Chip timer NE555 amateur radio designs

Every radio amateur has met with the NE555 chip more than once. This little eight-legged timer has gained immense popularity for its functionality, practicality and ease of use. On the 555 timer, you can assemble circuits of the most varied levels of complexity: from a simple Schmitt trigger, with just a couple of elements, to a multi-stage combination lock using a large number of additional components.

In this article, we will take a closer look at the NE555 microcircuit, which, despite its considerable age, is still in demand. It should be noted that, first of all, this demand is due to the use of ICs in circuitry using LEDs.

Description and scope

NE555 is the development of the American company Signetics, whose specialists did not give up in the conditions of the economic crisis and were able to implement the works of Hans Camenzind. It was he who, in 1970, was able to prove the importance of his invention, which at that time had no analogues. The NE555 IC had a high packing density at a low cost, which earned it a special status.

Subsequently, competing manufacturers from around the world began to copy it. This is how the domestic KR1006VI1 appeared, which remained unique in this family. The fact is that in KR1006VI1 the stop input (6) has priority over the start input (2). In the imported counterparts of other firms, this feature is absent. This fact should be taken into account when developing circuits with the active use of two inputs.

However, in most cases, priorities do not affect device performance. In order to reduce power consumption, back in the 70s of the last century, the release of a CMOS-series timer was launched. In Russia, the field-effect transistor microcircuit was named KR1441VI1.

The 555 timer is most widely used in the construction of generator circuits and time relays with the possibility of delay from microseconds to several hours. In more complex devices, it performs the functions of eliminating contact bounce, PWM, digital signal recovery, and so on.

Features and disadvantages

The timer features an internal voltage divider that sets a fixed upper and lower threshold for the two comparators. Since the voltage divider cannot be eliminated and the threshold voltage cannot be controlled, the scope of the NE555 is narrowed.

Timers assembled on CMOS transistors are devoid of the listed disadvantages and do not need to install external capacitors.

The main parameters of the IC series 555

The interior of the NE555 includes five functional units, which can be seen in the logic diagram. A resistive voltage divider is located at the input, which provides two reference voltages for precision comparators. The output contacts of the comparators go to the next block - an RS-flip-flop with an external output for reset, and then to the power amplifier. The last node is an open collector transistor, which can perform several functions, depending on the task at hand.

The recommended supply voltage for IC types NA, NE, SA lies in the range from 4.5 to 16 volts, and for SE it can reach 18V. In this case, the current consumption at the minimum Usup is equal to 2-5 mA, with the maximum Usup - 10-15 mA. Some 555 CMOS-series ICs consume less than 1 mA. The highest output current of the imported microcircuit can reach 200 mA. For KR1006VI1, it is not higher than 100 mA.

Build quality and manufacturer greatly affect the operating conditions of the timer. For example, the operating temperature range of the NE555 is 0 to 70 ° C and the SE555 is -55 to + 125 ° C, which is important to know when designing devices for operation in an open environment. For more details on the electrical parameters, you can find out the typical values \u200b\u200bof voltage and current at the inputs CONT, RESET, THRES, and TRIG in the datasheet on the XX555 series IC.

Location and purpose of pins

NE555 and its analogs are predominantly available in eight-pin PDIP8, TSSOP or SOIC packages. The pin layout is standard regardless of the case. The conventional graphic designation of the timer is a rectangle with the inscription G1 (for a single pulse generator) and GN (for multivibrators).

1. Common (GND). First conclusion regarding the key. It is connected to the minus of the device power supply.
2. Trigger (TRIG). Applying a low-level pulse to the input of the second comparator leads to the triggering and appearance of a high-level signal at the output, the duration of which depends on the nominal value of the external elements R and C. The possible variations of the input signal are described in the "One-vibrator" section.
3. Output (OUT). The high level of the output signal is (Upit-1.5V), and the low level is about 0.25V. Switching takes about 0.1 μs.
4. Reset (RESET). This input has the highest priority and is able to control the timer operation regardless of the voltage on the other pins. To enable the launch, it is necessary that a potential of more than 0.7 volts is present on it. For this reason, it is connected through a resistor to the circuit power supply. The appearance of a pulse of less than 0.7 volts inhibits the operation of the NE555.
5. Control (CTRL). As can be seen from the internal device of the IC, it is directly connected to the voltage divider and, in the absence of external influences, gives out 2/3 Usup. By applying a control signal to CTRL, you can get a modulated signal at the output. In simple circuits, it connects to an external capacitor.
6. Stop (THR). It is the input of the first comparator, the appearance of a voltage at which more than 2 / 3Upit stops the trigger and drives the timer output to a low level. In this case, there should be no trigger signal on pin 2, since TRIG has priority over THR (except for KR1006VI1).
7. Discharge (DIS). It is connected directly to the internal transistor, which is connected in a common collector circuit. Usually, a timing capacitor is connected to the collector-emitter junction, which is discharged while the transistor is in the open state. Less commonly used to increase the load capacity of the timer.
8. Power supply (VCC). It is connected to the plus of the 4.5-16V power supply.

Operating modes NE555

The 555 series timer operates in one of three modes, let's consider them in more detail using the NE555 chip as an example.

One vibrator

The schematic diagram of the one-shot is shown in the figure. To form single pulses, in addition to the NE555 microcircuit, you will need a resistance and a polar capacitor. The scheme works as follows. A single low-level pulse is applied to the timer input (2), which causes the microcircuit to switch and a high signal level appears at the output (3). The signal duration is calculated in seconds using the formula:

After a specified time (t), a low-level signal (initial state) is generated at the output. By default, pin 4 is combined with pin 8, that is, it has a high potential.

During the development of circuits, you need to take into account 2 nuances:

1. The power supply voltage does not affect the pulse duration. The higher the supply voltage, the higher the charging rate of the timing capacitor and the greater the amplitude of the output signal.
2. An additional pulse, which can be applied to the input after the main one, will not affect the timer until the time t expires.

The operation of the single pulse generator can be influenced externally in two ways:

• send a low-level signal to Reset, which will reset the timer to its original state;
• as long as input 2 is low, the output will remain high.

Thus, with the help of single signals at the input and the parameters of the timing chain, it is possible to obtain at the output rectangular pulses with a clearly specified duration.

Multivibrator

The multivibrator is a generator of periodic rectangular pulses with a given amplitude, duration or frequency, depending on the task at hand. Its difference from a one-shot device is that there is no external disturbance for the normal functioning of the device. A schematic diagram of a multivibrator based on NE555 is shown in the figure.

Resistors R 1, R 2 and a capacitor C 1 are involved in the formation of repetitive pulses. Pulse time (t 1), pause time (t 2), period (T) and frequency (f) are calculated using the formulas below: From these formulas, it is easy to notice that the pause time cannot exceed the pulse time, that is, it will not be possible to achieve a duty cycle (S \u003d T / t 1) of more than 2 units. To solve the problem, a diode is added to the circuit, the cathode of which is connected to terminal 6, and the anode to terminal 7.

In the datasheet, microcircuits are often operated with the value of the inverse duty cycle - Duty cycle (D \u003d 1 / S), which is displayed as a percentage.

The scheme works as follows. At the moment of power supply, the capacitor C 1 is discharged, which transfers the timer output to a high level. Then C 1 starts charging, gaining capacity to the upper threshold value 2/3 U PIT. Having reached the threshold, the IC switches, and a low signal level appears at the output. The process of discharge of the capacitor (t 1) begins, which continues to the lower threshold value 1/3 U PIT. Upon reaching it, a reverse switching occurs, and a high signal level is set at the output of the timer. As a result, the circuit goes into a self-oscillating mode.

Precision Schmitt trigger with RS trigger

A two-threshold comparator and an RS flip-flop are built inside the NE555 timer, which makes it possible to implement a precision Schmitt trigger with an RS flip-flop at the hardware level. The input voltage is divided by the comparator into three parts, when each of them is reached, the next switching occurs. In this case, the value of the hysteresis (reverse switching) is equal to 1/3 U PIT. The possibility of using NE555 as a precision trigger is in demand in the construction of automatic control systems.

3 most popular NE555 based circuits

One vibrator

A practical version of the TTL NE555 single shot circuit is shown in the figure. The circuit is powered by a unipolar voltage from 5 to 15V. The timing elements here are: a resistor R 1 - 200kOhm-0.125W and an electrolytic capacitor C 1 - 4.7mkF-16V. R 2 maintains a high potential at the input until some external device drops it to a low level (for example, a transistor switch). Capacitor C 2 protects the circuit from through currents at the moments of switching.

The activation of the single-shot occurs at the moment of a short-term ground fault of the input contact. In this case, a high level is formed at the output with the duration:

t \u003d 1.1 * R 1 * C 1 \u003d 1.1 * 200000 * 0.0000047 \u003d 1.03 s.

Thus, this circuit forms a delay of the output signal relative to the input one by 1 second.

Flashing LED on the multivibrator

Based on the multivibrator circuit discussed above, you can assemble a simple LED flasher. To do this, an LED is connected to the output of the timer in series with the resistor. The resistor value is found by the formula:

R \u003d (U OUT -U LED) / I LED,

U OUT - the amplitude value of the voltage at terminal 3 of the timer.

The number of connected LEDs depends on the type of NE555 chip used, its load capacity (CMOS or TTL). If it is necessary to blink an LED with a power of more than 0.5 W, then the circuit is supplemented with a transistor, the load of which will be the LED.

Time relay

An adjustable timer circuit (electronic time relay) is shown in the figure.
With its help, you can manually set the duration of the output signal from 1 to 25 seconds. To do this, in series with a constant resistor of 10 kΩ, a variable with a nominal value of 250 kΩ is set. The capacity of the timing capacitor is increased to 100 μF.

The scheme works as follows. Initially, pin 2 is high (from the power supply) and pin 3 is low. Transistors VT1, VT2 are closed. At the moment a positive pulse is applied to the base VT1, current flows through the circuit (Vcc-R2-collector-emitter-common wire). VT1 opens and puts NE555 into timing mode. At the same time, a positive pulse appears at the output of the IC, which opens VT2. As a result, the emitter current VT2 triggers the relay. The user can interrupt the task at any time by short-circuiting RESET to ground.

The SS8050 transistors shown in the diagram can be replaced with KT3102.

It is impossible to consider all popular schemes based on NE555 in one article. For this, there are whole collections, which contain practical developments for the entire existence of the timer. We hope that the information provided will serve as a guide during the assembly of circuits, including the load of which are LEDs.

Read the same

555 chips are used quite often in amateur radio practice - they are practical, multifunctional and very easy to use. On such microcircuits, you can implement any design - both the simplest Schmitt triggers with a couple of additional elements, and multi-stage combination locks.

NE555 was developed quite a long time ago, even in the Soviet magazines "Radio", "Modelist-Constructor", on the analogs of this microcircuit one could find many homemade products. Today this microcircuit is actively used in designs with LEDs.

Chip Description

This is the development of the US company Signetics. It was its specialists who were able to put into practice the work of Camenzind Hans. This, one might say, is the father of an integrated microcircuit - in difficult conditions of high competition, engineers managed to make a product that entered the world market and gained wide popularity.

In those years, the 555 series microcircuit had no analogues in the world - a very high density of assembly of elements in the device and an extremely low cost price. It is thanks to these parameters that it has earned high popularity among designers.

Domestic analogues

After that, the massive copying of this radio element began - the Soviet analogue of the microcircuit was called KR1006VI1. By the way, it is in every respect a unique development, even though it has many analogues. Only for domestic microcircuits the stop input has a higher priority than the start input. None of the foreign designs has such a feature. But this feature must be taken into account when designing circuits in which both inputs are actively used.

Where is it applied?

But it should be noted that the priorities of the inputs do not greatly affect the performance of the microcircuit. This is just a small nuance that should be taken into account in rare cases. To reduce power consumption, the production of CMOS elements was launched in the mid-70s. In the USSR, microcircuits on field workers were called KR1441VI1.

Generators on the 555 chip are very often used in the designs of radio amateurs. It is not difficult to implement a time relay on this microcircuit, and the delay can be set from a few milliseconds to hours. There are also more complex elements, which are based on the 555 circuit - they contain devices for preventing contact rattling, PWM controllers, restoring a digital type signal.

Advantages and disadvantages of the microcircuit

There is a built-in voltage divider inside the timer - it is he who allows you to set a strictly fixed lower and upper threshold at which the comparators are triggered. It is from this that we can draw a conclusion about the main drawback - the threshold values \u200b\u200bcannot be controlled, and the divider cannot be excluded from the design, the area of \u200b\u200bpractical application of the 555 microcircuit is significantly narrowed. Multivibrator and one-shot circuits can be built, but more complex designs will not work.

How to get rid of the flaws?

But you can get rid of such a problem, it is enough to install a polar capacitor of no more than 0.1 μF between the control output and the power supply minus.

And in order to significantly increase the noise immunity, a non-polar capacitor with a capacity of 1 μF is installed in the power circuit. In the practical application of 555 microcircuits, it is important to consider whether passive elements - resistors and capacitors - affect their operation. But one feature should be noted - when using timers on CMOS elements, all these disadvantages simply go away, there is no need to use additional capacitors.

Main parameters of microcircuits

If you decide to make a timer on a 555 chip, then you need to know its main features. In total, the device has five nodes, they can be seen in the diagram. A resistive voltage divider is located at the input. With its help, two reference voltages are formed, which are necessary for the operation of the comparators. Comparator outputs are connected to an RS flip-flop and an external reset pin. And only after that to the amplifying device, where the signal value increases.

Power supply of microcircuits

At the end there is a transistor with an open collector - it performs a number of functions, everything depends on what specific task it faces. It is recommended to supply a supply voltage in the range of 4.5-16 V to integrated circuits NE, SA, NA. Only for in the case of using 555 microcircuits with the SE abbreviation, an increase to 18 V.

The maximum current consumption at a voltage of 4.5 V can reach 10-15 mA, the minimum value is 2-5 mA. There are CMOS microcircuits in which the current consumption does not exceed 1 mA. For domestic ICs of the KR1006VI1 type, the current consumption does not exceed 100 mA. A detailed description of the 555 chip and its domestic counterparts can be found in the datasheet.

Operation of the microcircuit

The operating conditions depend directly on which company produces the microcircuit. As an example, there are two analogs - NE555 and SE555. In the first, the temperature range in which it will normally work is in the range of 0-70 degrees. In the second, it is much wider - from -55 to +125 degrees. Therefore, such parameters must always be taken into account when designing devices. It is advisable to familiarize yourself with all the typical values \u200b\u200bof voltages and currents at the Reset, TRIG, THRES, CONT pins. To do this, you can use a datasheet for a specific model - in it you will find comprehensive information.

The practical application of the scheme depends on this. Radio amateurs use the 555 chip quite often - in control systems there are even master oscillators for radio transmitters on this element. Its advantage over any transistor or tube version is its incredibly high frequency stability. And there is no need to select elements with high stability, to install additional devices for voltage equalization. It is enough to install a simple microcircuit and amplify the signal that will be generated at the output.

IC pin assignment

On the 555 series microcircuits there are only eight pins, the type of package is PDIP8, SOIC, TSSOP. But in all cases, the purpose of the conclusions is the same. The UGO element is a rectangle labeled "G1" for a single pulse generator and "GN" for a multivibrator. Pin assignment:

1. GND - common, in order it is the first (if you count from the key-tag). This pin is supplied with minus from the power supply.
2. TRIG - trigger input. It is to this pin that a low-level pulse is fed and it goes to the second comparator. As a result, the IC starts up and a high-level signal appears at the output. Moreover, the signal duration depends on the values \u200b\u200bof C and R.
3. OUT - the output at which the high and low level signals appear. Switching between them takes no more than 0.1 μs.
4. RESET - reset. This input has the highest priority, it controls the timer, and it does not depend on whether there is voltage on the other legs of the microcircuit. To enable starting, a voltage of over 0.7V is required. In the event that the pulse is less than 0.7V, then the operation of the 555 microcircuit is prohibited.
5. CTRL is a control input that connects to a voltage divider. And if there are no external factors that can affect the operation, 2/3 of the supply voltage is output at this output. When a control signal is applied to this input, a modulated pulse is generated at the output. In the case of simple circuits, this output is connected to a capacitor.
6. THR - stop. This is the input of the 1st comparator, if a voltage of 2/3 of the supply voltage appears on it, the trigger stops and the timer is set to a low level. But a prerequisite is that there should be no trigger signal on the TRIG leg (since it has priority).
7. DIS - discharge. It connects directly to a transistor inside the 555 chip. It has a common collector. A capacitor is installed in the emitter-collector circuit, which is necessary in order to set the time.
8. VCC - connection to the plus of the power supply.

Single shot mode

In total, there are three modes of the NE555 microcircuit, one of them is a one-shot. To implement the pulse shaping, it is necessary to use a polar-type capacitor and a resistor.

The circuit works like this:

1. Voltage is applied to the timer input - a low-level pulse.
2. The operating mode of the microcircuit is switched.
3. A high signal appears at pin 3.

After this time, a low-level signal will be formed at the output. In the multivibrator mode, pins "4" and "8" are connected. When developing circuits based on a one-shot, you need to take into account the following nuances:

1. The supply voltage cannot influence the pulse time. With increasing voltage, the charging rate of the capacitor, which sets the time, is faster. Consequently, the output signal amplitude increases.
2. If an additional pulse is applied to the input (after the main one), it will not affect the timer's performance until the end of time t.

To influence the functioning of the generator, you can use one of the following methods:

1. Apply a low-level signal to the RESET pin. This will return the timer to its default state.
2. If a low-level signal goes to input "2", then the output will always have a high pulse.

With the help of single pulses applied to the input, and changing the parameters of the timing components, it is possible to obtain a square-wave signal of the required duration at the output.

Multivibrator circuit

Any novice radio amateur can make a metal detector on a 555 microcircuit, but for this you need to study the features of the operation of this device. A multivibrator is a special generator that produces rectangular pulses at a certain frequency. Moreover, the amplitude, duration and frequency are strictly set - the values \u200b\u200bdepend on the task facing the device.

Resistors and capacitors are used to generate repetitive signals. The signal duration t1, pauses t2, frequency f, and period T can be found using the following formulas:

• t1 \u003d ln2 * (R1 + R2) * C \u003d 0.693 * (R1 + R2) * C;
• t2 \u003d 0.693 * C * (R1 + 2 * R2);
• T \u003d 0.693 * C * (R1 + 2 * R2);
• f \u003d 1 / (0.693 * C * (R1 + 2 * R2)).

Based on these expressions, you can see that the pause duration should not be longer than the signal time. In other words, the duty cycle will never exceed 2. The practical application of the 555 microcircuit directly depends on this. Circuits of various devices and structures are built according to datasheets - instructions. They provide all possible recommendations for assembling devices. The duty cycle can be found by the formula S \u003d T / t1. To increase this figure, it is necessary to add a semiconductor diode to the circuit. Its cathode connects to the sixth leg, and the anode to the seventh.

If you look at the datasheet, then the reciprocal of the duty cycle is indicated in it - it can be calculated using the formula D \u003d 1 / S. It is measured as a percentage. The operation of the multivibrator circuit can be described as follows:

1. The capacitor is completely discharged when power is applied.
2. The timer is put into a high-level state.
3. The capacitor accumulates a charge and the voltage across it reaches a maximum - 2/3 of the supply voltage.
4. The microcircuit switches and a low-level signal appears at the output.
5. The capacitor is discharged during t1 to the level of 1/3 of the supply voltage.
6. The 555 chip switches again and a high-level signal is generated at the output again.

This mode of operation is called self-oscillating. The signal value is constantly changing at the output, the 555 timer chip is in different modes for equal periods of time.

Precision Schmitt Trigger

Timers such as NE555 and similar have a built-in comparator with two thresholds - lower and upper. In addition, it has a special RS-trigger. This is what makes it possible to implement the design of the precision Schmitt trigger. The voltage supplied to the input is divided by a comparator into three equal parts. And as soon as the level of the threshold value is reached, the operating mode of the microcircuit is switched. In this case, the hysteresis increases, its value reaches 1/3 of the supply voltage. A precision trigger is used in the design of automatic control systems.

NE555 is a legendary timer IC, which was one of the first integrated micro-assemblies. It carries about 20 transistors and is used to operate in two modes. In the mode of the timer and square-wave generator directly.

555 Timer Reference Documentation

Fill in one of the values \u200b\u200bbelow and click the Calculate button and the calculator will give you a number of possible options for the resistances of resistors R1, R2 & the value of the capacitor.

Directory - pinout with a detailed description of all pins of the 555 series timer microcircuit

Moreover, the volume level depends on the amount of light falling on the photosensitive resistor

The operation of the circuit is not at all complicated, the NE555 timers are two generators, a low-frequency generator (the first on the left in the diagram) controls the operation of the second high-frequency generator (decreasing and increasing the generation frequency), then the pulses follow to the transistor amplifier VT1, to the emitter of which an eight-ohm speaker is connected.

At the moment when the piezoelectric sensor detects a mechanical effect, it generates an electrical pulse, which is a signal to start a monostable multivibrator, the output of which is connected to a dual optocoupler.

This light alarm circuit is triggered when the light level of the sensor drops sharply, triggering an audible alarm. The device does not work when the brightness changes smoothly. To increase the battery life, the audible alarm sounds from one to ten seconds, the sounding time can be adjusted using the R5 trimming resistance.

The basis of the stroboscope circuit are timer devices assembled on KR1006VI1 microcircuits (domestic analogue of the 555 series) which have more stable time characteristics, since the pulse duration and pause between pulses do not depend on the power supply voltage.

A very good way to control the brightness of the LEDs is to use pulse-width modulation, because the LEDs are powered by the recommended current and it is possible to adjust the brightness of the glow by supplying power at a higher frequency. The change in period is directly proportional to brightness.

For acoustic signaling, sounds that resemble a siren are often used. They are obtained electromechanically or electronically. The proposed electronic alarm device has the advantage that the tone of the siren sound can be changed. It consists of a master oscillator, modulator and amplifier. The master oscillator is made on an integrated circuit B555D (see schematic diagram). The desired tone is selected using the resistor R4. The frequency of the generator, equal to 1 kHz, is set by the resistor R6 and the capacitor C4. The howling sound of a siren is obtained by feeding a sinusoidal signal with a frequency of approximately 1 Hz from a generator on a transistor VT1. to pin 5 of the microcircuit. Thanks to the VD1 diode and the input resistance of the microcircuit, equal to 5 kOhm, the electrical oscillations generated by the master oscillator are modulated with a frequency of 1 Hz.

All our life we \u200b\u200bcount the time intervals that one after another determine certain events in our life. In general, we cannot do without timing in our life. 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 have lost some definite meaning in our actions, or more precisely, chaos would definitely burst into our life. I’m not even going to talk about business people who go to meetings every day by the clock ...
However, today's article is not at all about the fantastic realities of the possible shutdown of all clocks in the world, not even about the hypothetically incredible, but still about the really accessible! After all, if we need, if what we are accustomed to is so necessary, why should we abandon the convenient !? Actually, we will just talk about the timer, which also in some way participates in the distribution of our time. Using a homemade timer is not always convenient to measure time, because today they are available even to first graders! Progress has gone so far that a multifunction watch can be bought in China for a couple of bucks. However, this is not always a panacea.
For example, if it is necessary to start or disable some electronic device, then it is best to implement this on an electronic timer. It is he who will take on the responsibility for turning the device on and off, by automatic electronic switching of device control. It is about such a timer on the NE 555 chip that I will tell you about.

Timer circuit on the NE555 chip

Take a look at the picture. As it may seem trite, but the NE555 microcircuit works in this circuit in its normal mode, that is, for its intended purpose. Although in fact it can be used as a multivibrator, as an analog-to-digital signal converter, as a microcircuit that provides power to the load from a light sensor, as a frequency generator, as a modulator for PWM. In general, what has not been invented with him during its existence, which has already exceeded 45 years. After all, a microcircuit came out for the first time back in 1971 ...

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

After pressing the "reset" button, we zero 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 the 6.7 leg and the ground (150 mKF), the timer delay-exposure period will depend. Note that a number of 500 kΩ and 2.2 mΩ resistors are also connected here, that is, these resistors are also involved in the formation of the delay-delay.

The delay can be adjusted using a 2.2 M variable resistor (in the diagram it is constant, it can be replaced by itself with a variable). Also, the time can be changed by replacing the 150 uF capacitor.

So if the resistance of the chain of resistors is about 1 mΩ, the delay will be about 5 minutes. Accordingly, if you unscrew the resistor to the maximum and make the capacitor charge as slowly as possible, then you can achieve a delay of 10 minutes. Here I must say that when the timer starts counting down, the green LED lights up, when the timer is triggered, a negative potential appears on 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 scheme is simple and, if all the elements are correctly connected, it does not need to be configured.

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

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

Datasheet for NE555 timer

In general, if you want, you can take a look at the nominal parameters and the internal device of the timer, at least in the form of a schematic diagram of work in blocks. By the way, even in this datasheet, the connection diagram will be given. Datasheet from ST company, this is a company with a name, which means that it is thought that the characteristics here may be overestimated. If you take the Chinese counterpart, then it is quite possible the parameters will be slightly different. Please note that this microcircuit can be with the index SA555 or SE555.

Summing up the timer on the NE555 chip

The circuit shown here, although it works from 9 volts, is quite capable of being powered by 12 volts. This means that such a scheme can be used not only for home projects, but also for a car, when the circuit can be directly connected to the vehicle's on-board network. Although for fidelity it is better to put LM 7508 or KRENKA for 5-9 volts.
In this case, such a timer can be used to delay turning on the camera or turning it off. It is possible to use a timer for "lazy" direction indicators, for heating the rear window, etc. There are really many options.

It remains only to summarize that the time of analog technology is still passing, because expensive capacitors are used in this timer, this is especially true for a timer with a significant delay, when the capacities are large. This is both money and dimensions in the timer device. Therefore, if the question is acute about the volume of production, about the stability of work, then, perhaps, even the simplest microcontroller will win.

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 timer on the NE555 chip

It should be noted right away when describing the NE 555 microcircuit that it is produced in both standard TTL logic and CMOS, so it can operate in a wide voltage range and is used in many types of devices as a clock pulse generator or a universal timer. The microcircuit can generate both single and repetitive pulses, which depends on the switching circuit and the choice of a specific operating mode.

The first version of the IP was developed back in 1971 by the then famous Signetics company. In terms of its characteristics and functionality, it is widely demanded, as evidenced by its active use in devices for controlling the speed of rotation of motors and thyristor power controllers.

Also, it can be used to design a unified pulse generator with a variable output frequency of a pulse train. For a detailed description characteristics of the microcircuit look at the ne 555 datasheet. It lists not only the main characteristics, but also presents diagrams of work. And in this description ne 555 we will provide general information sufficient for the development of electronic devices with your own hands.

Background of IP creation

In the 70s. Signetics fell under the influence of the crisis and was forced to cut its staff by at least 50%, including the developer of the presented scheme. Therefore she was created literally on his knees in a garage, and the NE 566 developed by him was taken as a basis. The platform of the future IC already consisted of the main functional blocks necessary for the operation:

There are different types of switching circuits on the ne 555 for the operation of the microcircuit, it was enough to have an external RC circuit, which was a timing circuit. And inner voltage divider, in proportion to which the amplitude of the output signal was formed. After some time and making minor improvements, in particular, replacing the built-in stable current generator to charge the internal capacitor with a resistor, it entered the series.

As for the timer structure, it contained:

• 23 transistors;
• 16 resistors;
• 2 diodes.

Microcircuit analogs

The universal timer soon acquired functional analogs, which became Soviet microcircuits from the KR series:

• 1006VI1;
• 1008VI1;
• 1087VI2;
• 1087VI3.

Also, the ne555 microcircuit has an analogue, for example, KR10006VI1, then it is worth considering the fact that the reset input R has priority over the installation. This the moment is somehow missed in the technical description of the MS, which is an important fact in the construction of electronic circuits. In other microcircuits, pins take precedence up to the opposite S over R.

All of the above presented analogs of timers are based on standard TTL logic. If you want to design ne555 devices with more economical performance, then it is better to use an MS from the CMOS series. These are the devices:

• ICM 7555 IPA;
• GLC 555;
• KR1441VI1.

Chip characteristics

The functional diagram of the presented microcircuit is quite simple and consists of the following blocks:

• a voltage divider that compares the input signal with two reference levels;
• 2 high-precision comparators for high and low signal levels;
• trigger with built-in RS-inputs and additional reset, medium power output transistor bipolar or field effect depending on technology.

Also, in hardware, a power amplifier is provided in the design of the microcircuit, which increases the load capacity of the device and its quality of work.

The microcircuit is universal, no matter how you look, from all sides. For example, the basic version NE 555 is designed on supply voltage in the range from 4.5 to 16.5 V, which greatly simplifies the process of designing many circuits, since there is no need to adhere to a specific power supply.

But if it is necessary to power the pulse generator from a reduced level of the order of 2-3 V, then it is better to use circuits based on CMOS logic. They not only can to function freely at low voltage, but also have increased resistance to interference and power instability.

Also, modifications of devices with an increased threshold of the supply voltage, which can reach 18 V, are produced. These MCs can be used in pulse devices and generators.

According to the information provided by the western on the ne555 datasheet, the current consumed by the device depends on the magnitude of the input pulse. If it lies at a nominal level of about 5 V, then current magnitude is no more than 6 mA. But if the voltage rises to 15V, then the current also rises to 15mA. Usually, devices are developed with their own hands for an average current rate, which leaves about 10 mA, which indicates a supply voltage in the range from 9 to 12 V. But this is typical for TTL logic.

Microcircuits based on CMOS transistors consume even less - 100-200 μA, which makes them even more economical. But the maximum value of the consumed current does not exceed 100 mA. If it takes more than this value from you, it means that the device is defective and requires replacement.

Some problems and features of working with a microcircuit

An 8-pin package is a good idea, but this form factor makes it difficult to work with the timer. Namely, it is deprived of the ability to independently compare the signals of the upper and lower thresholds, which quite often required in conversion devices, for example, the same ADC. To realize this opportunity, radio amateurs resort to using a different series of devices, for example, NE 521, or install 3I-NOT elements at the input, if appropriate.

In bipolar devices, there is such a drawback as a pulse current when turning on and off, the value of which can reach 400 mA, which can cause a breakdown output transistor or other elements of the circuit into which it was soldered. The reason for this phenomenon is the through-current of the output stage, which occurs due to the same high pulses on the power supply.

To eliminate the problem, it is recommended to use a special blocking capacitor connected to inputs 5 and a common (power supply min) with a capacity of about 0.01–0.1 μF. Due to the charge of its plates, the internal voltage in the MC, input to the output stage, is smoothed, which excludes the possibility of breakdown. It also protects the internal divider from external interference that can cause false alarms.

Also, as is the case with many other TTL-logic microcircuits, it is recommended to bypass NE 555 with a quenching capacitor with ceramic plates with a capacity of 1 μF.

Purpose and arrangement of microcircuit pins

The basic version of NE 555 has an 8-pin DIP package, but other modifications are also available that are analogs. Therefore, orient exclusively of this description when building devices with your own hands, it is not worth it. For each microcircuit, you need to view your datasheet.

The schematic designation of the device is displayed in the form of the inscription "G 1 / GN". In foreign reference books, this inscription can be deciphered as a generator of single and series of pulses. what regarding pinout and their purpose, then all the same type of MS are standardized and can be interchangeable without making any modifications.

The table below shows the pinouts in a standard MS package:

Modes of operation and application of the microcircuit

The simplest circuit implementation used in various digital devices is a one-shot. On the example of this circuit, you can also see a typical connection using a quenching and shunt capacitors. It is in this design that this microcircuit is most often used. And it works as follows:

Upon arrival of a signal with a low level at the MS input at number 2, the timer starts to work in the time counting mode. In this case, a high level is set at the output of the device throughout the entire duration of the time interval... This time can be set independently by choosing the necessary external components, which are a resistor and a capacitor, connected to the plus of the power supply and pin number 6.

The time delay is determined using the standard formula, taking into account the correction constant: t \u003d 1.1 RC. At the end of the counting (capacitor discharge), the timer returns to its original state. And the output signal is reversed. So until the next arrival of the low-level input pulse.

Moreover, if there is a low level at the input, then the output is high. And when a pulse is applied to the reset input of the trigger, the timer stops counting and the signal level at the output changes to the opposite.

Independent generator mode

To turn on the microcircuit in multivibrator mode, there is a circuit shown in the figure below. Here everything is as simple as in the previous version, but there are some peculiarities of calculating the element and characteristics of the output signal sequence. To set a specific frequency change the output signal and the subsequent switching to the opposite stable state, it will be necessary to combine pins 2 and 6 and set another resistor in the divide, reducing the capacitor charge current, but at the same time connecting the input signal with the trigger setting input. And to calculate the parameters used by the element, you will need to use the following simple calculation formulas:

Change in the duty cycle of the output pulse

Often it is required to use a 555 chip with the ability to set the duty cycle of the output signal. For example, to make it larger than 2, then this will require an additional chain between 7 and 6 pinsby connecting a diode to them. In this case, the anode terminal contacts with terminal 7 of the MC. Such inclusion of an additional component shunts the resistor R 2, providing the capacitor charging circuit through R 1. Then, when calculating the duration of the high signal level at the output, it will take place according to the formula without taking into account R 2.

In reverse loop discharge current will flow through R 2, and R 1 is no longer involved in the process. And it is determined by the formula that was indicated above without changes.