What is a tonometer, its types, functions. Structural diagram and description of individual components

Blood pressure is one of key indicators human health. If it often rises, then this is already a disease, and a large excess of the norm is life-threatening. Almost half of humanity suffers from hypertension - it is required to constantly control the pressure. That is why it is so important to have a blood pressure monitor handy. We will figure out what types of blood pressure monitors are convenient to use and how to choose the best and most inexpensive.

What tonometers are

A tonometer is a special device for measuring blood pressure. Indicators are displayed immediately and give full information about blood pressure and heart rate. Any deviations from the norm are manifested by unpleasant symptoms: headache, nausea, dizziness.

The modern market pleases with various devices for measuring the indicators in question. They differ in the set of functions performed, the accuracy of the readings, dimensions and cost.

There are two types of devices: mechanical and electronic. The first are divided into semi-automatic and automatic. Fully automated devices are divided into two subspecies: fastening on the shoulder and on the wrist. All of them differ in the type and order of measurement, they also have pros and cons. But automatic models are considered the most accurate and reliable. For home use, you can purchase any of them, it is important to consider the functionality of the device, its cost and reliability.

The device of a mechanical tonometer and the principle of operation

Mechanical devices are divided into mercury manometers and membrane.

How does a mercury manometer work?

mercury manometer

The very first device for measuring indicators was a mercury mechanical one. At present, it is practically not used. But it is considered the most accurate device for measuring blood pressure. It differs from modern ones in the presence of a mercury scale. Her column rises to the desired number - this is blood pressure. The rest of the devices do not differ from modern ones: a cuff attached to the shoulder, a pump for supplying air, a phonendoscope for capturing tones. The device is unsafe - if you move it carelessly, the scale with mercury can fall out and break, and the toxic liquid can spread across the floor. Therefore, this device was discontinued.

How does a mechanical membrane tonometer work?

Its work is due to the presence of a sensitive part - the membrane. This is a flexible plate that bends under pressure and, under the action of additional mechanisms, moves the arrow on the pressure gauge scale. The device quite accurately displays the indicator of the state of health, is safe and has a wide range of applications. It is considered a professional tonometer, it is equipped with all medical institutions. For correct use skills are needed, medical personnel are trained in them. At home, it is difficult to measure pressure on your own, the main difficulty lies in listening to tones.

Mechanical tonometer

The measurement order is as follows:

1. Place the cuff on your forearm, slightly above the elbow.
2. Place the phonendoscope on the vessel in the fold area.
3. Fill the cuff with air using a bulb.
4. Gradually releasing air from the cuff with a special valve, listen to the tones and look at the arrow.
5. The first "knocks" are systolic pressure.
6. The final one is the diastolic indicator.

Modern manufacturers simplify the device device. There are models with an inserted phonendoscope in the cuff. And for some, the pear is combined with the scale.

The advantages are listed by the following factors:

• low cost;
• high measurement accuracy;
• simple device and durability of application.

The disadvantages of the device include:

• measurement requires special skills, keen hearing and good eyesight;
• it is difficult to measure without outside help, otherwise the indicators will be distorted;
• No additional features.

For home use, it is better to purchase a different type of tonometer.

About electronic devices

Electronic devices are divided into semi-automatic and automatic. Similar principle work, but there is a difference in use.

How does a semi-automatic blood pressure monitor work?

Semi-automatic tonometer

This type of device also has a pear and cuffs, but instead of a scale - an electronic screen and buttons for control. It is quite similar to the mechanical apparatus, but is simpler to operate. With a pear, you need to fill the cuff with air, and then wait until the tonometer itself processes the signals and displays the indicators in large numbers on the display.

The tonometer works from electrical network or battery operated. The device is compact, quite accurate in readings and equipped with additional functions.

The advantages of the device are the following features:

• good accuracy, error up to 3 mm Hg. st;
• average cost;
• no need to listen to the "knocks" and follow the pressure gauge needle;
• compact, it is convenient to carry it with you;
• it has few electronics and reduces the risk of breakdowns;
• equipped with functions such as determining the heart rate, is able to remember the time of the previous measurement.

The device has negative sides:

• air supply with a pear increases the risk of distortion in measurements, it is especially difficult for the elderly;
• there is a need to replace the batteries, their discharge usually happens at the wrong time;
• there are also breakdowns that require repair in the workshop.

But it is still the most popular tonometer used in everyday life.

Electronic blood pressure monitor: what are its principles of operation?

This is the most expensive device of all types of tonometers. The kit includes a cuff and a electronic device. As soon as the cuff is put on the forearm and the button is pressed, the electric pump built into the device pumps air into it. The entire measurement process takes place automatically, the sensors process the indicators and display them in a digital image on the display screen. Tonometers are quite fragile and require careful handling. Easy to use and small in size. No need to ask for help from outside, but just sit comfortably and relax. It can work from mains or batteries.

Automatic blood pressure monitor

Advantages of an electronic tonometer:

• they can measure blood pressure correctly, reducing the risk of incorrect readings;
• measurement error - 3-5 mm Hg. st;
• the procedure is quite simple and accessible to older people;
• small device.

But the latest model of tonometers also has disadvantages:

• high price;
• the presence of an error;
• short service life.

The new models of automatic blood pressure monitors have many different functions that allow you to track not only pressure. It is necessary to list only the most popular and common:

• the device reminds you of the time of the previous use;
• the presence of an arrhythmia indicator;
• the presence of an indicator of the correct fixing of the cuff;
• shows the average result of several measurements;
• automatically turns off after work is completed.

There are other functions such as calendar, clock, cuff inflation indicators and many others.

Wrist-mounted electronic blood pressure monitor

Among the electronic blood pressure monitors there is a model that measures the pressure on the wrist. This device does not have a cuff, but is simply fixed in the area of ​​\u200b\u200bthe wrist, indicators are displayed on the screen. In order for them to be accurate, having fixed the device in place, you need to sit down and relax, hold your hand with the tonometer at chest level.

Device on the wrist

This model reduces pressure measurement time and is ideal for athletes because they can monitor the readings during training. True, there is a drawback - this is a high error during the exercise. Physicians recommend using this model people under 40 years old. In the older generation, the vessels wear out, especially in the wrist area, which reduces the reliability of measurements.

Advantages of a carpal tonometer:

• light weight and dimensions, it can be carried with you everywhere and always;
• ease of use, you do not even need to undress;
• the ability to take measurements anywhere and even on the run;
• no need to pick up the cuff;
• has many functions available to a conventional automatic tonometer.

Cons of a carpal tonometer:

• there are restrictions on the use of age;
• very fragile device, requires careful use;
• when moving, it shows results with a large error;
• high price.

Buying this species device, it is necessary to take into account the listed disadvantages and limitations.

How to choose the best

Knowing what blood pressure monitors are, all their advantages and disadvantages, you can quite easily pick up a device to use at home. Before making a purchase, you need to know some nuances:

• What diseases does the patient have? The frequency of use of the device and its adaptation to the disease depend on this.
• Can the patient learn to use different types of devices.
• Price policy.

It is important to first decide which device you need: according to the principle of operation or at the place of installation. Buy at a pharmacy or a special medical equipment store. First you need to check if there are instructions on mother tongue, warranty card, verification mark.

You also need to inspect the device for build quality, how all the details fit, ease of opening and closing the battery compartment. Check all additional functions, ask the sales assistant to make settings.

The mechanical tonometer guarantees the accuracy of pressure measurement and has no high cost, but a person with good hearing and able to learn how to handle the device should work with it. For older people who control their condition themselves, only an automatic blood pressure monitor is suitable. He does everything himself, you don’t even need to expend energy on inflating the cuff. If the patient had a stroke or a heart attack, there is an arrhythmia, he must have a function of intellectual sensitivity.

Most bought brands

The most sought-after brands of blood pressure monitors are manufactured by Omron, a diversified corporation in Japan, by AND and a Japanese brand operating in the field of high technology Citizen. Also, tonometers of the Swiss corporation Microlife and the American company Meditech are in great demand. Firms are also in demand: Japanese - Nissei and English - B. Well.

List of popular brands

Among the most popular mechanical models are:

• WM-61, B. Well - good accuracy and quality of the manometer. The price is low - 780 rubles.

Mechanical tonometer model WM-61, B. Well

• Microlife BP AG 1-40 - large pressure gauge and cuff size. It has high accuracy. The cost is affordable - 1890 rubles.

Tonometer model Microlife BP AG 1-40

• Ri-Can 141 is an improved model for individual use. Provides maximum accuracy. The price is high - 5950 rubles.

Among the semi-automatic:

• Microlife BP N1Basic - improved quality and accuracy of test results. The price is low - 1450 rubles.
• The Omron S1 is a reliable instrument with many features. average price- 1640 rubles.

Semi-automatic model Omron S1

• B. Well WA-22H - excellent accuracy and build quality, improved design, additional convenience in design. Low price - 1690 rubles.

Blood pressure monitor model B. Well WA-22H

The best automatic models:

• Microlife BP A2 Basic is a high-quality universal device for the whole family. The average price is about 3 thousand rubles. Has numerous features.
• Omron M2 Basic with adapter - reliable readings and comfortable operation. They can measure indicators once, and this will be the correct result. average cost- 2450 rubles.

Omron M2 Basic with adapter

Cardiologists advise that for those over 40, it would be better to purchase either an automatic machine with a cuff attached to the shoulder. Young people can also measure pressure with a carpal apparatus.

It is necessary to acquire a suitable tonometer for individual use, taking into account all the characteristics of a person, his illnesses, age, and the need for various functions. The device is especially required for patients with hypertension and stroke survivors in order to control pressure and prevent complications.

A tonometer is a device designed to measure blood pressure (BP). With its help, it is possible to ensure the prevention of pathologies of the cardiovascular system - especially arterial hypertension. Today there are many varieties of such devices. To choose suitable option, a number of criteria must be taken into account.

Normal blood pressure in a healthy person is 120/80 mm Hg. Art. Some people are characterized by lower or higher parameters, which is also a variant of the norm. However, a strong deviation from these values ​​indicates the development of dangerous diseases. To identify these violations, it is worth using a special device - a tonometer.

This device must be in home first aid kit in people who suffer from hypertension. To prevent the development of a hypertensive crisis, such people should constantly monitor their pressure. According to its results, the doctor selects an adequate treatment.

The need to use a tonometer is not always associated with hypertension. After 50 years, pressure often increases due to a violation of the general state of health. In such a situation, it is also necessary to measure the pressure in order to help the person in time.

Athletes often need a device to control the level of physical activity (modern devices allow you to measure not only blood pressure, but also pulse). In addition, the need for a tonometer is experienced by people who often face stressful situations or constant psycho-emotional stress.

People who have diabetes and hypotension should control the pressure parameters. It is also required to monitor such indicators during the period of bearing a child.

Important: If a person often has headaches, nausea, dizziness, pain in the heart, this indicates a deviation in blood pressure from the norm, which is fraught with dangerous consequences.

The use of a tonometer allows you to identify violations in the body. A timely call for an ambulance can save a person's life.

Types of tonometers

The classification of such devices is based on the principle of operation. There are mechanical, automatic and semi-automatic devices. They are also classified according to the area of ​​​​measurement. According to this criterion, carpal and shoulder devices are distinguished. The latter are used more often due to the high measurement accuracy.

Note: There are also devices for monitoring blood pressure on the finger, but their accuracy is not so high.

Mechanical tonometer

Many people are interested in what this type of tonometer consists of. The device includes such elements as a cuff, a phonendoscope, a pear and a pressure gauge. The last element is mercury or membrane. Mercury is considered more accurate.

In some models, the phonendoscope is connected to the cuff. A mechanical tonometer has the most affordable cost, but its use requires certain skills and good hearing. Sometimes people cannot measure correctly with such a device. The accuracy of the obtained values ​​directly depends on the skills of the person.

The mechanism of operation of the device is based on the oscillometric technique. In this case, there is an electronic processing of the vibration that is generated in the cuff. This makes it possible to eliminate the human factor and reduce the risk of errors.

A semi-automatic pressure measuring device involves manual air injection. After that, the electronic device records the parameters of blood pressure and heart rate (HR). According to the principle of operation, the semi-automatic device coincides with the automatic device.

Automatic blood pressure monitor

These devices are considered the most convenient. They make it possible to measure pressure without applying special efforts. This is due to the fact that the management of a modern automatic tonometer is simple.

To take measurements, put on the cuff, take a comfortable position and press the button. After a while, the results will appear on the monitor. The machine has a fairly low error. But if a person has an arrhythmia, the pressure will have to be measured several times.

The automatic tonometer works from accumulators or batteries. Some models include a network adapter. It allows you to use the device by connecting to the network.

Such devices are required for people who need constant monitoring of pressure. It is convenient to use them, since it is difficult to measure every half an hour with a traditional device. The procedure is called "24-hour blood pressure monitoring."

The tonometer for daily monitoring is designed so that the cuff is put on the arm, and the device itself is attached to the belt. Such products have compact dimensions. During the day they take measurements every 15 minutes, at night - every 30 minutes.

These devices allow you to determine the conditions under which pressure rises during the day. This makes it possible to take preventive measures in time.

The device and principle of operation of the tonometer

There are two main methods for measuring pressure - auscultatory and oscillometric. The first method was invented at the beginning of the last century by the Russian doctor N. S. Korotkov. Since then, he has not undergone major changes. The basis of this technique is listening to the sounds that appear in the body when the artery is squeezed.

Tonometer device mechanical type includes the following elements:

• cuff - it is put on the part of the arm that is located between the elbow and shoulder;
• pump - used to pump air into the cuff;
• mercury or membrane tonometer - it shows the air pressure that appears in the cuff;
• A phonendoscope is also called a stethoscope and is used to listen to noises.

The principle of operation of the tonometer is as follows:

In the case of using the oscillometric technique, fluctuations in air pressure in the cuff are recorded. Its appearance is influenced by the blood flow in the compressed part of the artery. In such a situation, there is no need to use a phonendoscope. Through electronic device pressure fluctuations are transformed into electrical signals.

Then the automation analyzes them. As a result of this process, numerical indicators appear on the screen. Depending on the functions of the device, it will be possible to obtain not only pressure parameters, but also the heart rate, as well as information on the development of arrhythmia.

Many devices can store this data in their memory. This allows them to be analyzed and monitored for a long time. Based on these data, the doctor can choose the appropriate treatment.

Cuff Features

One of important elements tonometer is a cuff. It is a fabric shell, inside of which there is a rubber chamber. On top of the cuff there are fixing Velcro. Wear this element on the shoulder or wrist.

The cuff has different sizes - it all depends on the person's hand. For measurements to be as accurate as possible, it is important to choose the right right size. In this case, the length of the pneumatic chamber should be as close as possible to the girth of the patient's arm.

The size is determined by 2 numbers:

• for children, coverage is 15-22 cm (small, S);
• medium cuffs are 22-32 cm (medium, M);
• large - 32-42 cm (large, L).

Important: The cuff should be chosen one that best matches the indicated values ​​\u200b\u200band the circumference of the arm. To determine the girth of the shoulder, you need to focus on middle zone between the fossa of the elbow and the level of the clavicle.

Wrist devices are usually different small size cuffs, therefore they are not always suitable for overweight people.

Additional functions

To facilitate the use of the tonometer, modern devices have additional features. Their number depends on the model of the device. The choice of a particular device is determined by personal wishes and financial capabilities.

So, these functions of tonometers include the following:

A carry bag is often included as well. It allows you to store the device and facilitates its transportation.

Selection rules

Before buying a tonometer, you need to pay attention to the following indicators:

• measurement error, stability of the obtained results;
• ease of use;
• mains or battery powered, adapter available;
• cuff size;
• troubleshooting guarantee.

In addition, there are the following criteria that you should definitely consider:

Many people make a choice between mechanical and automatic devices. Each of specified categories device has certain advantages and disadvantages. To key benefits mechanical devices include the following:

1. High accuracy. Such devices provide reliable results. Mechanical devices are often used in medical facilities.
2. Ease of maintenance. The device does not require battery charging or battery replacement. Sometimes there are problems with a pear, but this part of the tonometer can be easily replaced.
3. Widespread. These traditional models are known to almost everyone.
4. Affordable cost. Mechanical blood pressure monitors are considered the most inexpensive.

The disadvantages of such devices include difficulties in self-conduct measurements. It can be difficult for elderly patients to understand how the device works. In addition, the readings of the moving arrow cannot be fixed by people with poor eyesight.

It also takes effort to measure. During the procedure, you need to compress the pear to pump air into the cuff.

Automatic devices also have a number of advantages. These include the following:

The disadvantages of such pressure meters include higher cost and the need for power supply. This also creates some difficulties when using the tonometer by elderly patients.

Popular manufacturers

Today there are many companies that produce such devices. The most popular brands include the following:

• Microlife (Microlife);
• Omron (Omron);
• Nissei;
• beurer.

Each of these brands has its own advantages. When choosing, people are guided by their financial capabilities and the required functions of the device. When in doubt, it is best to consult a doctor.

A tonometer is a device that allows you to monitor blood pressure. Today, there are many devices that differ in the principle of operation and the presence of additional functions. Thanks to this, each person can choose the appropriate device depending on their needs.

Heart disease is one of the three most common ailments in the world. Abnormal blood pressure is a sure sign of the development of problems with the main vital organ.

A first-class tool for detecting and preventing heart disease is a tonometer. Each medical device has its own "biography" and features. Next, we will consider device and principle of operation of the tonometer, as well as their types and features of choice.

Tonometer: a look into history and relevance

The first prototype appeared in France in 1828. The doctor Jean Louis Poiseuille used a special manometer to measure the pressure.

The device worked on the basis of mercury. By means of a cannula, it was introduced into the artery, which made it possible to determine blood pressure in real conditions.

A non-invasive (without direct penetration into the tissue) method was released only after almost 30 years. The German physician Karl von Fierordt invented a special device, later called the sphygmograph, in 1854. The technology has rapidly gained popularity and credibility in the medical community.

Initially, blood pressure was measured in animals. The man was remembered only in 1856, when the famous surgeon Favre connected the device to the human artery during the operation.

The world-famous classic tonometer appeared in 1905 after the report of Nikolai Korotkov, the great Russian surgeon.

In 1965, doctor Seymour London improved Korotkov's invention and released automatic variety, which entered medical use in parallel with the traditional model.

At present, the demand for the device is difficult to overestimate. Statistics eloquently testify: more than half of the world's population has high blood pressure. Cardiovascular have become a real scourge of our time. They are “getting younger”: more and more often young people suffer from heart ailments. The CIS countries have not bypassed the attack either. Hence the need for timely detection of diseases. The device is traditionally included in the arsenal of essentials for the elderly and people suffering from heart disease.

The device and principle of operation of the tonometer

All meters can be divided into two large classes:

• Mechanical. traditional models. They consist of a cuff (special strap), an air blower (the so-called pear), a stethoscope and a pressure gauge.
• Automatic. Produced on the basis modern technologies. Consist of electronic stuffing and cuff.

There are so-called semi-automatic tonometers. They do not have independent significance, since they are a kind of combination of existing classes.

Mechanical varieties are still in use today.

Huge popularity arose due to the simple and unpretentious design of the device. Features of the device of mechanical tonometers:

• Large range of cuffs. There are "sleeves" for both the elderly and children.
• The supercharger (pear) has two valves: check and discharge. The former holds the air in the cuff, the latter releases it.
• The stethoscope is a rubber tube used to listen to heart sounds.
• The pressure gauge displays the data on the display. The moving arrow indicates the existing blood pressure.

The principle of operation of a mechanical tonometer: the "sleeve" compresses the air, which is gradually pumped by the pear. At this time, with the help of a stethoscope, heart rhythms are heard. The result will be displayed on the device screen.

The traditional measurement site is the shoulder. No one forbids determining pressure in other places, but it is precisely on the shoulder that accurate and stable data are recorded.

An automatic blood pressure monitor is a more technologically advanced option for measuring blood pressure. Device Features:

• Lack of an air blower (pears). There is only a cuff and an electronic unit.
• The equipment can store information about previous measurements.
• One button on the pressure gauge starts the whole process.
• Availability of additional features. Automatic meters can measure the body position indicator, arrhythmia and other indicators.

The pressure is measured using the oscillometric method. Principle of operation: the air in the cuff is gradually pumped up and discharged by a special compressor.

The device monitors air fluctuations in the cuff, which occur due to the flow of blood in the clamped area. The fluctuations are converted into signals which are translated into digital values ​​on the display.

Choice of tonometer - mechanical or automatic

Advantages of mechanical meters:

• Accuracy. Devices with a high degree of reliability determine blood pressure. "Mechanics" can often be found in medical institutions.
• Unpretentiousness. No need to recharge or change batteries. There may be problems with the pear, but the element can be easily replaced with another one.
• habit. Classic models known to almost everyone.
• Cheapness. The purchase does not require large investments.

Among the shortcomings, one can single out the complexity of measurement. It is sometimes difficult for older people to understand the principle of operation of the device, and the indications of a moving arrow are often simply unreadable for people with poor eyesight. It also requires some effort to measure: the pear must be compressed to inflate the cuff.

Advantages of automatic models:

• The convenience of use. All that is required of a person is to put on a cuff and press a button. The instrument will take the measurement on its own.
• Intuitive interface. Producers work to please consumers.
• Diversity. The market is replete with dozens of models with any configuration.
• Digital display. Indicators are displayed clearly and clearly. There are no arrows. Automatic apparatus Ideal for people with poor eyesight.

Among the disadvantages: the need for recharging and high cost. The electronic unit will have to be recharged over time. With high price An interesting paradox is connected: immodest price tags should repel the target audience represented by older people.

In fact, there is an opposite pattern: automatic models are just acquired because of the simplicity and clarity of use. Mechanical varieties are used mainly by doctors.

There is no better option. A person prefers what is familiar. There is a wide range of medical devices on the market with different settings and functions. You can easily find the right device.

A tonometer is a device that has been in the service of mankind for several hundred years. Times change, but heart disease remains the same. Identification and prevention of possible diseases associated with the heart and - the primary task of such effective instrument like a tonometer.

Blood pressure (BP) problems can be experienced by people themselves different ages. Such a pathology of the cardiovascular system as arterial hypertension is observed in about a third of the adult population. A disappointing figure, plus the older a person becomes, the higher the risk of being affected by this disease. It cannot be ignored - the consequences can be too serious. Among them are strokes and heart attacks, dizziness, just feeling unwell. Very often, the quality of life, and life itself, depends on how much the pressure has risen or dropped.

In order to keep blood pressure under control and always be aware of its changes, special devices are used - tonometers. They were invented back in 1876, but have reached our time in a completely different form. Initially, it was a large rubber balloon filled with water. It, connected to a manometer with a tube, was placed above the artery. Approximately two decades later, a more familiar version appeared with a cuff that is applied to the shoulder, and to determine the pressure, pulse was used while taking into account the values ​​​​of the mercury manometer. Naturally, to obtain more or less accurate results, some experience and skill were required.

Classification of modern tonometers

Modern tonometers can be classified in two ways. different ways. First: according to the method of measuring blood pressure. Second: according to the method of fastening (the place where the cuff is applied).

Blood pressure measurement is carried out using the following models:

• mechanical: when the value of the parameter is shown by the arrow on the dial;
• digital (automatic and semi-automatic): when the value is displayed digitally on the screen;
• mercury: when the pressure value is determined by the level of the mercury column.

There are also three ways to apply the cuff:

• on the finger;
• on the wrist;
• on the forearm.

The first criterion that guides when choosing a tonometer is the method of measurement. We will dwell on it in detail, and list the rest in an overview.

Mercury blood pressure monitors

Mercury models are among the very first to appear on the market, but they differ markedly from their prototype, developed by the doctor Riva-Rocci, both in terms of workmanship and precision. Structurally, such a device consists of a mercury manometer with graduations printed on it, a pear and a cuff. Using a pear, air is pumped into the cuff, while listening to tones with a stethoscope or phonendoscope. The pressure level is determined by the level of the rise of the mercury column. Most often, mercury models are professional, they can be found in medical institutions.

The advantage of such a device is a very good accuracy in determining blood pressure, and the disadvantage is the pronounced toxicological properties of mercury, which greatly limits its scope.

Mechanical blood pressure monitors

Mechanical blood pressure monitors are well-deservedly popular among medical personnel even in modern medical institutions; they are most often purchased by the elderly. Structurally, such tonometers consist of a cuff, a rubber tube through which a rubber bulb is connected, a phonendoscope and a pressure gauge with an arrow and a scale. The principle of operation of a mechanical tonometer is as follows: the cuff is applied to the shoulder, air is pumped with a pear, and at this time, heart rhythm tones are heard using a phonendoscope. The measurement results can be observed on the screen of the pressure gauge, they will be indicated by a moving arrow.

The advantages of such a device are accessibility (in terms of cost, this is the most cheap option), high accuracy of blood pressure determination, the least influence on the readings external factors(hand movement, talking during measurements, etc.), no need for special care behind the device.

The disadvantage of a mechanical tonometer is that often the accuracy of the measurement directly depends on the skills of the one who makes these measurements, as well as his accuracy of hearing and vision. The more experienced a person measures pressure, the more likely it is that the results will be as close to real as possible.

Semi-automatic blood pressure monitors

Unlike the two previous varieties, semi-automatic tonometers are always equipped with an electronic display that displays the measurement results. At the same time, data are displayed not only on the level of blood pressure, but also on the frequency of heart contractions (pulse). The display in this case replaces the pressure gauge, otherwise everything is the same as in a mechanical tonometer: a pear, with which air is pumped, a tube and a cuff. Of the additional features in such tonometers, there may be a backlight, sound alert about the completion of measurements, memory for several previous measurements of blood pressure.

The advantages of semi-automatic models are that they are still available against the background of fully automatic ones, but at the same time they provide more possibilities to measure than mechanical. It turns out that they are a kind of compromise between price and feature set. The presence of the display will definitely be appreciated by the elderly and those who suffer from hearing and / or visual impairments. And this device is completely universal and autonomous due to the lack of requirements for recharging and the use of additional power sources (batteries).

Among the shortcomings, it is worth highlighting the fact that they still need to apply a certain physical effort to force air into the pear (and not every elderly person can handle this), and the result may be inaccurate if you do not follow the instructions for using the device. Due to errors, it is recommended to perform two or three blood pressure measurements in a row, and then calculate the arithmetic mean - this value will be as close as possible to the real one.

Automatic blood pressure monitors

Automatic blood pressure monitors are the most advanced in technical terms, but also the most expensive. They no longer need to pump air with a pear, and the pear itself is missing. There is only a cuff and a block with a digital display connected to it by means of a tube, air is pumped automatically and without mechanical effort on the part of a person. These measuring instruments can be designed to be worn on the shoulder, wrist and finger. To turn them on, just press the button on the manometer case, and after a few seconds, information about the value of blood pressure, heart rate and other indicators will appear on the screen, depending on the selected model. Additional features they are the same as in semi-automatic models. In addition, they can have a motion indicator, an indicator of the correct position of the human body during measurements, an arrhythmia indicator, and other functions.

The advantage of automatic blood pressure monitors lies in their ease of use, the absence of skills requirements for working with it, the ability to measure pressure in any conditions (in medical institution, at home, or even right on the street in emergency situations). Some models use two methods at once to improve the accuracy of measurements: the classical oscillometric method and the Korotkov method.

However, they also have enough shortcomings: for example, this is a low accuracy, which can be improved only by conducting a series of successive measurements. The high cost of such blood pressure monitors often scares off ordinary pensioners - the main target audience of these devices. Plus, due to medical reasons, they are not recommended for people with arterial hyperextension.

How to choose a tonometer

As already mentioned above, the first selection criterion will be the type of tonometer, which is determined by the method of measuring blood pressure. The remaining parameters are less critical, but you still need to take them into account in order to eventually get a really convenient and functional device.

If the tonometer is bought for individual use, you need to take into account all the features of the body of this person. First, his age. Young and middle-aged people leading enough active image life, we can recommend wrist-mounted blood pressure monitors, for the elderly - automatic and semi-automatic models. However, in the latter case, the material factor can play a significant role, in which case the choice can be stopped on a mechanical device.

The presence of certain diseases of the cardiovascular system can also be an important factor that cannot be ignored. In the case of arrhythmia and tachycardia, automatic and semi-automatic models are suitable, which can sequentially take up to three measurements in a row and then compare them on the screen. With vascular atherosclerosis, only semi-automatic and automatic tonometers are suitable, since listening to heart sounds with a phonendoscope is difficult in such cases.

All models with cuffs must be selected according to the size of the arm of the person or group of people who will use the device. The vast majority of devices have a standard cuff diameter, but on sale you can also find those that are focused on the use of very obese people. The diameter of the circle in them can reach 42 cm. Do not forget that from correct fastening cuff often depends on the measurement accuracy!

Pay attention to the material of manufacture of the phonendoscope - it is better if it is metal, not plastic. And the point here is not at all in the durability of the first, but in the fact that the polymer structure worsens the sound, and, accordingly, makes it difficult to work with the device. The pressure gauge case is also better to choose metal.

If both adults and children have to measure blood pressure with a tonometer, you can immediately buy a model in which you can change the cuffs. It will be much more comfortable to put a child's cuff on the child's hand. This feature is usually provided in automatic and semi-automatic models.

The presence of backlight is not critical, but very useful property, especially if the tonometer is planned to be used at night. With it, the numbers on the screen will be much easier to parse.

Popular manufacturers and models of pressure gauges will be discussed in the next article.

Content

Introduction 4

1 Purpose and scope 5

2 Product Specifications 6

3 Review of existing solutions and rationale for the choice of structure 7

3.1 Overview of existing solutions 7

3.1.1 Omron automatic blood pressure monitor, M10 IT 10

3.1.2 Semi-automatic tonometer M1 Plus 11

3.1.3 Mechanical tonometer LD-81 12

3.2 Rationale for the choice of control structure 13

3.3 Description of the principle of operation of the tonometer according to the functional diagram 14

^ 3.4 Model development 17

4 Structural scheme and description of individual components 24

4.1 Structural diagram 24

4.2 IR emitter AL107A 32

4.3 Photocell FD256 33

4.4 Op-amp of the KR (KF) 1446UDxx 35 series

^ 4.5 Liquid crystal module MT–10S1 40

4.6 Microcontroller ATmega128 42

4.7 Level converter DS275 48

4.8 Stabilizers LM78L05 and LM78L12 50

4.9 Filter calculation 52

5 Development of the scheme of the algorithm and the control program 56

^ 5.1 Main function algorithm 56

5.2 Algorithm of initialization function 57

5.3 Algorithm of the pulse wave reading function 58

5.4 Algorithm of the mean pressure calculation function 59

^ 5.5 Algorithm of the systolic pressure calculation function 60

5.6 Algorithm of the display function 61

6 Circuit diagram description 62

^ 6.1 Description individual elements 62

6.1.1 Analog circuits 62

6.1.2 Microcontroller 63

6.1.3 Communication devices 63

6.1.4 Power circuit 63

Conclusion 64

Annex A 65

Annex B 67

Introduction

Today at modern medicine and everyday life is acutely facing the issue of new diagnostic tools. An accurate diagnosis is impossible without continuous monitoring of a person's vital signs, such as blood pressure, pulse rate, body temperature, etc. Unfortunately, on this moment not all of these parameters can be accurately measured in real time - existing instruments are either not accurate enough, or the measurement methods are invasive, i.e., they can affect the measurement result.

The device can be made on an inexpensive existing element base, does not require highly qualified personnel, and is suitable for use outside medical institutions.

^

1 Purpose and scope

The designed device is designed to answer the acute question about new diagnostic tools. Accurate diagnosis is impossible without continuous monitoring of human vital signs, such as blood pressure, pulse rate, body temperature, etc. Unfortunately, at the moment, not all of these parameters can be accurately measured in real time - existing devices are either not accurate enough, or measurement methods invasive, i.e. they can influence the measurement result.

This paper presents a project of a device for non-invasive measurement of blood pressure and heart rate (pulse). Such a device allows you to take readings quite often, and in combination with a computer and data storage means, to keep detailed statistics on changes in these readings and thus even predict a possible further deterioration in well-being.

^

2 Device Specifications

In progress term paper a device was designed for non-invasive measurement of mean, systolic and diastolic blood pressure, as well as heart rate (pulse).

The device has the following characteristics:

• 
  relatively low cost of production, achieved by the use of widely used components;
• 
  high measurement accuracy;
• 
  no influence of the fact of measurement on the result;
• 
  versatility of application;
• 
  flexibility achieved by using standard components and using portable code;
• 
  genious idea;
• 
  ease of scalability, connectivity additional sensors or other automation devices;
• 
  compatibility with standard interfaces;
• 
  ease of operation;
• 
  ease of modification and adaptation of the code;
• 
  wide operating temperature range.

^

3 Review of existing solutions and rationale for the choice of structure

3.1 Overview of existing solutions

To date, there are several various devices to measure blood pressure, but, unfortunately, they work on the principle of forcing air into the cuff, i.e. are invasive means of measurement and cannot be used for permanent monitoring. There are also devices for non-invasive readings, but they are too expensive or not accurate.

A method for continuous monitoring of systolic blood pressure and an apparatus for its implementation are known (US patent N 4030485 dated 06/21/77, MKI A 61 B 5/02), which consists in the fact that using a calibration device with a light converter that converts changes in light intensity into changes in the amplitude of the electrical signal, measurements of the light intensity are determined, corresponding to a change in the volume of blood in the tissue under the transducer, the amplitude of the differential signal is periodically sampled and the amplitude of the signal corresponding to the reference pressure is summed with it. The amplitude of this signal is proportional to the systolic pressure.

disadvantage this method is low information content due to the fact that only systolic pressure is determined.

A known method for measuring mean pressure along a curve obtained from the results of measuring blood pressure (Germany, application N 0S 3511803 dated 9.10.86, MKI A 61 B 5/02), which consists in the fact that the received signal of the blood pressure curve is converted into digital form and on the segment of the blood pressure curve, which is less than the respiratory cycle, Min is determined, and in the Min zone there is section F extending on both sides for at least one cardiac cycle, inside the section F, the largest amplitude value Max and two threshold values ​​S1 and S2 are determined, corresponding 1/3 and 2/3 nai greater value amplitudes A1, A3, which is greater than the larger value of S1. Based on this amplitude value A1, A3, the next amplitude value A2, A4 is found which is smaller than the threshold value S2. This allows you to determine between successive amplitudes A1, A2 - A3, A4 Max 1, Max 2. The measured values ​​between these maxima Max 1 and Max 2 determine the average pressure.

The disadvantage of this method is the low information content due to the fact that only the mean blood pressure is determined.

A known method and device for indirect measurement of blood pressure (EPO, application 0136212 dated 03.08.83, MKI A 61 B 5/02), consisting in the fact that at least one sensor is used, held with a focus in the hole, where the pulse is determined, with a constant effort, which is less than the effort created by the diastolic pressure of the blood flow in the radial artery. The maximum and minimum values ​​of the pressure signals are determined, the average value of the ratios of the maximum and minimum values, calculate systolic and diastolic pressure and show them on the indicator.

Closest to the proposed product is a method and apparatus for automatically determining the systolic, diastolic and mean blood pressure of a patient (France, application N 2593380 dated 27.01.86, MKI A 61 B 5/02), designed to determine blood pressure in a non-invasive way. The apparatus has a two-channel amplification line containing an amplifier and a filter in series. Both analog signals from the two channels are digitized by an A/D converter. The monitor has, in addition to the converter, a microprocessor with a program block.

The disadvantages of this method and device are limited scope, low quality registration through the use of piezoelectric sensors.
^

3.1.1 Omron automatic blood pressure monitor, M10 IT

The main difference between an automatic tonometer and a mechanical one is its ease of use. To measure pressure with an automatic blood pressure monitor, you just need to fix the cuff on your arm and press the button. After a few seconds, the measurement result will appear on the screen of the device.

Figure 3.1.1.1 Omron M10 IT automatic blood pressure monitor

Specifications:

• 
  Measurement method: oscillometric;
• 
  Accuracy class: clinically tested;
• 
  Arrhythmia indicator;
• 
  Sound signal;
• 
  
• 
  Cuff size, see: 22-42;
• 
  Averaging results;
• 
  Measurement accuracy: pressure within +/- 3 mm. Hg;
• 
  Measurement accuracy: pulse within +/- 5% of readings.

^

3.1.2 Semi-automatic tonometer M1 Plus

Semi-automatic blood pressure monitors differ from automatic models in that in order to measure pressure, it is necessary to independently pump air into the cuff of the device using a pear. At this time, the semi-automatic tonometer directly measures blood pressure on its own.

The accuracy of blood pressure readings when measured with a semi-automatic sphygmomanometer is the same as when used.

Figure 3.1.2.1 Semi-automatic tonometer M1 Plus

Specifications:

• 
  Accuracy class: A/A;
• 
  Arrhythmia indicator: yes;
• 
  Sound signal: yes;
• 
  Memory capacity: 21 measurements;
• 
  Batteries: 4 AA batteries;
• 
  Cuff size, see: 22-32.

^

3.1.3 Mechanical tonometer LD-81

Figure 3.1.3.1 Mechanical tonometer LD-81

Specifications:

Pressure measurement range from 20 to 300 mm Hg.

Limits of permissible absolute error of the device when measuring pressure in the cuff at a temperature: from 18 ° to 33 ° С to +/- 3 in the range from 60 to 240 mm Hg. (up to +/- 4 in other ranges). from 5° to 17° C and from 34° to 40° C to +/- 6.

Instrument operating conditions: ambient temperature from + 10° C to + 40° C, relative humidity from 30% to 85%, atmospheric pressure from 86 to 106 kPa, storage and transportation temperature from - 34° C to + 65° C.

Standard adult cuff size (arm circumference approximately 25 to 36 cm).

The mass of the device is not more than 340 g.
^

3.2 Rationale for the choice of control structure

The task of this product is to develop a method for determining blood pressure based on the assessment of shifts in the corresponding points of pulse waves using the proposed device, which would simplify the measurement procedure, improve the quality of pulse wave registration, and expand functionality.

The principle of operation is that a pulse wave is recorded on the radial artery by two optoelectronic sensors, the coordinates of the maximum amplitudes of the pulse waves are measured, the modulus of the difference in the values ​​of these coordinates is measured, by the value of which the mean arterial pressure is determined, the diastolic blood pressure is calculated from the value of half the difference of the tripled value of the mean and systolic pressure, the first derivatives of these pulse waves are recorded, the offset between the maximum amplitudes of the first derivatives of the pulse waves at their inflection points is measured, the value of which is used when determining the systolic blood pressure by means of a correction factor.

A detailed diagram of the designed device is described below.

^

3.3 Description of the principle of operation of the tonometer according to the functional diagram

Figure 3.3.1 Functional diagram

^

3.4 Model development

The device for non-invasive blood pressure measurement contains two sensors made on optoelectronic elements, two channels of low-pass filters and two channels of amplifiers, the inputs of which are connected respectively to the outputs of the first and second optoelectronic sensors, two differentiators, an analog-to-digital converter, a microcontroller, a display and a communication port.

Description of the functional diagram of the operation of the device shown above: a silicone product is fixed on the patient's radial artery, equipped with two infrared emitters and two photocells.

The light from the emitters is completely internally refracted, so the voltage at the output of the photocells is zero.

When a pulse wave passes through the artery, the silicone product is deformed, thus, a light flux begins to flow to the photocell, which leads to the appearance of a non-zero voltage at the output of the photocell.

Two identical transmitter-receiver pairs are placed along the artery, i.e. the pulse wave observed under each of the sensors is the same wave shifted in phase.

Due to the semiconductor nature of the photocell, as well as for other reasons, high frequency noise will be present at the output of the photocell. To filter noise in each channel, a low-pass filter is provided, the calculation of which is given below.

After filtering, the signal must be amplified to a level of about 5V. For these purposes, an amplifier on an operational amplifier chip is used.

The resulting amplified and noise-free signal is fed to the differentiator, after which 4 signals (2 amplified and they are the same, but differentiated) are fed to a 10-bit ADC, after which they are processed in the microcontroller. According to the established algorithms and formulas, MK calculates the mean, diastolic and systolic blood pressure and pulse rate.

After receiving the result, it is displayed on the LCD and transferred to the PC for analysis and storage via the communication port (RS-232)

Figure 3.4.1 Two optoelectronic sensors

Paired optoelectronic sensors 1 and 2 are located on the radial artery. The radiation generated by the radiation source, reflected from the studied area of ​​the vessel, is modulated in amplitude by blood flow pulsations. The modulated flow is converted in the photodetector into an electrical signal. Filtering units and amplifiers filter and amplify the signal. The filtered and amplified signals of pulse waves are fed to the inputs of differentiators, where the first derivative of the systolic portion of the pulse wave is isolated. The signals received at the outputs of the amplification units and differentiators are fed to an analog-to-digital converter. The ADC converts analog signals into digital view necessary for the operation of the microcontroller.

Figure 3.4.2 Pulse waves and their differential shape

The microprocessor determines the coordinates of the maximum amplitudes of pulse waves and calculates the value of ∆T:

∆T \u003d T 1 -T 2, (1)

T 1 - the coordinate of the maximum amplitude of the pulse wave obtained by the first sensor 1;

T 2 is the coordinate of the maximum amplitude of the pulse wave obtained by the second sensor 2.

The coordinates of the inflection points (max differential form pulse wave) of the systolic section of the pulse wave and the value of ∆T p is calculated:

∆Т p = ∆Т 1 -∆Т 2 (2)

∆T 1 - the coordinate of the inflection point of the systolic section of the pulse wave obtained by the first sensor 1;

∆T 2 - the coordinate of the inflection point of the systolic section of the pulse wave obtained by the second sensor 2.

The value of the mean arterial pressure (P medium) is inversely proportional to the value of ∆Т:

P medium = F(∆T p). (3)

The value of systolic blood pressure (P syst) is inversely proportional to the value of ∆T p and depends on the stroke volume of the heart:

P syst = F(∆T p). (4)

Diastolic pressure is determined from the formula (P diast):

The performed statistical modeling of pulse wave processing in accordance with the formula made it possible to determine the exact dependencies for P media with a correlation coefficient of 0.95:

P medium = 86.3-0.82∆T for ∆T > 29. (8)

Similarly, dependences for P syst were obtained with a correlation coefficient of 0.89:

According to the table recorded in internal memory microprocessor, are selected in accordance with the obtained values ​​of ∆T and ∆T p values ​​of the mean and systolic blood pressure.

The received data is sent to the internal display and to external device.

The proposed method for determining blood pressure is simple, easy for the patient, because. the measurement time takes no more than 30 seconds.

The device for determining blood pressure is made in the form of an autonomous unit connected by a flexible cable to the sensor unit. It has external connectors for connecting display devices or a PC. At the same time, a diagram of the pulse wave of the examined patient and the values ​​of arterial pressure and pulse can be displayed on an external device.

When using the proposed device in conjunction with a PC, it is possible to significantly expand the range of tasks to be solved.

Figure 3.4.3 Pulse Wave Velocity Output Example

For example, the device, together with a computer and data storage facilities, allows you to take readings quite often and keep detailed statistics on changes in these readings and thus even predict a possible further deterioration in well-being (Figure 3.4.3).
^

4 Structural diagram and description of individual components

4.1 Block diagram

The block diagram shows which elements are used to implement the required functionality.

Figure 4.1.1 Block diagram

Figure 4.1.1 shows the block diagram of the designed device. Let's consider it in more detail.

As a photodetector, a domestic photocell FD256 is used, which has the necessary characteristics and a low price. The signal from the photocells is taken and transmitted to the microcircuits of low-frequency filters.

Since the operation of the device requires the registration of a pulse wave at two points, it is natural that the electronic part of the device before the microcontroller consists of two independent channels, the links in which are completely duplicated.

Low-frequency filter - Butterworth filter implemented on active elements (Figure 4.1.2)

Figure 4.1.2 circuit diagram low pass filter

Filter options:

Cutoff frequency - 20Hz

Transition Width - 100Hz

R1 - 44.8 kOhm

R2 - 44.8 kOhm

R3 - 22.6 kOhm

A detailed calculation of the filter is given below in the relevant section of this work.

To demonstrate the performance of the calculated filter, its circuit was assembled in the Proteus environment and simulated. A sinusoid was used as a useful signal model, and a high-frequency sinusoid was used as noise. As can be seen from the graphs, the low-pass filter brilliantly coped with the task for both channels.

Figure 4.1.3 Low Pass Filter Simulation

Figure 4.1.4 Schematic diagram of the inverting amplifier

The output voltage after the photocell is up to 100mV, therefore, to bring the voltage level to 5V, the gain is 50.

This amplifier was assembled in the Proteus electronics simulation environment. Below are the graphs of its work for two channels, respectively.

Figure 4.1.5 Simulation for a gain link

Figure 4.1.6 Schematic diagram of the inverting differentiator

To obtain the first derivative of the processed signal, a differentiation link is used, made on an operational amplifier chip.

This differentiator was assembled in the Proteus electronics simulation environment to demonstrate its performance. Below are the graphs of its operation and the schematic diagram in the Proteus environment.

Figure 4.1.7 Operation schedules and circuit diagram of the differentiator

Four received signals are fed to the input of the ADC. The built-in 10-bit ADC on the ATmega microcontroller was chosen as the ADC. Its speed and capacity is quite enough to perform all the required operations.

Sampling occurs at a frequency of 20 Hz by interruption from the built-in timer.

Measurement of vital parameters by the microcontroller is performed in the cycle body in the main program every 5 seconds. The results obtained are displayed on the LCD display.

Display MT-10S1 - 10 character LCD display domestic production, described in more detail below.

Also, the received data is sent via the RS-232 port to a computer, where it can be stored, further processed, printed and stored for further analysis.

The DS275 chip is used for level matching. The DS275 chip, manufactured by Dallas Semiconductor, is a TX/RX line-powered RS232 interface driver that is fully compatible with the standard RS232 implementation.

• 
  
• 
  
• 
  

To power the designed device, widely used voltage stabilizers manufactured by National Semiconductor LM78L05, designed for 5 volts, were chosen. Stabilizers are linear voltage regulators of positive polarity.

All operational amplifiers are domestically produced and High Quality. Their characteristics are discussed in detail in the corresponding subsection below.

^

4.2 IR emitter AL107A

Figure 4.2.1 Appearance IR emitter AL107A

Specifications:

• 
  Specifications;
• 
  Maximum reverse voltage 2V;
• 
  Maximum forward current 100 mA;
• 
  Maximum pulse forward current 600 mA;
• 
  Hole mounting;
• 
  Working temperature-60...85 С;
• 
  Radiation power P 5.5 mW;
• 
  Forward voltage 1.8 V;
• 
  at current Ipr. 100 mA;
• 
  Wavelength 953 nm;
• 
  Emission spectrum width 30 nm;
• 
  Visible solid angle 15 deg.

^

4.3 Photocell FD256

Figure 4.3.1 Appearance of photocell FD256

Silicon based photodiode.

Specifications:

• 
  Photosensitive element area (effective) 1.37mm 2;
• 
  Working temperature 20±5 ºC;
• 
  Operating voltage 10 V;
• 
  Spectral sensitivity range 0.4 - 1.1 µm;
• 
  The maximum spectral characteristic is 0.8 - 0.9 µm;
• 
  Dark current no more than 5 nA;
• 
  Integral current sensitivity not less than 0.02 μA/lx;
• 
  Own time constant (U = 10 V) no more than 12 ns;
• 
  Own time constant (U = 60 V), no more than 2 ns;
• 
  
• 
  The case is metal;
• 
  Sensitivity threshold, not more than 1 x 10 -11 lm x Hz-1/2;
• 
  Electrical insulation density, not less than 180 V;
• 
  Entrance window lens;
• 
  Window material glass C52-1;
• 
  Weight, no more than 1 g;

• 
  Temperature range from -60º C to + 85º C;
• 
  Maximum allowable voltage 90 V;
• 
  The maximum permissible illumination is 100,000 lux;
• 
  The failure rate is not more than 3 x 10 -5 h-1 during 5000 hours of operation at a confidence level of 0.6.

^

4.4 KR(KF)1446UDxx series op amp

CMOS op amps are extremely economical, have low input bias current, operate on single or bipolar power supplies, and provide rail-to-rail output voltage. Because of the unique topology that makes these characteristics possible, a new Spice macro model (SMM) was required to get accurate results when modeling circuit designs in CAD.

A very successful SMM CMOS op amp was developed by National Semiconductor, but they do not write models for Russian microcircuits of a similar purpose.

Spice model op-amp series KR(KF)1446UDxx

Product TU Functional analogue	Number of OUs	Frequency Solitary Reinforcements	Large signal amplification	Voltage Offsets	Slew rate V/µs	Quiescent current of one op-amp	Food, V
2-channel universal operational amplifier
KR1446UD1A KR1446UD1B KR1446UD1V	2	1,3	80…96	3,0	1,0	1,1	2,5..7,0
2-channel micropower operational amplifier
KR1446UD2A KR1446UD2B KR1446UD2V	2	0,05	80…96	6,0	0,035	0,013	2,5…7,0
4-channel micropower operational amplifier
KR1446UD3A KR1446UD3B KR1446UD3V	4	0,05	80...96	6,0	0,035	0,013	2,5…7,0
2-channel low power operational amplifier
KR1446UD4A KR1446UD4B KR1446UD4V	2	0,45	80...96	3,0	0,5	0,14	2,5...7,0
2-channel fast operational amplifier
KF1446UD5A KF1446UD5B KF1446UD5V	2	3,6	80...96	3,0	2,7	3,1	2,5...7,0

Spice model op-amp series KR(KF)1446UDxx Continued

Product TU Functional analogue	Number of OUs	Frequency Solitary Reinforcements	Large signal amplification	Voltage Offsets	Slew rate V/µs	Quiescent current of one op-amp	Food, V
2-channel universal high-voltage operational amplifier
KF1446UD11A KF1446UD11B KF1446UD11V	2	1,3	80...96	3,0	1,0	1,1	3,0...12,0
2-channel micropower high voltage operational amplifier
KF1446UD12A KF1446UD12B KF1446UD12V	2	0,05	80...96	6,0	0,02	0,013	3,0...12,0
4-channel micropower high voltage operational amplifier
KF1446UD13A KF1446UD13B KF1446UD13V	4	0,05	80...96	6,0	0,02	0,013	3,0...12,0
2-channel low-power high-voltage operational amplifier
KF1446UD14A KF1446UD14B KF1446UD14V	2	3,6	80...96	3,0	2,7	3,1	3,0...12,0

Figure 4.4.1 Distribution of outputs of the OU series KR(KF)1446UDxx

Figure 4.4.2 Structural diagram of the op-amp of the KR (KF) 1446UDxx series

KR(KF)1446UDxx - a series of CMOS integrated operational amplifiers (op-amps) with an extended range of permissible input (from -U to +UCC inclusive) and output voltages. The series includes 9 OUs: KR(KF)1446UD1/UD2/UD3/UD4/UD5/UD11/UD12/UD13/UD14.

Amplifiers have a wide range of allowable supply voltages. The supply voltage can be either unipolar (-Ucc>0 or +UCC 0). In any case, the voltage Ucc at the +UCC pin relative to the -Ucc pin can vary from +2.5V to +7V for amplifiers UD1, UD5 and from +3.0V to +12.0V for UD11, UD14.

The KR1446UDxx series provides the ability to select an op amp with the required quiescent current per amplifier (10 μA-UD2, 3, 12, 13; 100 μA-UD4, 14; 0.8mA - UD 1, 11; 2.4mA - UD5), which will provide the best for a particular application a combination of dynamic and load characteristics of the OS with a minimum power consumption.

High input impedance (>1000MOm) allows the op amp to work with high impedance sources.

The housing of the integrated circuit contains either 2 identical op-amps (UD1, 11, 2, 12, 4, 14, 5), or 4 0U (UD3, 13) each.

Op-amps are designed to build small-sized blocks of various devices as amplifiers for constant and alternating current, pulse signals, generators, comparators, etc. OS can be used in the construction the following types devices: power supplies, low-frequency active filters, amplifiers with low input currents, hearing aids, microphone amplifiers, picoammeters, integrators, analog-to-digital automation devices.

Specifications:

• 
  Extended range of input and output voltages (from -Ucc to +UCC);
• 
  Wide range of supply voltages (from 2.5V to 7V and from 3.0V to 12.0V);
• 
  Wide choice of quiescent currents of the OS;
• 
  High input impedance (>1000 MΩ);
• 
  Internal frequency correction;
• 
  Construction - 8- and 14-pin DIP or SO plastic package.

^

4.5 Liquid crystal module MT-10S1

The MT-10S1 liquid crystal module consists of an LSI control controller and an LCD panel. The control controller KB1013VG6, manufactured by ANGSTREM, is similar to HD44780 from HITACHI and KS0066 from SAMSUNG.

The module is released from LED backlight. The module allows you to display 1 line of 10 characters. Symbols are displayed in a 5x8 dot matrix. There are intervals between characters that are one display point wide.

Each symbol displayed on the LCD corresponds to its code in the RAM cell of the module.

The module contains two types of memory - codes for displayed characters and a user character generator, as well as logic for controlling the LCD panel.

Figure 4.5.1 Appearance of the MT-10S1 liquid crystal module

The module allows:

• 
  the module has program-switchable two pages of the built-in character generator (alphabets: Russian, Ukrainian, Belarusian, Kazakh and English;);
• 
  Work on both 8 and 4-bit data bus;
• 
  receive commands from the data bus;
• 
  write data to RAM from the data bus;
• 
  read data from RAM to the data bus;
• 
  read state status to data bus;
• 
  display a blinking (or not blinking) cursor of two types;
• 
  control the backlight.

^

4.6 ATmega128 microcontroller

The ATmega128 microcontroller manufactured by Atmel was chosen to control the entire device and exchange data with a PC. These micro controllers have a number of advantages over other micro controllers and circuits based on traditional analog and digital components:

• 
  High performance, low power 8-bit AVR microcontroller;
• 
  Advanced RISC architecture:
  • 
    133 powerful instructions, most of which are executed in one machine cycle;
  • 
    32 8-bit registers general purpose+ control registers built-in peripherals;
  • 
    Completely static operation;
  • 
    Performance up to 16 million operations per second at a clock frequency of 16 MHz;
  • 
    Built-in multiplier performs multiplication in 2 machine cycles;
• 
  Non-volatile program and data memory:
  • 
    Endurance 128 KByte in-system reprogrammable flash memory: 1000 write/erase cycles;
  • 
    Optional boot sector with separate programmable protection:
    • 
      Intrasystem programming with built-in boot program;
    • 
      Guaranteed dual operation: the ability to read while writing;
  • 
    Endurance 4k EEPROM: 100,000 write/erase cycles;
  • 
    Built-in 4 KB SRAM;
  • 
    Optional ability to address external memory up to 64 KB;
  • 
    Programmable program code protection;
  • 
    SPI interface for in-system programming;
• 
  JTAG interface (IEEE 1149.1 compliant):
  • 
    Boundary scanning in accordance with the JTAG standard;
  • 
    Extensive support for built-in debugging features;
  • 
    Flash memory, EEPROM, configuration and security bit programming via JTAG interface;
• 
  Distinctive features Peripherals:
  • 
    Two 8-bit timer-counter with separate prescalers and comparison modes;
  • 
    Two extended 16-bit timer-counter with separate prescalers, comparison modes and capture modes;
  • 
    Real time counter with separate generator
  • 
    Two 8-bit PWM channels;
  • 
    6 PWM channels with programmable resolution from 2 to 16 bits;
  • 
    Comparison output modulator;
  • 
    8 multiplexed channels of 10-bit A/D conversion:
    • 
      8 unbalanced channels;
    • 
      7 differential channels;
    • 
      2 differential channels with selectable gain from 1x, 10x and 200x;
  • 
    Two-wire serial interface, non-byte oriented;
  • 
    Two channels of programmable serial USARTs;
  • 
    Serial interface SPI with support for master/slave modes;
  • 
    Programmable watchdog timer with built-in generator;
  • 
    Built-in analog comparator;
• 
  Special features of the microcontroller:
  • 
    Power-on reset and programmable power-down reset circuit;
  • 
    Built-in calibrated RC generator;
  • 
    External and internal interrupt sources;
  • 
    Six modes for reducing power consumption: idle (Idle), ADC noise reduction, economical (Power-save), shutdown (Power-down), standby (Standby) and extended standby (Extended Standby);
  • 
    Software choice of clock frequency;
  • 
    Configuration bit for switching to ATmega103 compatibility mode;
  • 
    General shutdown of pull-up resistors on all lines of I / O ports;
• 
  I/O and enclosures:
  • 
    53 - programmable input-output lines;
  • 
    64-pin. TQFP package;
• 
  Operating voltage 4.5 - 5.5V;
• 
  Speed ​​gradations 0 - 16 MHz.

The AVR core combines a rich instruction set with 32 universal working registers. All 32 registers are directly connected to the arithmetic logic unit (ALU), which allows you to specify two different registers in one instruction and execute it in one cycle. This architecture delivers greater code efficiency by achieving 10 times the performance of conventional CISC microcontrollers.

The ATmega128 contains the following features: 128 KB read-while-write ISP ROM, 4 KB EEPROM, 4 KB SRAM, 53 universal I/O lines, 32 universal operating registers, real time counter (RTC), four flexible timers -counter with compare and PWM modes, 2 USART, two-wire serial interface oriented to transfer bytes, 8-channel 10-bit. ADC with optional differential input with programmable gain, programmable watchdog timer with internal oscillator, SPI serial port, IEEE 1149.1 compliant JTAG test interface that is also used for onboard debug access and for programming, and six software selectable reduction modes power. Idle mode stops the CPU, while maintaining the operation of static RAM, timer-counters, SPI-port and the interrupt system. The Powerdown mode allows you to save the contents of the registers when the generator is stopped and the built-in functions are turned off until the next interrupt or hardware reset. In Power-save mode, the asynchronous timer continues to run, allowing the user to save the timing function while the rest of the controller is asleep. ADC Noise Reduction mode stops the CPU and all I/O modules except for the asynchronous timer and ADC to minimize impulse noise during ADC conversion. In Standby mode, the crystal/resonator oscillator continues to operate, while the rest of the microcontroller is in sleep mode. This mode is characterized by low power consumption, but at the same time allows you to achieve the fastest return to operating mode. In Extended Standby, the main oscillator and asynchronous timer continue to run.

The microcontroller is manufactured using Atmel high-density non-volatile memory technology. The built-in in-system programmable flash allows program memory to be reprogrammed directly within the system via the SPI serial interface using a simple programmer or a stand-alone program in the boot sector. The boot program can use any interface to load the application program into flash memory. The program in the boot sector continues to run while updating the application section of the flash memory, thus maintaining two operations: read while writing. Due to the combination of 8-bit. RISC Single Chip ISFL CPU The ATmega128 is a powerful microcontroller capable of achieving a high degree of flexibility and effective cost when designing most embedded control applications.

ATmega128 supported full set software and hardware design tools, including: C compilers, macro assemblers, software debuggers/simulators, in-system emulators and evaluation kits.

Figure 4.6.1 - ATmega128 microcontroller pinout
^

4.7 Level converter DS275

The DS275 chip, manufactured by Dallas Semiconductor, is a TX/RX line-powered RS232 interface driver that is fully compatible with the standard RS232 implementation.

Figure 4.7.1 - Pinout of the DS275 chip

The microcircuit was chosen as a level converter, because has a number of obvious advantages:

Powered by RX/TX lines of COM port

Asynchronous Full Duplex Operation

It does not require external elements, such as capacitors, to operate (unlike its analogue - MAX232)

Figure 4.7.2 - An example of enabling the DALLAS DS275 chip

Specifications of the microcircuit:

• 
  Supply voltage - 5/12V;
• 
  Output voltage - ±15V;
• 
  Working temperature range – 0С…+70С.

^

4.8 Stabilizers LM78L05 and LM78L12

Figure 4.8.1 - Pinout of the voltage regulator LM78LXX

To power the designed device, widely used voltage stabilizers manufactured by National Semiconductor LM78L05 and LM78L12, designed for 5 and 12 volts, respectively, were chosen. Both regulators are linear voltage regulators of positive polarity and have similar technical specifications:

• 
  The output voltage changes by ±5% depending on the temperature (see figure 4.8.2);
• 
  Output current - up to 100mA;
• 
  Built-in thermal protection;
• 
  Built-in current limiter;
• 
  Available in various packages (TO-92, SO-8, various SMD packages, etc.);
• 
  Requires no external components;
• 
  Output voltage 5 and 12 V.

Figure 4.8.2 - Temperature characteristic of the stabilizer
^

4.9 Filter calculation

Unfortunately, the signal received from photodetectors is noisy. This noise has two components - photon noise and semiconductor noise - and is high-frequency in nature.

To solve the problem of a noisy signal, a low-pass filter was designed to be located after each of the photodetectors.

As you know, the maximum heart rate is about 200 beats per minute, i.e. up to 4Hz. To improve the measurement accuracy, we will take readings 20 times per second, i.e. the cutoff frequency for the low-pass filter will be 20Hz.

Since the calculation of the filter and the ratings of the components is a simple but painstaking task, which is easy to make mistakes, we used special software developed at the AUTS department to calculate the filter.

Figure 4.9.1 Low Pass Filter Parameters

Figure 4.9.1 shows the parameters of the calculated filter. Since an amplifier is already included in the circuit, the filter is not required additional reinforcement in the transmission region and the gain is set to unity.

Figure 4.9.2 Comparison various types filters

It was decided to use the Butterworth filter, because it allows you to get a very smooth frequency response in the gain region (Figure 4.9.2). The flatness of the cutoff line is compensated by the fact that high-frequency noise still starts at a frequency of about 1 kHz, i.e. they will fade a lot.

Figure 4.9.3 Schematic diagram of switching on the filter section

The calculation program proposed a second-order Butterworth filter, which is easy to implement using just one link, shown in Figure 4.9.3.

Figure 4.9.4 Calculated element ratings

Figure 4.9.4 shows the calculated ratings of the filter elements, reduced to the standard rating range.

R1 - 44.8 kOhm

R2 - 44.8 kOhm

R3 - 22.6 kOhm

Figure 4.9.5 Low Pass Filter Frequency Response

Figure 4.9.5 shows the frequency response of the calculated filter. It is easy to see that the calculated filter fully satisfies the set requirements.

^

5 Development of the scheme of the algorithm and the control program5.5 Algorithm of the function for calculating systolic pressure

Figure 5.5.1 - Block diagram of the systolic pressure calculation function

^

5.6 Algorithm of the display function

Figure 5.6.1 - Block diagram of the data output function on the screen
^

6 Circuit diagram description

In full accordance with the block diagram, below is a description of the individual blocks and elements of the electrical circuit diagram.

The designed device consists of two data transmission channels, a microcontroller with a built-in ADC, an LCD display and a communication port. Each data transmission channel consists of an optocoupler, a low-pass filter, an amplifier and a differentiating link.

^

6.1 Description of individual elements

6.1.1 Analog circuits

XP4 - connector for connecting to two optocouplers

Low-frequency filters are used to cut off high-frequency semiconductor and photon noise from the useful signal received from photocells that are part of optocouplers.

R1, R2, R3, R4, C6, C7, DA1 and R10, R11, R12, R13, C9, C10, DA4 are low-pass filters with a cutoff frequency of 20Hz.

Since the signal received from the photocells has an amplitude of only 100mV, signal amplifiers on operational amplifier chips are used to raise the signal level to 5V.

R5, R6, R7, DA2 and R14, R15, R16, DA5 are amplifiers based on operational amplifier chips with a gain of K=50.

To obtain the first derivative of the filtered signal, a pair of differentiating links is used.

R8, R9, C8, DA3 and R17, R18, C11, DA6 are differentiators with time constant T=0.1

6.1.2 Microcontroller

The ADC built into the microcontroller samples 4 received data streams; the microcontroller processes the received data, calculates the average, diatolic and systolic pressure, as well as the pulse. In addition, the microcontroller produces an indication on the LCD and transmits the received data to the PC through the communication port.

DD1 - microcontroller with built-in 10-bit ADC

Q1 - quartz resonator with a frequency of 20 MHz

C1, C2 - auxiliary capacitors for the oscillatory circuit

^

6.1.3 Communication devices

An LCD display is used to inform the user, and an RS-232 communication port is used to transfer data to a PC.

DD2 - voltage level matching chip for the RS-232 port

XP1 - RS232 communication port connector

XP3 - LCD connector

^

6.1.4 Power circuit

The power circuit provides a stable voltage of 5V to power all active analog and discrete components of the device.

XP2 - connector for connection external source food

DA0 is a voltage regulator that provides power to the device with a voltage of 5V.

Conclusion

In this work, we designed a device for non-invasive measurement
blood pressure and heart rate (pulse). Such
the device allows you to take readings quite often, and in the aggregate
with a computer and data storage facilities - to conduct a detailed
statistics of changes in these indications and thus even
predict possible further deterioration of well-being.
The device can be made on an inexpensive existing element base,
does not require highly qualified personnel, suitable for use
outside medical facilities.

During the design of the device, the knowledge and skills gained over the years of studying the specialty "Automation and Control in Technical Systems" were fully involved.
^

Annex A

The listeg with the task will be inserted here.

And here is the calendar page.

Annex B

Bibliography

1. 
   Novatsky A.A. Electronic abstract for the course "Computer Electronics".
2. 
   J.F. Young Robotics Leningrad, Mechanical Engineering, 1979
3. 
   A. A. Krasnoproshina Electronics and microcircuit engineering Kyiv, Higher School, 1989
4. 
   Denisenko T.A., Tikhonchuk S.T. Guidelines on the use of controllers of the SIMATIC S5 family, OGPU, 1998.
5. 
   Yampolsky L.S., Melnichuk P.P., Samotkin B.B. Flexible computerized systems, Zhitomir, 2005
6. 
   D. Morman, L. Heller Physiology of the cardiovascular system.
7. 
   Mandel W.J. Arrhythmias of the heart. Mechanisms, diagnosis, treatment. In 3 volumes
8. 
   Yakovlev V.B., Makarenko A.S., Kapitonov K.I. Diagnosis and treatment of cardiac arrhythmias.