Contents
Introduction1) The general formulation of the problem
3) Description of the specialized computer system
Living tissues are conductors of electricity. The different tissues have different electrical conductivity. Have the lowest resistance of liquid environment of the body, especially blood. If through some part of the body to pass harmless to the organism alternating electric current of high frequency (about 500 kHz) and low power (less than 10 mA) and simultaneously recording electrical resistance of this site, it appears that such resistance will be constantly changing connection with the passage of the pulse wave tissue. The more blood circulation in tissues, the lower their resistance. Thus, the curve of the change in resistance from well-reflects the blood circulation in tissues by passing them on the pulse wave. This makes it possible to judge the state of blood flow in certain areas of the body or organ (limbs, brain, heart, liver, lungs). To affect blood circulation in the tone charges and total amount of blood, so rheography gives an indirect idea of the peripheral resistance of stoichiometric flow of blood in the vessels and the amount of circulating blood. In medicine rheography used as part of diagnostic techniques for diseases of the heart and vessels and other internal organs, and blood loss and shock.
The general formulation of the problem
In conducting computer tests of verbal, designed to determine psihih-mechanical state of a person or his overall level of development, it is necessary to reveal the answers to questions that have a high validity. To that end, the test is administered a number of additional issues, which increases the total time of the test. The answers are not respective truth activate the sympathetic nervous system and causes physiological parameter changes: blood pressure, body temperature, pulse, respiration amplitude, the electrical activity of the skin, the flash frequency, changing the rhythm of the brain. Was detected for those changes, you can use lie detectors (polygraph). These devices are bulky and expensive, so their use in solving this problem netse-expedient.
To solve this problem, such a device was not used before in this publication on this subject no.
The purpose of this study is to develop a specialized computer system (SCS) measuring the temperature region of the human body in real time.
To achieve the goal should be to solve the following problem:
1) selection of temperature sensors;
2) selection of electronic components for the registration of the resistance section of those la Rights;
3) choice of method switching devices and PCs;
4) to implement the instrument.
Description of the specialized computer system
Specialized computer system is based on the principles of rheograph and thermography. Rheograph - a device for recording a relatively fast pulse oscillations of blood flow [1]. Thermography - a device for detecting thermal-field object.
Thermograph in the SCS uses the temperature sensors DS18B20 company "Dallas Semiconductor". Sensors can measure temperature with an accuracy of ± 0,5 ° C from -10 ° C to +85 ° C. Unique and immutable 64-bit serial number which is used as a sensor node address, you can connect to one bus set temperature sensors. On the market there are many different temperature sensors, deserves special attention is DS18B20, since it has high accuracy, a wide range of pa-bochy and low cost and simple way to implement the device. The human body is fixed by 3 temperature sensor with adhesive plaster (the thin fabric coated with a sticky mass). Rheography method is based on Ohm's law [2]:
where, I - current, flowing through the tissue, A;
V - voltage drop on the section between the electrodes, V;
R - resistance, ohms.
Resistance measurement is made using special electrodes zafik-pensate for the human body that allow design features of the device. Before the beginning of a computerized test of verbal, to a person connected sensors are devices that allow you to record physical parameters that are passed to a PC device.
To measure the resistance and temperature region of the human body developed the device, whose scheme is shown in Fig. 2.
Schematic diagram of the device was designed using the software package DipTrace, developer Novarm. DipTrace - computer-aided designing-tion (CAD) to design printed circuit boards (PCB). The package includes four programs: Schematic - schematic design; DipTrace - creating cards, manual and automatic-parameter trace; ComEdit - Editor buildings; SchemEdit - editor of the components. Pro-gram has the most comfortable, including CAD for PCB design, Paul zovatelskim interface. All work is accompanied illuminated editable and dependent on them that depend on the elements to visually assess the situation. The logical structure of the concept or the motherboard is formed immediately when building and changing one element affects depend on it [4].
The device is assembled on the microcontroller (specialized microcomputer) Atmega8-16AU (Figs. 2 and 3) the company «Atmel». This controller has an 8 Kbyte Flash mem-ory (internal non-volatile memory) for program code, as well as 512-bit Eeprom (internal volatile memory), calculated at 100,000 write cycles [5]. Mickrokontroller clocked external quartz crystal, 8 MHz.
IC Atmega8 a budget decision, and in addition the microcontroller has all the necessary ports for the implementation of the device.
Atmel Corporation - manufacturer of semiconductor electronic components. The company was founded in 1984. One of the leading manufacturers of microcontrollers (MCS-51, ARM, AVR, AVR32). It also develops and manufactures small modules pendent non-volatile memory for electronic devices, FPGAs, digital circuits, radio receivers and transmitters, fingerprint scanners. Company to its customers may propose to the system on a chip that combines the requested components.
Atmel products are widely used in computer networks, industry, medicine, communications, automotive, space, military units, as well as credit cards [6].
By means of serial peripheral interface (SPI) controller is obtained from an external analog-digital converter (ADC) - ADS1256 (Fig. 2, 4), the company «Texas Instruments». This analog-digital converter is 24 bits-nym, low-noise device, with a maximum frequency of 30,000 samples per second [7], ie, one second we can get up to 30000 measurements. ADC has an external quartz resonator at 8 MHz and a voltage reference REF192 -2,5 V (Fig. 2, 5).
Analog-digital converter - ADS1256 most expensive element in the whole have designed, but it has the lowest price among the devices in its class.
Texas Instruments (NYSE: TXN) - U.S. company, a manufacturer of semiconductor components, circuits, electronics, and products based on them. Located in Dallas, Texas (USA).
Is the world's fourth-sized manufacturer of semiconductor devices, second only to Intel, Samsung and Toshiba. Ranked first in the production of micro-circuits for mobile devices, as well as first place for the production of digital signal processors (DSP) and analog semiconductors. The company also produces ICs, we have for broadband modems, computer peripherals, consumer electronic devices-properties and the RFID-tag [8].
Switching device with your computer using a universal successive Bus (USB) (Fig. 2, 1). Transferring data from microcontroller to computer-implemented the FT232BM company «FTDI» (Fig. 2, 2). Such apparatus converse solution makes it easy to implement a device that uses a connection to computer, USB. Maximum data transfer rate for trans-Chairman FT232BM is 1 Mbit / s [9].
Converter FT232BM used because is the most widespread dissemination of in its class, this explains its low cost compared to competitors. To use this chip should be the minimum number of additional electronic components.
FTDI (Future Technology Devices International) - Scottish private company, the torus-guyuschaya semiconductor devices. Specializes in the field related to the Shea-term USB. It develops, manufactures and supports equipment and respective software drivers to convert the serial data via RS-232 or TTL level signals in the bus USB, in ord er to enable the modern nym computers to use the old devices.
FTDI also provides consulting services for the design of specialized integrated circuits. The main product the company is FTDI Chip, integrated circuit, the widely used in electronic devices that use microcontrollers, such as the Arduino platform for physical computing [10].
The maximum possible number of data packets (N, 1/s), transmitted by the computer (PC) per second depending on the length of one packet of data (Lp, bit) and data transfer rate over a communication channel (Vch, bit / s) calculated by the formula:
Bit temperature sensor DS18B20 installed software and can be 9 - 12 bits, so the maximum number of data packets consideration, on a personal computer may be different.
Table 1. Limit the number of data packets transmitted per second on a PC, depending on the number and capacity of DS18B20 (A / D converter - 24 bit)
As can be seen from the table, despite an increase in the number of temperature sensors can monitor readings with great frequency.
To obtain rheogram enough to register the value of resistance with the interval of 2 ms. Full rheographic cycle is equal to the duration of one cardiac cycle 0,3 - 1,5 s [3].
where, N - number of registration of physical indicators;
HR - heart rate;
r - interval measurements, мс;
According to this formula to calculate the number of registration statements (N, 1/s), for heart rate (HR) in the range of 40-205, and the interval (r, ms) to equal 2. Obtain.
Application of electronic components provide the required frequency of fixations of physical parameters. Specialized computer system has great potential for scaling the number of sensors, while expanding the problem
Appearance is shown in Fig. 3 and 4. The device is implemented on a single-sided PCB, with the physical dimensions of the device without housing are 81.5 x 36.5 x 15 mm and weighs less than 25 g. Such dimensions of the device were obtained by the use of electronic components in the housings SMT.
Connectors for the electrodes (1), microcontroller programming (2), temperature sensors (3), the USB (5) and temperature sensors DS18B20 (4).
With a cable USB, the device connects to the PC. Three-pin connector raster-wavelength (Fig. 3, 3), performs switching of the temperature sensors and devices. For four of the discharge pin plug (Fig. 3, 1) connect the electrodes, and the seven discharge (Fig. 3, 2) - Connector programmer to debug the operation of the microcontroller.
The FT232BM (1); microcontroller Atmega8-16AU (2) ADC ADS1256 (3), a voltage reference Ref192 (4); connector cable USB (5).
Developed a specialized computer system that registers the temperature and the resistance area of the human body in real time. The system consists of temperature sensors and electrodes attached to the body of the test, the registration of the device resistance and temperature as well as the computer that are trans-biometrics. Used schematic solutions enable us to obtain data-operate with high accuracy and speed.
The advantages rheography include non-invasive, the ability to con-dit study virtually unlimited number of vascular areas, for a long time and in any conditions, weak, painless and harmless for the patient, ease of conducting studies of the, information, speed data acquisition - the lack of a long cycle of measurement . In most cases, using surface electrodes for each of the studied zones requires two rheographic electrode, the location of which depends on study pools of blood circulation. For example, in studies of blood flow to the extremities, (hands and feet) using special metal tape measure or rectangular metal plates. To study the cerebral blood flow using circular electrode with a diameter of about 20 mm. Rheogram characterizes the state of the vessels in the area between the electrodes. Using rheography with thermography can significantly reduce the time tit-verbal test, but also increases the reliability of the results.
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