because, on the one hand, these screens here were already through the roof, and on the other hand, we must fulfill the promise.