DIY breathalyzer repair

This rather useful device was made a couple of years ago. Many people get a car license, and one of the many questions drivers immediately face is the safety of driving after drinking a small amount of alcohol.

Thus, this project came to life. The breathalyzer is a scale consisting of eight LEDs (this is not a professional breathalyzer), which show the amount of alcohol vapors exhaled by the user. The circuit was assembled on a Chinese universal circuit board. The MQ-3 alcohol sensor (or rather, the coil located in it) changes the voltage value at its output, which is measured using an analog-to-digital converter that is built into the Atmega328 microcontroller.

While analyzing the data through the microcontroller, the LEDs show the alcohol concentration up to 0.002%. In other words, if the indicator lights up completely - all the LEDs from green to red are on, the amount of alcohol has exceeded the permissible norm for drivers.

The breathalyzer is quite simple, therefore it is suitable even for novice radio amateurs. Here is the code and some pictures.

Quartz is here to set the clock speed of the Atmega to work properly. Note that the sensor needs a short time to warm up, and the program does not take this into account, so you need to wait a little before using it.

At the table for Christmas they began to give each other souvenirs. A great excuse to distract from the meal, alternating with libations and chat, considering and discussing the gifts received. Some of them do happen to be unexpectedly curious and arouse everyone's interest. This time the "hit" was the Chinese keychain - breathalyzer. After all, he is a gift, like an anecdote, especially good if it is in place, in this case it turned out to be at the table, despite the fact that it was intended for a car enthusiast. So even before it came to this review, the breathalyzer was tested and I will tell you that everything was "grown-up". Interested in the result? Please - there were no citizens with an excess of alcohol in blood at the table.

In 2017, in the Russian Federation, the permissible alcohol rate while driving was 0.16 ppm with exhaled air and 0.35 in the blood. This is evidenced by the amendment to the Code of Administrative Offenses in the Russian Federation and the Rules of the Road.

With its shape, the keychain is very reminiscent of a computer mouse, its size is one and a half times smaller (70 x 35 x 20 mm). It is comfortable to hold in your hand.

The buttons for the contours of the body do not stick out and the force of pressing them must be quite sufficient, so that involuntary activation is excluded. All control and information elements of the device are signed. The body is made of fairly strong plastic, the body color is dark (not easily soiled).

It is simply impossible not to look inside such a thing, even at the cost of the risk of a possible failure. Nothing - fix it! We move the cover of the power compartment, take out the batteries, we see four screws, three that we unscrew in the corners and remove the side of the case. Now the fourth screw holding the board, remove it and the bottom of the case is free, except for the remaining sound emitter and display.

Double-sided PCB. You can't call her a simpleton. Quad operational amplifier LM 324, a microcircuit - a drop so beloved by Chinese manufacturers, two smd transistors labeled "J3Y" identified as S8050 and two dozen other electronic components on the one hand, and on the other there is something. One thing is bad - the board is unwashed.

Particular attention to the alcohol vapor sensor.It is clear that the thing requires a careful attitude to itself, the protective mesh can be easily clogged in every possible way, so that without any cover, the device will disappear within a week or two if you carry it in your pocket.

And this (in the middle) is a poorly soldered sensor output in the board. Initially, I was looking for something similar, because there could be no other explanation for the fact that the device recognized all the participants in the festive feast as sober.

I soldered the sensor contacts, washed the printed circuit board with alcohol. After assembly, the breathalyzer began to behave adequately - a pharmacy cotton swab soaked in an alcohol-containing liquid called "Vodka" and brought to the exhalation hole was "noticed" by the device at a distance of 3 cm, which he announced by lighting up a yellow LED, while reducing the distance to a little less than 1 cm, the red LED lit up.

It seems possible, in order to adjust the sensitivity of the alcohol tester, to try to replace the constant resistor with a trimmer in the shown section of the circuit. The fact that the alcohol tester “came to life” after the disassembly and the described manipulations was good, but if you “screw” the sensitivity adjustment to it, it will be a small miracle. True, it was prevented from creating it by the lack of ownership and the price of 400 rubles. The author of the review is Babay iz Barnaula.

The world is changing - the people inhabiting it are changing, although one of the unchanging values ​​for many decades (as long as there is evidence of statisticians - and centuries, while statistics were dormant) is the number of alcoholic beverages consumed per capita.

In any country in the world, this indicator is growing, but at different rates. Russia, as is often the case, is “ahead of the rest of the world” (after, perhaps, Ireland). Drinking alcohol can not always be justified, especially when the consequences concern not only yourself.

However, knowing how topical this topic is in Russia and neighboring countries, I consider it important to highlight some technical aspects of the control (and self-control) of persons in respect of whom it is assumed that they have consumed or could have consumed alcoholic beverages. Of course, the purpose of this study is not to argue about legal regulations or the root cause of a problem.

Below we will consider the technical issues of controlling alcohol vapors (from a person's mouth when exhaling), whatever the causes and consequences of alcoholization of some segments of the population. It is practically important that a radio amateur today can independently make a device for monitoring alcohol vapors (and when installing other sensors with similar parameters, monitor other gases, for example, carbon dioxide or gasoline exhaust). To do this, let's turn a little to the history and technology of production of industrial sensors for various vapors and impurities in the air.

In many European countries (Germany, Finland, Poland), breathalyzers or so-called "alcohol vapor detectors" (Roadtest) appeared on the free sale a few years ago.

Rice. 2.57. Breathalyzer appearance

Of course, these are not professional devices (professional, in particular, special services are equipped, for example, the traffic police), but even these modest devices allow you to identify the "smell" and prevent the unwanted consequences of a driver's error on the road, an accident, or even just save your wallet if In such a situation, a meeting with a traffic police inspector is inevitable.

There are many options for breathalyzers produced by different companies in Europe (there are no similar devices of domestic production on free sale yet). One of them is shown in Fig. 2.57, it was acquired in Finland in 2005.

The principle of operation of the breathalyzer

The device is an analyzer of vapors of alcohol, toluene, xylene and other volatile organic vapors. A removable glass tube is located in the upper part of the device body, which is designed to blow air through a person's mouth.

When the power is turned on with the “Power” button, the liquid crystal indicator on the front panel of the device lights up with flashing digits (readings) 0000% BAC. At the same time, a short beep (peak-to-peak) sounds.

After 1-2 seconds, a second beep (similar to the first) is heard, and the word "wait" (wait) starts blinking on the indicator (below the numbers). During this period, lasting 10-12 s, the sensor heats up and enters the measurement air analysis mode. After that, the third sound signal (similar to the first) indicates that the device is ready for operation (for a stream of received air). In this case, on the indicator (below the numbers) the word "wait" is changed to "ready".

If after the third signal “do not blow into the tube” the device perceives the same air that it has already analyzed and does not find any differences in air composition, it will give a negative verdict within 10-12 seconds (in medicine, a negative result is considered good and does not confirm the diagnosis). This state will be shown on the indicator by the inscription "OFF" (without any sound signals). The auto-off system will turn off the power to the device on its own after another 1.5 minutes. This is necessary to conserve batteries.

The device has a connector for connecting an external constant voltage 12 V, a reset button (for re-checking the test) and an indicator backlight.

If alcohol impurities are found in your breath, the device will display digital readings on the indicator (maximum> 4000 - already a criminal case, when you need to forget about the car) and confirm its research with an endless series of sound signals (peak-to-peak), which can be turned off either by the " reset "(exploration first), or with the" power "button.

The device has a special TGS-2620 type air impurity sensor, which requires a constant stabilized voltage of only 5 V for its efficient operation.

Therefore, such a device can be successfully used autonomously, for example, with batteries such as 4 AAA batteries connected in series, which has earned him a truly great fame. Only the cost is upsetting - almost 50 USD.

The device presented below for self-repetition operates on a similar principle, with the only difference that it does not have intermediate sound signals and digital indication. And it has only two signaling states: "drunk" (the sound lasts until the power is turned off) - "non-drunk" (no sound). In the simpler and less functional version of the alcohol tester, considered below, there is one big plus: the price of parts for its repetition will not exceed 400 rubles.

TGS sensors are so named because the abbreviation stands for "Taguchi Gas Sensor". The discoverer of these sensors and their modifications in 1962 was the Japanese inventor Naoyoshi Taguchi.

Most TGS sensors are made with tin oxide. The resistance of these sensors to direct current in ordinary air is high, and if there are impurities (organic vapors) in the air at the corresponding sensor (they are not universal, the alcohol vapor sensor does not react to freon leakage), the resistance drops sharply. It is logical that if you connect such a sensor to a comparator (voltage comparison device), the latter will react, by analogy with a parametric signaling device, to a change in the resistance of the sensor.

DIY breathalyzer

The alcohol vapor sensor can be assembled by yourself. Based on these calculations, an easy-to-repeat device has been developed and tested to replace the industrial alcohol monitor.

The electrical diagram of the device for monitoring and sound signaling of impurities of alcohol vapors in the air (using an alcohol vapor sensor) TGS-2620 is shown in Fig. 2.58.

Rice. 2.58. Electrical diagram of the device for monitoring and signaling alcohol vapors in the air

When processing the output signal of the sensor, a comparator microcircuit is used, which compares the voltages at its two inputs.The supply voltage for the sensor is supplied to pin 1. The common wire is connected to pin 2. The DA2 comparator is connected to pin 3.

The operational amplifier DA1 with elements VD1, R6, C2, R7, R9 provides a delay of 1-1.5 minutes, which is necessary to eliminate false alarms of the device when power is applied.

The VD1 diode prevents the leakage current of the oxide capacitor C2.

Without this delay, the device can turn on the sound signal for 1-1.5 minutes after power is applied, regardless of the presence of alcohol vapors.

How the device works

The GS1 sensor output signal is taken from set point A in standby mode (when "air is clean"). At that moment,

when the voltage (under the influence of alcohol vapors with a concentration equal to or exceeding the set limit) at point A exceeds the voltage value at the input U0 set by the elements of the external RC-trim, the output signal from the DA1 comparator (its high level) will enable the sound capsule with a built-in generator HA1 ( or another sound / light alarm device connected with correct polarity instead of the HA1 capsule).

The voltage U0 can vary in the range of 2.5-3.2 V at an ambient temperature of + 40 ° C and a relative humidity of 65% and, accordingly, in the range of 1.9-3.1 V at a temperature of -10 ° C.

Without the thermal compensation circuit, the response graph could vary from 600 to 3400 ppm for a given gas concentration of 1500 ppm (at an ambient temperature of 20 ° C and 65% humidity).

Thermistor R1 is used for thermal compensation.

The most significant points are the gas concentration, expressed in parts per million (ppm). That is, for example, a gas concentration value of 20 ppm means an alcohol vapor concentration of 20 × 10L

Table 2.1 Influence of compensating thermistor R1 on measuring gas concentration

An alcohol tester is a device designed to measure the level of alcohol in the human body. Today on sale there is a large assortment of devices of various types and directions, therefore, when purchasing equipment, you should pay attention to many factors of difference. In addition, it is important to decide the frequency and target directivity of the instrument.

Alcohol tester - a device designed to measure the level of alcohol in the human body

The assortment range differs in this way:

Sensor wear is accompanied by replacement or calibration

The models have touch screens. The sensors at the breathalyzer are the working part of the equipment that provides accurate readings. Sensor wear is accompanied by replacement or calibration. The time between calibration depends on the type of sensors, which are:

• electrochemical;
• spectrophotometric;
• semiconductor.

Professional breathalyzers are equipped with electrochemical and spectrophotometric sensors. These are the most accurate, strong and durable accessories that last 6-12 months without calibration.

Important! The mouthpiece is a special tube inserted into the device. It is into the mouthpiece that a person blows to determine the level of alcohol in the air exhaled by a citizen.

Personal breathalyzers are equipped with a semiconductor sensor, which is enough for about 250 tests. On average, the period of use is no more than 7-8 months if used correctly, thus, the sensor on an individual type breathalyzer is replaced 2-3 times a year. Calibration is a process performed both in professional service centers and independently. Models often have test counters, a notification is received about a sensor replacement, or you can see sensor wear. Then you need to open the lid, remove the old sensor and put a new one.

Important! Models with semiconductor testers need to be calibrated at the service center, just like professional models equipped with an electrochemical sensor.

The use of the device for individual purposes implies the purchase of a tester of an inexpensive price and with a durable sensor.

The use of the device for individual purposes implies the purchase of a tester of an inexpensive price and with a durable sensor. It is the price that determines the reliability, durability of the device and the accuracy of the readings. Too cheap models cannot be calibrated and replaced - they are disposable testers. They are used no more than 1 time per day and are thrown away if the settings fail.

Important! When purchasing the device, you need to pay attention to the possible service. Very often there are high-cost models on the market, the calibration of which is impossible only due to the lack of service repair. It will be unpleasant to learn about this feature after purchase and use.

The second point is ease and convenience of use. The presence of a mouthpiece is an optional rule, but here you need to check the accuracy of the results. It is very important not to fall for a fake tester - these are models offered via the Internet or resellers at a very low price. As a rule, a "gray" tester has no warranty, is not accepted for calibration and is not repaired even in private services.

The use of a breathalyzer is determined by the need. The scope of use is wide:

• production;
• checking motorists on the roads;
• examination in medical institutions;
• individual use.

Important! Devices without the need for calibration often fail in readings, so buying this device may turn out to be unprofitable - the tester will not "let" you drive, even with complete sobriety.

Semiconductor sensors have the functionality of triggering against the ingress of alcohol vapors on them

1. Semiconductor sensors have the functionality of triggering against the ingress of alcohol vapors on them. The measurement result is displayed on the screen, but the sensing element often needs to be replaced. Sensitivity of sensors is reduced by 25%, unlike other sensors.
2. Electrochemical breathalyzers work when the reagent contained in the device interacts with alcohol vapor. After the analysis is carried out, the result is displayed on the screen. The readings are highly accurate, the device itself with a similar sensor is often used for examining citizens by police officers and in medical institutions.
3. Photometric sensors have the functionality of triggering when the properties of the luminous flux change when passing through alcohol vapor. These are expensive instruments intended for professional use only and are characterized by high accuracy of readings, long service life without calibration and the ability to carry out a large number of tests per day.

When choosing a device, you should pay attention to the presence of a mouthpiece

Important! When choosing a device, you should pay attention to the presence of a mouthpiece. Mouthpieceless models have increased measurement accuracy, but are more expensive than mouthpiece counterparts.

Alcohol tester models often have additional features:

1. Saving data to other media / gadgets;
2. Incomplete expiration signal;
3. Emergency charging, memory function;
4. Display of data by sound or light signal;
5. Metric screen;
6. Synchronization of readings with a memory block.

The latest models are especially convenient, since when replacing the sensor, there is no need to restore the factory-type calibration parameters - they are saved automatically.

IMPORTANT. The information presented in the material is for informational and informational purposes only. And it is not an instruction for action. A mandatory consultation with your attending physician is required.

Russian legislation quite rightly follows the path of toughening measures of responsibility for those who threaten road safety. The formal requirements for persons driving a vehicle are also increasing: the previously permitted alcohol content in the lung sample - 0.3 ppm - in 2016 was reduced to 0.16 (in the blood - to 0.35 ml / l).Nevertheless, since the devices that allow determining the amount of alcohol in the body have appeared in the arsenal of the traffic police, drivers have been wondering how to deceive the breathalyzer and whether it is possible to do it in principle. However, this is also curious for sober pedestrians. What is a modern breathalyzer and are there ways to influence its readings?

Even 10 years ago, cheating a breathalyzer was a relatively feasible task. Someone tried to hold their breath, someone tried to exhale past, especially smart ones plugged the opening of the device with their tongue, diligently puffing out their cheeks and imitating a conscientious exhalation. Today, such manipulations are unlikely to be crowned with success, since a modern alcohol meter will immediately let you know about an insufficient volume of air for analysis.

An electronic device that records the concentration of alcohol in the exhaled air consists of a tube, a chamber, an analyzer and an indicator, where the measurement result is displayed. As a result of heating, the air entering the chamber is converted into steam, which acts on the analyzer. In this case, the electrochemical sensor detects precisely the alcohol molecules, taking into account their content per unit volume.

The device is equipped with a buzzer indicating readiness for work, air intake in the required volume and exceeding the alcohol threshold.

If alcohol was taken immediately before testing, the device will record it “in its pure form”. After about 15 minutes, alcohol molecules enter the bloodstream from the digestive system, and the breathalyzer already reacts to the alcohol content in the air from the lungs.

Thus, the device can be misled within 10-15 minutes, when the mouth after a couple of minutes is already "clean", and the concentration of "doping" in the blood has not yet reached critical levels. But, you must admit, it is unlikely to meet with the inspector in such a limited period of time, and the aroma of recently taken alcohol will inevitably darken the joy of the meeting.

The popular methods of eliminating the signs of alcohol intoxication can be divided into three groups.

1. Means that slow down the absorption of alcoholic beverages into the bloodstream from the gastrointestinal tract (fatty foods and vegetable oil).
2. Methods that enhance metabolism and accelerate the elimination of alcohol decomposition products from the body (physical activity, bath procedures, drinking plenty of fluids).
3. Masking tricks (various products that have a deodorant and refreshing effect).

Let's take a closer look at the most popular folk methods.

Vegetable oil really envelops the mucous membranes of the digestive system, preventing the intense flow of alcohol into the blood, but this period can be extended by no more than half an hour. This method is partially justified if a small amount of alcohol was taken at the same time and it is planned to get home within half an hour.

Fatty foods in large quantities have a similar enveloping effect. In addition, due to the fact that the enzyme system works hard to break down complex fats, the rate of alcohol absorption is somewhat reduced. However, contrary to the existing myth, oil and fats do not bind alcohol molecules and do not remove them from the body naturally in an unchanged form. Alcohol is still absorbed and is present in the exhaled air for up to 10 hours.

Both methods are applicable only in the case of mild alcohol intoxication and are based on stimulating metabolism and speedy elimination of alcohol markers from the body, mainly due to intense sweating.

The bathhouse or sauna must be warmed up enough to stay inside for no more than 5 minutes. After each call, the waste products should be washed off the skin. The disadvantage of the technique is that it is quite lengthy in time. So, in order to remove the alcohol contained in a liter of low-alcohol drink from the body, it will take 2-3 hours for a bath procedure.

Of physical exercises, running, swimming, push-ups, pull-ups on the horizontal bar are effective - in a word, everything that makes a person sweat properly.

Many are interested in whether it is possible to deceive a breathalyzer by abundantly absorbing water and soft drinks. Drinking pure water, especially acidified with lemon juice, really reduces the level of intoxication in the body. However, about 90% of alcohol is excreted through the liver, so the method does not guarantee a significant decrease in the concentration of alcohol in the blood, and therefore in the air leaving the lungs.

Such techniques are aimed at eliminating the smell of alcohol and increasing the overall tone. Chewing coffee beans, parsley leaves, bay leaves or cloves will temporarily eliminate the characteristic smell of alcohol, but will in no way affect the readings of the breathalyzer. Powerless against the unforgiving device and mint chewing gum, and deodorants for the oral cavity. You should be especially careful with the latter, since many of them contain ethyl alcohol.

A sufficiently effective way to influence the verdict of an alcoholic is considered to have drunk a cup of coffee or strong tea a minute before testing, but doing such a trick in front of a traffic police officer is quite problematic. The advantage of the listed manipulations is that they help to cheer up, increase concentration, visually seem sober and thus lull the guard's vigilance.

Hyperventilation of the lungs, that is, several forced inhalations and exhalations immediately before testing, can lower the breathalyzer reading by 10-15%. At the same time, holding the breath, on the contrary, increases the measurement result of a modern electrochemical device. In addition, the device can respond to a lack of air volume. The intermittent breathing technique, when the exhaled air stream is mixed with the air of the street, helps to reduce the readings of the breathalyzer. The difficulty in implementing both techniques lies in the fact that they have to be applied under the watchful eye of the representative of the law.

We note right away that a magic pill that eliminates the effects of abundant libations has not yet been invented. Widely advertised today drugs from the category of "Antipolitsay", allegedly allowing to eliminate alcohol from the body in 2-3 hours, in fact, contain components that reduce headaches, vitamins and flavorings. The role of such drugs in the elimination of alcohol is insignificant. A similar symptomatic remedy is Alka-Seltzer and other aspirin preparations.

The preliminary intake of activated carbon (1 tablet per 10 kg of body weight) reduces the manifestations of intoxication syndrome, but does not contribute to a significant decrease in blood alcohol levels.

The most effective of the existing procedures for detoxification of the body is a dropper with glucose, vitamins C and group B. But setting it outside the walls of a medical institution is difficult.

Obviously, the easiest and most reliable way to cheat a breathalyzer is not to drive drunk, even if it seems that you have drunk a little. After all, the presence of alcohol in the blood reduces attention, disrupts the coordination of movements, lowers visual acuity. A breathalyzer is a high-precision and impartial device designed to stop a careless driver and prevent tragedy.

If you are the owner of such a useful and somewhat unusual device as a breathalyzer, which in modern society can be useful at the most unexpected moment. Its main purpose is to measure the amount of alcohol vapors in the exhaled air of a person, and by their concentration, the device shows the corresponding value, on the basis of which one can judge the degree of intoxication. Such a device can be useful if a disputable situation arises with a traffic policeman, or in cases where you are not entirely sure whether you should drive your car in the morning after yesterday's feast. But like any device, the breathalyzer can break.

If such a situation arises, it is best for you to seek help from professionals who specialize in the repair of such devices. However, for your awareness, it is worth remembering that breakdowns of the breathalyzer can be caused by both objective reasons and quite common ones.

The main reason for the breakdown, if you can call it that, is an error message during the next test, or you understand that the device's indicators do not correspond to reality. In this case, it can be argued that the sensitive sensor of the device, which is responsible for detecting and registering the content of alcohol vapors in the air, is out of order. This can happen if the sensing element becomes dirty over time, or if the device is tested immediately after drinking alcohol. This should not be done under any circumstances, as fresh vapors of alcohol from your mouth can burn or damage the sensor. The measurement should be made only after 20 minutes from the moment of the last intake of alcohol, otherwise the sensor will need to be replaced.

In the event of a normal breakdown, be it damage to the case due to mechanical damage or failure of any microcircuit or device display, these elements must be replaced in the workshop.

Breathalyzer or breathalyzer - this device is used to assess the concentration of alcohol in the exhaled air of a person. The measurement results indirectly determine the amount of alcohol in the driver's blood. This electronic device is commonly used by gay people and medical personnel. However, the breathalyzer circuit will also be useful for motorists to correctly assess their own condition.

The alcohol vapor sensor can be assembled by hand based on the TGS-2620 sensor. To process the output signal from it, the DA2 K554SAZ comparator is used, the supply voltage is supplied to the first output, to the second common wire. The comparator is based on the classic circuit for comparing two input signals. The comparator input is connected to the third terminal of the sensor. OA DA1 with elements VD1, R6, C2, R7, R9 implements a delay module of 1 - 1.5 minutes, which is necessary to eliminate false alarms of the structure when the supply voltage is applied. The VD1 diode prevents the leakage current of the capacitance C2. Without this delay, after power-up, the circuit can beep regardless of the presence of alcohol vapors.

For light indication), parallel to the HA1 capsule with a built-in ZCh generator, an LED with a series-connected resistance of 470 - 750 Ohm is connected.

Instead of TGS-2620 in this design, you can use sensors TGS-880, NGS-2181 from Murata.

Take into account the testimony of your breathalyzer with your own hands, they mean nothing to the traffic cops. I recommend making the printed circuit board according to the new radio amateur technology LUT

Do-it-yourself breathalyzer on Arduino is very easy to assemble yourself. It consists of an Arduino controller and an MQ-3 alcohol sensor, which can be found at the world's flea market at very cheap prices. Five LEDs are used to indicate the concentration of alcohol vapor in the exhaled air. They are connected in series with resistances with a nominal value of 220 ohms to limit the current. These components are connected to the digital port of the Arduino board (lines D0-D9). Diy breathalyzer connection diagram is shown below.

The MQ-3 is an alcohol sensor used to measure the amount of alcohol in exhaled air. This transducer is specially designed for alcohol detection, so it has a good alcohol sensitivity. It is also capable of detecting gasoline, but its sensitivity is much worse in this case. The MQ-3 has 6 pins, of which two activate the heating element, and the remaining 4 provide signaling and power to the circuit.

We connect the AD0 MQ-3 pin to the analog input A0 of Arduino, from which we read information about the alcohol concentration.The sensitivity of the circuit is adjusted using a variable resistance on the MQ-3 sensor module.

Breathalyzer repair, calibration and sensor replacement. (To specify the cost of repairs by phone)

This process is the adjustment of the device in order to bring its measurements according to the standard (a technical tool that adjusts the exact value in the desired units). Calibration is carried out by a specialist using a calibrator within fifteen minutes. Unlike professional instruments, which are designed for a significant number of tests, simpler personal instruments require calibration more often.

How much calibration is necessary?

There are several types of sensors. Inexpensive semiconductors commonly used by individuals. These devices are more likely to break down due to violations of the operating rules. They are designed for 200-300 measurements, after which they must be taken to the service center (except for those that are initially equipped with a spare sensor). More accurate sensors are electromechanical, the number of measurements is up to 1000. These are devices for professional use, they need to be calibrated 1-2 times a year.

In a service center, calibration can be done in two ways:

• wet bath - using an alcoholic standard poured into the measurement equipment. This method is distinguished by increased accuracy of testing and adjusting the breathalyzer;
• dry gas - using an air mixture of nitrogen and ethanol. This method allows you to calibrate the instrument in any room.

It is important to remember that all breathalyzers lose sensitivity over time, and this affects the readings. The main reason is sensor contamination.

The sensor is the main sensor of every breathalyzer, thanks to which the level of ethanol vapors is determined. During testing

the sensitive surface heats up, which over time reduces the accuracy of readings along with particles of dust and saliva. Some models

In order for the device to work correctly, it is necessary to carry out quarterly preventive maintenance. Our service center offers maintenance and warranty repair of breathalyzers by qualified specialists at affordable prices. Alcometers are equipped with an additional sensor that you can replace yourself. However, this is not recommended as new sensors are generally not calibrated. To avoid this, it is best to replace the sensor at a service center. For the rest of the breathalyzers, the sensor can be replaced only at the service center. Replaced the sensor and use the device as if it were new.

Our contacts:

Moscow, metro “Ulitsa 1905 Goda”, Zvenigorodskoe shosse, 4, TC “Electronics on Presnya”, pav. B-31

The alcohol vapor sensor can be assembled by yourself.

The electrical diagram of the device for monitoring and sound signaling of impurities of alcohol vapors in the air (using an alcohol vapor sensor) TGS-2620 is shown in Fig. 2.19.

Rice. 2.19. Electrical diagram of the device for monitoring and signaling alcohol vapors in the air

When processing the output signal of the sensor, a DA2 comparator microcircuit is used, which compares the voltages at its two inputs. The supply voltage for the sensor is supplied to pin 1. The common wire is connected to pin 2. The DA2 comparator (K554SAZ microcircuit) is switched on according to the classical scheme for comparing two input signals, one of which should have greater stability. The comparator input is connected to pin 3 of the GS1 sensor.

The operational amplifier DA1 with elements VD1, R6, C2, R7, R9 provides a delay of 1-1.5 minutes, necessary to eliminate false alarms of the device when power is applied.

The VD1 diode prevents the leakage current of the oxide capacitor C2. Without this delay, within 1-1.5 minutes after the devices are powered on, they can turn on the sound signal, regardless of the presence of alcohol vapors. The GS1 sensor output is taken from set point A.

In standby mode, when the air is "clean", at the moment when the voltage (under the influence of alcohol vapors with a concentration equal to or exceeding the set limit) at point A exceeds the voltage value at the input U0 set by the elements of the external RC-trim, the output signal from the comparator DA1 (its high level) will ensure the activation of a sound capsule with a built-in HA1 generator (or another sound / light alarm device connected with the correct polarity instead of the HA1 capsule).

The voltage U0 can vary in the range of 2.5-3.2 V at an ambient temperature of +40 ° C and a relative humidity of 65% and, accordingly, in the range of 1.9-3.1 V at a temperature of -10 ° C.

Without a temperature compensating circuit, the response graph could vary in the range of 600-3400 ppm at a given gas concentration of 1500 ppm (at an ambient temperature of +20 ° C and a humidity of 65%). Thermistor R1 is used for thermal compensation.

The results of using a temperature compensating resistor are presented in table. 2.2.

Table 2.2. The influence of the compensating thermistor R1 on the measurement of the gas concentration in accordance with the electrical diagram in Fig. 2.19

The amount of alcohol consumed “per capita” (more precisely, per body) is in some cases very critical (for example, for drivers). In many European countries (Germany. Finland. Poland, etc.) a few years ago, detectors of alcohol vapors, or the so-called “breathalyzers” (Roadtest), appeared on the free sale. Of course, these are not professional devices, but they also allow you to control the “smell” and assess your condition after taking something “warming”. Breathalyzer options. there are many produced by different firms, but there are no similar domestic-made devices on free sale yet.

A typical circuit for switching on the sensor is shown in Fig. 4. If you connect such a sensor to a comparator (comparator), the latter will react to a change in the resistance of the sensor and turn on the alarm. For efficient operation of the sensors, a constant voltage of about 5 V is required. Therefore, such a device can be successfully used with an autonomous power supply, for example, from 3-4 miniature AAA batteries. The only disappointing thing is the cost of the sensors - almost 50 USD. The proposed device operates according to a similar principle, with the only difference that it does not have intermediate sound signals and digital indication, but shows only two states: drunk (the sound lasts until the power is turned off) or not drunk (no sound). The diagram of the “Breathalyzer” using the TGS-2620 sensor is shown in Fig.5.

The issue of controlling the content in the air of carbon monoxide, carbon dioxide and many other volatile substances, including alcohol vapors, is very relevant. This could often prevent accidents at home and at work. Numerous gas detectors are used to detect various contaminants.

The principle of operation is the same for all gas sensors. Structurally, the sensors contain a gas-sensitive element. When exposed to specific gases, the resistance of the sensor changes. To improve the efficiency of the sensor, it is heated using a heating element located inside the gas sensor. The change in resistance of the sensor with fluctuations in gas concentration is the response of the sensor. Depending on the dopants in the heated element (sensor), a high sensitivity to certain gases can be obtained. Initially, the heating element was a spiral, like in an incandescent lamp. Later, the entire structure became thick-film. This made it possible to achieve not only a decrease in labor costs for the manufacture of sensors, but also to ensure the identity (repeatability) of their parameters.

Gas sensors are produced by many foreign companies, such as the Japanese company "FIS", the German "Sensoric", the English "City Technology". For example, the Japanese company "Figaro Engineering Inc." has been producing such sensors for more than forty years. At the same time, more than 1 million pieces of sensors are produced per month.They are designed for household gas leak detectors in homes, for monitoring ventilation systems and air conditioning. About 15% are used for climate control of car interiors and the presence of explosive gases in them. These sensors are used by many world leaders in the automotive industry - "BMW", "General Motors" and others.

We will turn our attention to alcohol vapor detectors. The author of the article [1] wrote that if a radio amateur has a TGS-2620 or TGS-822 sensor of the Japanese company "Figaro Engineering Inc." it is easy to make the simplest breathalyzer for “household” needs. Crafting is always interesting and if you managed to get it, then it's worth trying.

Unfortunately, some aspects of the construction of the circuit [1] had fundamental technical inaccuracies, which required elimination of errors. For the convenience of readers, the diagram [1, Fig. 2] is repeated in Fig. 1 of this article.

The history of the appearance of these errors and their duplication in the technical literature is interesting. It should be emphasized that errors in the principle diagram of the breathalyzer have appeared in print media and the Internet for a long time. Since then, they have been duplicated many times. In particular, looking through the Internet materials of companies that sell TGS gas sensors from Figaro Engineering Inc., you can find a typical connection diagram for a sensor of the TGS 8 xx and TGS 2 xxx series - fig. 2.

It was hard to believe that the error came from the site of the gas sensor manufacturer "FIGARO". It turned out that in the materials [2] on her website there was no error in the scheme (Fig. 1 4) (Fig. 3).

At the same time, the diagram shows the unit for the delay in turning on the gas tester after its power supply (Fig. 1 8). As you can see, the main difference is that the operation of the comparator should be blocked at the non-inverting input. This is provided that in these circuits, the connection of the "Buzzer" sound emitter to the output of the comparator through a matching transistor is performed identically.

Consider the circuit in Fig. 1. The sensor is usually connected directly to a voltage comparator. In the diagram in Fig. 1 is a K554SA3 microcircuit. It is well known that at pin 9 it has an "open collector" of the output transistor. The emitter of this transistor (pin 2) is connected to the minus of the power supply of the circuit. The base of the transistor VT 1 is connected through the resistor R 8 only to pin 9 (OK) DA1, therefore, in this circuit, the bias is not applied to the transistor and is not removed from it. So the transistor cannot be controlled. To “remove” the offset, it must first be submitted. To do this, for example, you need to connect pin 9 DA 1 not only to R 8, but also to the resistor R 6, as shown in Fig. 4. The other terminal of the resistor R 6 is connected to the “plus” of the circuit power supply. In practice, this is done in practice in most circuits where the K554SA3 microcircuit is used.

The value of the resistor R 6 is not critical. When prototyping the circuit, 5.1 resistors were used. 20 kΩ, however, adding a resistor R6 to the circuit will make it possible for the DA1 comparator microcircuit to work, but not the breathalyzer circuit in Fig. 1.

The time relay on the DA 2 microcircuit is designed to block the DA1 comparator, as noted by the author [1], for 1. 1.5 minutes. During this time, the GS 1 alcohol vapor sensor must be prepared for operation (warmed up) after switching on the circuit power.

Indeed, after turning on the power of the circuit, the capacitor C2 of the timer DA 2 is discharged and a high potential is set at the output 6 DA 2, close to the value of the supply voltage of the microcircuit. This voltage is applied to the inverting input (pin 4) of the DA1 microcircuit, blocking the breathalyzer. It is noteworthy that in scheme [1] the timer blocking time by 1. 1.5 minutes is unreasonably overestimated. In the FIGARO circuit with the same capacity of the timing capacitor of the timer (220 µF), the value of the resistance of the timing circuit resistor is not 1.5 MΩ, but 750 kΩ. This reduces the quality requirements for this electrolytic capacitor.

After the end of the time delay, the state of the DA 2 microcircuit is reversed. At its output, a “zero” potential appears, but in the circuit in Fig.1, this leads to a malfunction of the breathalyzer - regardless of the output signal of the GS 1 sensor, a signal that the permissible concentration of alcohol vapors is exceeded instantly sounds. The circuit (Fig. 1) requires adjustment.

There can be many ways to fix the error to restore the functionality of the circuit. In fig. 4 shows how the operation of the HA1 emitter can be blocked while the GS 1 sensor is warming up due to the influence of the DA 2 timer directly on the key transistor VT1.

The timing chain R11, C2 is connected to the non-inverting input of the operational amplifier DA 2, and during the time delay at the output of the microcircuit (pin 6) there will be zero potential. The bias to the base of the transistor VT 1 is not applied for this time and it is in the locked state. Diode VD 2 - decoupling. It excludes the influence of the DA 2 microcircuit on the operation of the VT 1 transistor after switching the timer. The type of diode is not critical. A diode can be used, for example, KD521 or KD522.

In the article [1], an erroneous interpretation of the purpose of the diode VD1, shunting the resistor R 6, was given: “The diode VD1 prevents the leakage current of the oxide capacitor C2”. Physically, during the operation of the circuit, the VD 1 diode is locked by reverse bias on it and does not participate in the work. When you turn off the power to the circuit through this diode, the capacitor C2, charged during the operation of the circuit, is very quickly discharged. This ensures that each new cycle of the circuit after turning on its power begins with the same time delay used to warm up the GS1 sensor.

The prototyping of the circuits showed that the value of the resistor R 6 (Fig. 1) and R11 (Fig. 4) can be significantly reduced. This will help reduce the requirements for the quality of the capacitor C 2. The capacitance of the capacitor in this case, of course, must be increased.

Features of the output stage of the K554SA3 microcircuit (pin 9 - “open collector”) allow to further simplify the breathalyzer circuit - fig. 5.

In it, the output of the DA 2 microcircuit (pin 6) is connected to the base resistor R 7 of the transistor VT 1 through a decoupling resistor R 6. When the power is initially turned on, the DA 2 pin 6 is at zero potential. Accordingly, there will be a zero potential based on the transistor VT1. After the timer has worked off DA 2, the potential of its output will become unitary, but whether this potential arrives at the base of the transistor VT1 will depend on the state of the output transistor of the DA1 comparator microcircuit.

When repeating the breathalyzer circuit, one should not forget that the HA1 emitter for the circuits must contain a built-in signal generator. In fig. 1 indicates its type KP1 -4332. It was not possible to find one on sale, and when testing the circuit, it was replaced by a similar emitter with a built-in generator - KPX -1205V. Its supply voltage is 5 V, and the KPH-1212V is 12 V.

Looking through the reference materials on the FIGARO sensors, it is striking that the numbering of the terminals of the TGS-2620 sensor in [1] does not correspond to the data of the company "FIGARO". In fig. 4 and fig. 5 of this article, the connection of the GS 1 sensor is made in accordance with the proprietary reference materials of this sensor. The appearance and dimensions of the TGS-2620 sensor are shown in Fig. 6 and fig. 7.

In conclusion of the review, I want to draw the attention of readers to the need to set the threshold for the operation of the breathalyzer circuit when setting up. This is not provided in the scheme [1], but it is extremely necessary. In the diagram in Fig. 2 this function is performed by the trimming resistance R L. In the diagrams in Fig. 4 and fig. 5 trimming resistance R 5 sets the potential of the inverting input of the comparator DA1. It is safer for the GS 1 sensor compared to the diagram in fig. 2, since according to TU, the permissible dissipation power of the measuring resistance of the RS sensor is not more than 15 mW.

In contrast to the diagram in Fig. 4 in the diagram of Fig. 8 the polarity of the output signal of the turn-on delay timer is reversed. For this, the timing capacitor C2 is connected to the non-inverting input of the DA2 microcircuit.

When the power is turned on, the capacitor C2 begins to charge, and at the output (pin 6) of the DA 2 microcircuit, a single positive potential is maintained all this time. Through the diode VD 2, it is fed to the inverting input of the comparator DA1. Regardless of the output signal of the GS 1 gas sensor, during the pause time after turning on the power, the output transistor of the DA 1 microcircuit will be open. This removes the bias from the base of the transistor VT 1 and it will be in a non-conducting state.

After working off the pause, the DA 2 microcircuit, its output signal will become zero, but the VD 2 diode will prevent it from passing to the inverting input of the DA1 comparator.

Scheme fig. 9 contains the minimum number of parts. It is built on just one microcircuit (DA1) of the K554CA1 type. It uses the fact that its output transistor operates in the "open" collector mode at pin 9. The bias to the transistor VT 1 is fed through the resistors R 5 and R 6 only if the output transistor of the microcircuit is open. The offset from the base of the transistor VT 1 is removed and it is locked.

After the end of the pause, the capacitor C2 will be charged and the potential of the inverting input of the comparator DA 1 will be determined only by the value of the resistors R 1. R 3.

If a non-specialized comparator microcircuit, a standard operational amplifier is supposed to be used as a DA 1 chip for the delay unit for switching on the breathalyzer after power is applied to the circuit, then it is imperative to provide for the decoupling of its output in the circuit. There are practically no “open” output operational amplifiers on the market. Such op amps are not even found in reference materials on microcircuits or on the Internet, although there you can find a lot of interesting and instructive things, for example, article [3], get some information from other sources [4. 5]. Some new schemes are also given in [6].

In conclusion, it should be noted that non-traditional use of breathalyzers based on Figaro sensors is also possible. If the inverting and non-inverting inputs of the DA1 comparator are reversed in the circuits, then when the concentration of alcohol vapors in the air is less than the established norm, the sound signal of the HA1 emitter will sound, and when the alcohol concentration exceeds its norm, the sound signal will stop. Such a breathalyzer will be a funny toy at a friendly feast. He will immediately show who is gaining their "degrees" with us, and who is only imitating it.

For such a modification of the breathalyzer, it is enough to swap the inputs of the comparator DA 1 in the circuit using the double switch SB 1 - fig. 10.

We get two modes of operation of the breathalyzer - standard and comic. Having calibrated the scale of the adjusting resistance of the breathalyzer, it is possible to quite accurately determine the excess of the “norm” on its scale and state the magnitude of this excess. This is already a "formidable weapon" in the hands of our wives!

1.Andrey Kashkarov. Alcohol vapor sensor. Radio amateur. -2008. -№1 -С.7-9.

3. Yuri Koval. Sensors The world of automation. -2006. -June. -S.18-23.

4. Semiconductor alcohol vapor sensor MQ -303A // Radio circuit. -2008.№6. -S.2-3.

5. G. Dioszegi. Gas detector (CO and alcohol vapors) // Radiotechnika. -2005. - No. 11

6. E.L. Yakovlev. Gas sensors and their application // Radioamator. -2009. -№7/8. -S.32-35.