GOVERNMENT ENGINEERING COLLEGE WAYANAD

PORTABLE SYSTEM FOR PHYSIOLOGICAL SIGNAL

MONITORING AND RECORDINGECG data acquisition and recording

A Brief Report

I. BLOCK DIAGRAM

Block diagram

BLOCK DIAGRAM EXPLANATION

1. LEADS:

The word lead may be used to refer to the electrical cable attaching the electrodes to the ECG recorder. The word lead may also refer to the tracing of the voltage difference between two of the electrodes and is what is actually produced by the ECG recorder.

2. AMPLIFIER:

It consists of an instrumentation amplifier (AD620). The output of the sensor is given to the input of the amplifier. The AD620 is a low cost, high accuracy instrumentation amplifier that requires only one external resistor to set gains of 1 to 1000. Alternate instrumentation amplifiers like AD624 are also possible.

3. FILTER

A low pass filter is incorporated in this stage to avoid the high frequency region of the amplified signal. The signals are filtered using LM358 OP-amp. It is to avoid the noise of the signals. It has two internally compensated op amps and eliminates need for dual supplies. Allows direct sensing near GND and VOUT also goes to GND. It is compatible with all forms of logic and power drain suitable for battery operation. The analog input charges a sample and hold capacitor. The output of the sample and hold capacitor is the input into the converter.

4. MICROCONTROLLER

For meeting our project requirements we are using PIC16F877A as the microcontroller. This section has the portions of A/D conversion, LCD interfacing, MMC interfacing, USART communication part. One of the most popular and easy to use microcontroller families available in the market today is the Microchip “PIC microcontroller.” Originally known as the PIC (for Peripheral Interface Controller), the PIC microcontroller MCU consists of over 400 variations (or Part Numbers), each designed to be optimal in different applications. These variations consist of a number of memory configurations, different I/O pin arrangements, amount of support hardware required, packaging, and available peripheral functions. This wide range of device options is not unique to the PIC microcontroller; many other microcontrollers can boast a similar menu of part numbers with different options for the designer.

5. MMC

The MMC card and the SD card are flash memory storage based devices, and are physically very similar. Both card types support proprietary data transfer protocols using four data bits, and are compatible though having different initialization. The major difference is that the SD card is designed to provide optional security by allowing encryption of the device contents. The MMC card supports additional bus widths (up to 8 bits). The SD card also supports several modes that are not present in the MMC card, including SDIO (secure digital input/output) that can be used as an external communications interface using the standard SD card format. Both card types also support a basic SPI type interface for simple connection to embedded devices. The SD card specifications state a maximum clock frequency of 25MHz, and the MMC specifications state a maximum clock frequency of 52MHz depending on the device. Figure shows the MMC/SD card connections when configured for SPI mode operation.

6. INTERFACE Here interface refers to the communication with the software installed in

PC. The communication is done using the IC MAX232 which act as a level converter. It works as a buffer between the TTL logic supported by the microcontroller and the RS232 standard used in PC.

7. COMPUTER Computer is the final device required for the completion of the project. A Visual

basic program is installed in the computer which is intended to view the recorded data as real time as well as recorded format.

CIRCUIT DIAGRAM

Amplifier section

Microcontroller section

PC Interface section

MMC Interfacing

WORKING

We developed a small stand alone device that can monitor the ECG of a patient

and store the data in Multimedia Card attached to it up to 1 month continuously. This

system can be used to record the ECG data of the patients at home or any other place.

This data can be verified at the hospital or by the doctor at his home PC.

Lead1 and lead 2 are ECG sensors. This output varies upon the pulse variation.

The output of the sensor is analog voltage. It consists of an instrumentation amplifier

(AD620). The output of the sensor is given to the input of the amplifier. The AD620 is a

low cost, high accuracy instrumentation amplifier that requires only one external resistor

to set gains of 1 to 1000. Furthermore, the AD620 features 8-lead SOIC and DIP

packaging that is smaller than discrete designs, and offers lower power (only 1.3 mA

max supply current), making it a good fit for battery powered, portable (or remote)

applications. The AD620, with its high accuracy of 40 ppm maximum nonlinearity, low

offset voltage of 50 mV max and offset drift of 0.6 mV/°C max, is ideal for use in

precision data acquisition systems, such as weigh scales and transducer interfaces.

Furthermore, the low noise, low input bias current and low power of the AD620 make it

well suited for medical applications such as ECG and noninvasive blood pressure

monitors.

These signals are given to the filter to avoid the noise of the signals (LM358).

The LM358 consist of two independent, high gain, internally frequency compensated

operational amplifiers which were designed specifically to operate from a single power

supply over a wide range of voltage. Operation from split power supplies is also possible

and the low power supply current drain is independent of the magnitude of the power

supply voltage. Application areas include transducer amplifier, DC gain blocks and all

the conventional OP-AMP circuits which now can be easily implemented in single power

supply systems.

The output of the amplifier is analog signal. This analog signal is given to the ADC

channel of the input. The microcontroller consist a10 bit ADC, which converts the analog

voltage to corresponding digital values. These values are stored in its memories. The

analog input charges a sample and hold capacitor. The output of the sample and hold

capacitor is the input into the converter. The converter then generates a digital result of

this analog level via successive approximation. This A/D conversion, of the analog input

signal, results in a corresponding 10-bit digital number.

Calibrate these values and stores its in MMC card through SPI module of the pic

microcontroller. The Master Synchronous Serial Port (MSSP) module is a serial interface

useful for communicating with other peripheral or microcontroller devices. These

peripheral devices may be serial EEPROMs, shift registers, display drivers, A/D

converters, etc. The MSSP module can operate Serial Peripheral Interface (SPI).

The RS-MMC Cards are highly integrated flash memories with serial and random

access capability. It is accessible via a dedicated serial interface optimized for fast and

reliable data transmission. This interface allows several cards to be stacked by through

connecting their peripheral contacts. These RS-MMC Cards are fully compatible to a

new consumer standard, called the Multi Media Card system standard define in the Multi

Media Card System specification. The Multi Media Card system is a new mass-storage

system based on innovations in semiconductor technology. It has been developed to

provide an inexpensive, mechanically robust storage medium in card form for multimedia

consumer applications. RS-MMC Card allows the design of inexpensive players and

drivers without moving parts. A low power consumption and a wide supply voltage range

favors mobile, battery-powered application such as audio players, organizers, palmtops,

electronic books, encyclopedia and dictionaries. Using very effective data compression

schemes such as MPEG, the RS-MMC Card will deliver enough capacity for all kinds of

multimedia data.

The ECG data are stored in RS- MMC card up to more than ten days. If the device is

connected to the computer recorded data (stored in MMC) send to the computer through

USART module of the microcontroller. The Universal Synchronous Asynchronous

Receiver Transmitter (USART) module is one of the two serial I/O modules. (USART is

also known as a Serial Communications Interface or SCI). The USART can be

configured as a full duplex asynchronous system that can communicate with peripheral

devices such as CRT terminals and personal computers, or it can be configured as a

half duplex synchronous system that can communicate with peripheral devices such as

A/D or D/A integrated circuits, Serial EEPROMs etc. The computer receives these data

and plot an EGC graph using system level language such as visual basic or visual c++.

The microcontroller has CMOS standard. But computer has RS standard. So a interface

circuit is used (MAX 232 or HIN 232). The HIN232 or MAX 232 is RS-232

transmitters/receivers interface circuits meet all ElA RS-232E and V.28 specifications,

and are particularly suited for those applications where ±12V is not available. They

require a single +5V power supply and feature onboard charge pump voltage converters

which generate +10V and -10V supplies from the 5V supply.

MICROCONTROLLER SECTION The VCC is connected to 11th pin of pic. The

capacitor is used for to ground the AC content of the vcc.1st pin is reset pin. If a zero

potential across the 1st pin then the system is reset. So reset switch press, then the

voltage is grounded and system reset. 13 and 14 pins are used to clock of the pic. So a

crystal is connected to that pins. Two capacitors, one is used for oscillation start and

other is used for phase shifting, connected to that pins.

The output of the ECG is connected to the 2nd pin of the PIC (Channel 0 of ADC). The

USART pins are 25th (TX) and 26th (RX) of the PIC. These are connected to the serial

port. The SPI pins (pin number 18(clock), 19 (SPI out) and 20(SPI in)) are connected to

the MMC card.

Plotting of recorded

The software developed in visual basic is intended for plotting the real time as well as

the recorded data which is transmitted through serial port. The software is user friendly

and very easy to use. The screen shot is given below.

SOFTWARES USED

‘Embedded c’ is used for programming the microcontroller. MPLAB IDE is the software used for compiling the code and for generating the HEX file for loading

in to the IC. Proteus is the software used for simulating the designed circuit. Visual Basic application is also designed for plotting the real time ECG as well as the recorded

ECG. Tiny bid is the boot loader used.