LOW COST ECG MACHINE DESIGN USING 8-BIT MICROCONTROLLER

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1 LOW COST ECG MACHINE DESIGN USING 8-BIT MICROCONTROLLER 1 Vinod J. Kadam, 2 Sanjay U. Waikar 1 Assistant Professor, Department of Information Technology, 2 System Analyst, Department of Computer Engineering, Dr.Babasaheb Ambedkar Technological University, Lonere, Tal-Mangaon, Dist-Raigad (Maharashtra) vjkadam@dbatu.ac.in, 2 suwaikar@dbatu.ac.in Abstract Electrocardiogram (ECG) is considered to be the backbone of cardiology. In this we have explored a suitable way of designing an ECG machine using 8-bit microcontroller and certain discrete components. Proposed system consists of AD624 as instrumentation amplifier to amplify the bio potential received from body using electrodes. This signal is then passed through analog filters to filter out unwanted signal like baseline wander, power line noises etc. Microcontroller is used to process data digitally to send towards LCD screen to display or data logging unit to provide storage of ECG for future usage. Finally we explored a way to transfer data over GSM Model to the physician. Keywords: Instrumentation Amplifier, Electrocardiogram (ECG/EKG), Microcontroller, R-R interval. 1. INTRODUCTION Electrocardiogram (ECG) is considered to be the backbone of cardiology. Now a day 1 12 channel ECG machines are available in the market which either directly provides the printed ECG graphs or shows the real time signal on LCD screen. But cost of such machines is very high that such machine is unaffordable for a common physician as well as for people who requires daily check up of ECG and derived parameters like R R interval, HRV etc. The typical ECG machine consists of Electrodes which works as transducer to receive the bio potential generated due to the electrical activity of the heart. This signal is then amplified by instrumentation amplifier to amplify it to desired level so that it can be fully justified by processor (in this case an 8 bit Microcontroller). This amplified signal is then passed through set of filters to filter out the unwanted signals. Now amplified signal is subjected to the digital processor through proper A/D converter. Here Microcontroller can be interfaced to numerous peripherals to provide

2 suitable user interface. In our system we are using LCD display, Logging device like MMC card or Flash drive, GSM model.[1][2] 2. PROPOSED SYSTEM Proposed system consists of Analog section which amplifies the signals to make it compatible with the digital processor. We are using ATmega32 microcontroller as a digital processor. Its unique feature is that it has an inbuilt A/D converter, 16Kbytes of flash, 2Kbytes of SRAM, 1Kbyte of EEPROM, supports various serial communications protocols like UART, SPI etc. Using SPI serial communication protocol, we can interface MMC card to the system for logging and storing the ECG signal for future use. The UART serial communication can be used to connect GSM module (Drone cells) to microcontroller to transmit the ECG data to the physician over GSM cellular network. The block diagram of the proposed system is shown in the next figure. Instrumentation Amplifier using INA122 or AD624 Analog Filtering ECG Electrodes 128 x 64 Graphical LCD display Mega32 as analog to digital converter and serial transmitter Send ECG file to physician over cellular Network MMC card for storage of ECG data 2.1 Analog Section Instrumentation amplifier Fig.1: Block diagram of the ECG Machine The INA122 [1] is a precision instrumentation amplifier for accurate, low noise differential signal acquisition. Its two-op-amp design provides excellent performance

3 with very low quiescent current, and is ideal for portable instrumentation and data acquisition systems. Fig.2: ECG Instrumentation Amlifier Courtesy: /ECG%20Report/E6001%20ECG%20final%20report.htm The INA122 can be operated with single power supplies from 2.2V to 36V and quiescent current is a mere 60uA. It can also be operated from dual supplies. By utilizing an input level-shift network, input common-mode range extends to 0.1V below negative rail (single supply ground). A single external resistor sets gain from 5 to Laser trimming provides very low offset voltage (250uV max), offset voltage drift (3uV/uC max) and excellent common-mode rejection Analog Filtering Using discrete components we have implemented one band pass filter to remove unwanted high frequency component, which can act as anti-aliasing filter.

4 2.2 Digital Section Fig:3 Analog filtering to remove unwanted noise In this section we are processing data in digital domain using 8-bit microcontroller (here ATmega32). Amplified signal is interfaced with ATmega32 using PORTA.1. Best feature of ATmega32 is that it contains in built ADC with 10 bit resolution [2]. The ADC of the mega32 samples the ECG signal at 512 samples per seconds. This is calculated using Nyquist criterion Graphical LCD interfacing We are using 128x64 graphic LCD to show the real-time ECG data. We first calibrate the LCD using grid similar to Oscilloscope, so that user can easily calculate the heart rate. Also we use some space on LCD display for user interface with the system to set the logging mode, to stop the data acquisition etc MMC Card We are using MMC card in SPI mode for data logging because ATmega32 supports SPI communication protocol The SPI mode consists of a secondary communication protocol that is offered by Flash-based SD Memory Cards. This mode is a subset of the SD Memory Card protocol, designed to communicate with a SPI channel, commonly found in Motorola's (and lately a few other vendors') microcontrollers. The interface is

5 selected during the first reset command after power up (CMD0) and cannot be changed once the part is powered on. The SPI standard defines the physical link only, and not the complete data transfer protocol. The SD Memory Card SPI implementation uses a subset of the SD Memory Card protocol and command set. The advantage of the SPI mode is the capability of using an off-the-shelf host, hence reducing the design-in effort to minimum. The disadvantage is the loss of performance of the SPI mode versus SD mode (e.g. Single data line and hardware CS signal per card). The commands and functions in SD mode defined after the Version 2.00 are not supported in SPI mode. The card may respond to the commands and functions even if the card is in SPI mode but host should not use them in SPI mode GSM Module We are using GSM modem for data transfer over cellular network. GSM is a GSM cellular modem for serial data rates of up to 115.2K bps. Compact size and quick installation provides an efficient replacement to serial cable for long distances where cellular service is available. Stand-alone modems provide efficient and low cost wireless communication for serial devices, loggers, data acquisition, and control systems. A simple setup includes a GSM modem with cellular account at the remote site/ logger and 56K dial-up phone modem at the base station connected to PC-software. For mobilemobile applications 56K phone modem can be replaced with GSM modem. GSM modems with cellular service allow for real-time monitoring and control of remote data loggers and irrigation systems by simply dialing into cellular or land phone networks. GSM modems are programmable using windows standard Hyper-terminal, AT commands. Each GSM modem requires a SIM card, cellular phone number and wireless Circuit-switched data (CSD) service from wireless service provider

6 3. CONSLUSION & FUTURE WORK We are working on the compression of ECG signal [3] and transmission of data over wireless network for telemedicine purpose. Also we are researching on data logging using USB flash drive as flash drives are common in the market. Sample prices of ECG Machines available in the market Machine Specification Price ECG-6012 (Twelve channel) US $ / Set Rs /- ECG-1206: Rs /- US $ / Unit 6 Channel ECG Machine 3-channels ECG machine US $ / Unit Rs /- Approximated cost Component Price Microcontroller ATmega32 Rs. 100/- Graphic LCD Rs. 600/- MMC card with Adapter Rs. 400/- GSM Module (Optional) Rs. 5000/- Other Discrete Component Rs.500/- Grand Total Rs.6600/- (with GSM Module) Rs. 1100/- (without GSM Module) 4. REFERENCES 1. Electrical Activity of heart available at: 2. SD Specifications Part A1 Advanced Security SD Extension Simplified Specification Version 2.00 May 18, 2010

7 3. Nikam, V. B.,Vinod kadam, BB Meshram Image Compression Using Partitioning Around Medoids Clustering Algorithm IJCSI International Journal of Computer Science Issues, Vol. 8, Issue 6, No 1, November 2011." ISSN