WHEN YOU CAN SIT BEHIND THE WHEEL

Recently Russia adopted a law allowing drivers to get behind the wheel of a car with a small residual content of alcohol in the blood. Knowing how topical this subject in Russia, I think it is important to highlight some technical aspects of control (and self control) persons who consumed alcohol. Of course, the objective of this study is not in dispute is that the law or the causes of the problem. Below we consider the technical issues on breath alcoholic couples. But first, let’s look at the history and production technology of industrial sensors of various vapor and impurities in the air. In many European countries (Germany, Finland, Poland and others) a few years ago appeared in the free sale breathalyzer, or so-called “alcohol vapor detectors” (Roadtest).

Of course, this is not a professional instrument (professional, in particular, equipped with special services, such as traffic police), but these modest devices allow to identify the degree of concentration of alcohol in blood for self-monitoring of the driver to prevent unwanted consequences on the road.

Options of breathalyzer, manufactured by different companies, in Europe a lot. One of them is in the photo, he acquired in Finland in 2005.

Similar devices of domestic production available for sale yet, but ham radio today is able to make a device for control of vapors of alcohol (as with the installation of other sensors with the same parameters to control and other gases, e.g. carbon dioxide or exhaust gas).

The principle of operation of the breathalyzer

The device is an analyzer of alcohol vapors, toluene, xylene and other volatile organic compounds. In the upper part of the housing of the device has replaceable plastic tube designed for receiving blown air man.

At power on press Power aktiviziruyutsya LCD display on the front panel of the device with blinking digits (readings) 0000% YOU. At the same time hear a short audio signal (peak-to-peak). After 1 — 2 dealt with the second, and the indicator light (beneath the numbers) starts flashing the word wait (wait). This period of 10 — 12 is entering the sensor mode the air.

After that third beep (similar to the first) indicates that the device is ready for operation. In this case, the indicator light (beneath the numbers), the word is replaced by wait for ready.

Breathalyzer from Finland

If after the third signal “is not to blow into the tube” the device will perceive the same air which he had already analyzed, and, not finding differences in the composition of the air, for 10 — 12 will give a negative verdict (in medicine a negative result is considered good, not confirming the diagnosis). This condition will be shown on the display the inscription OFF (without any beeps). System auto off will shut off the power to the instrument on their own after another 1.5 min. This circumstance you need to conserve batteries.

The device has a connector for external DC power supply 12, a reset button (to cross-check test) and highlight indicator.

If your breathing is detected admixture of alcohol, the device will show on the display a digital readout (max >4000 is already the case when we need to forget about the machine) and confirm his study of infinite series of audible signals (peak-to-peak), which can disable will be either the reset button (first study) or the power button.

The device has a sensor impurities in the air of the type TGS-2620, for efficient operation which requires DC stabilized voltage of 5 V. Therefore, this device can be used autonomously, for example, with batteries of 3 or 4 batteries, connected in series, which significantly increased its attractiveness. The only minus is the price — about 50 $ USD.

On a similar principle operates is presented below the author developed a device with the only difference that an intermediate sound signals and the digital readout had not. The device has only two alarm States: drunk (the sound lasts until the power is turned off) — not drunk (no sound). In a more simple and less functional version of alcohol tester, discussed below, has one big advantage: the price details for its repetition does not exceed 400 rubles.

Practical application in Amateur radio designs popular sensors alcohol (alcohol vapor) of the type TGS-822 and TGS 2620 Figaro Engineering Inc. (Japan).

Abbreviation TGS stands for Taguchi Gas Sensor. The discoverer of these sensors and their modifications in 1962 became a Japanese inventor Naoyoshi Taguchi.

Most of the sensors TGS made on the basis of tin oxide. The resistance of these sensors DC in normal air high, and in the presence of air contaminants (organic vapors) from the appropriate sensor (they are not universal, a sensor of alcohol vapors does not respond to a freon leak) resistance is sharply reduced. If you connect such a sensor to a comparator (device comparison voltage), the latter reacts by analogy with parametric alarm to change the sensor resistance and include audio (and other) signaling. Based on these calculations was developed and tested in the repetition of a simple device that replaces the industrial control device of alcohol.

Breathalyzer with your hands

A sensor of alcohol vapors can be collected and independently. The electrical circuit of the control device of impurities the alcohol vapors in the air and the chime application of sensor TGS 2620 is shown in Fig.

When processing the sensor output signal is a chip-DA2 comparator that compares the voltage at its two inputs. The voltage supply for the encoder is supplied to the terminal 1. The common wire is connected to the terminal 2. The comparator DA2 (chip К554САЗ) included on the classical scheme of comparison of two input signals, one of which must have greater stability. The input of the comparator is connected to terminal 3 of sensor GS1.

Operational amplifier DA1 with the elements VD1, R6, C2, R7, R9 provide a delay of 1 — 1.5 min required to eliminate false positives of the device when power is applied.

Diode VD1 prevents the leakage current of the oxide of the capacitor C2. Without this delay for 1 — 1.5 min after powering up, the device may include the audio signal regardless of the presence of alcohol vapors.

The output signal of the sensor GS1 is removed from the control point A. When the voltage under the influence of alcohol vapors with a concentration equal to or exceeding the limit at point A exceeds the set of RS elements the value of the input voltage U0 may vary in the range of 2.5 — 3.2 V At ambient temperature of +40°C and relative humidity of 65% and, respectively, in the range of 1.9 — 3.1 at a temperature of -10°C.

Without temperature balance diagram frequency response graph could vary in the range of 600 to 340 ppm for a given value of gas concentration of 1,500 ppm (at ambient temperature of 20°C and 65% humidity). For temperature compensation a thermistor is R1.

The results of applying the temperature balance of the resistor presented in the table.

The most significant aspects are the concentration of the gas expressed in million proportion (ppm), for example, the value of the gas concentration of 20 ppm means the concentration of alcohol vapors 20×10 (-6 degrees).

For details and installation

R1 thermistor — NTC, MMT or similar. The transistor VT1 replace КТ601, КТ603, КТ940 with any alphabetic index. The chip DA1 КР140УД12 replace КР140УД1208, КР140УД6.

The diode VD1 — KD521, KD522 with any alphabetic index. Oxide capacitors C1, C2 of the type K50-29 or similar. C1 smooths out the ripple voltage (important when the device is powered from the mains supply).

Sound emitter NA1 — any with a built-in generator 34 to the voltage 5 — 12 V.

Features practical application of the devices with a sensor of alcohol vapors

For a visual light alarm (optional for sound) parallel to the capsule HA1 (with built-in AF generator) is connected a led with series-connected resistor. The resistance of resistor 470 and 750 Ohms. Led type АЛ307БМ or similar with a current up to 10 mA are connected in accordance with the polarity — anode to the positive pole of the power source.

Electrical diagram of the control of alcohol vapors in the air

Electric diagram of the device control the alcohol vapors in the air

Power supply device — stable with a voltage of 5 V and a tolerance of ±5%.

Current consumption less than 70 mA (without led indicator).

Instead of sensor TGS 2620 in this scheme can be applied sensors TGS 880, NGS-2181 Murata company or, for example, the sensor TGS-822 (the latter requires a voltage supply of 12 — 15).

As one alternative, may be considered as an electronic comparator popular and inexpensive microprocessors, such as the company AMTEL, AVR. With appropriate programming this type of microprocessor is able to perform calibration and to take into account, for example, a function of temperature.

A. KASHKAROV, St. Petersburg

From the editor

Like any measuring device, the “breathalyzer” must undergo testing and periodic calibration in labs with appropriate licenses. Otherwise, the right will be considered the readings of the traffic police and the medical findings.

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