Low Cost Solar ECG with Bluetooth transmitter

Parin Dedhia Harsh Doshi Mrunal Rane Govinda Ahuja Biomedical Engineering Biomedical Engineering Biomedical Engineering Electronics Engineering D.J.Sanghvi c.o.e. D.J.Sanghvi c.o.e. D.J.Sanghvi c.o.e. NMIMS University Mumbai, India Mumbai, India Mumbai, India Mumbai, India parin99@hotmail.com rockinharsh90@yahoo.com mrunalrr@gmail.com govindaahuja@gmail.com Abstract- Cardiovascular disease is the world's leading killer, accounting for 16.7 million or 29.2 per cent of total global deaths every year. The World Health Organization estimates that 60 per cent of the world's cardiac patients will be Indian by 2010. The reported prevalence of coronary heart disease (CHD) in adult surveys has risen 4-fold over the last 40 years and even in rural areas the prevalence has doubled over the past 30 years. The Electrocardiograph (ECG) is a diagnostic instrument which measures the electrical activity of the heart, providing valuable information of cardiac disorders like infarction, Atherosclerosis, etc. ECG instruments used in hospitals are bulky, work on line voltage which makes the ECG waveform distorted and an isolation amplifier is needed for patient’s safety making it expensive thus cannot be used in underdeveloped areas. We have developed an inexpensive portable solar powered ECG. 63% of all rural households in India do not have electricity and use fuel for lighting. Thus, being solar powered will eliminate its dependence on electricity and can easily be used in areas either with no electricity or with lots of load shedding. The electro-cardiogram will be free from the line frequency noise. Advantage of this equipment is the backup option of charging the batteries using a simple mobile charger. The device is capable of acquiring up to 34 hours of continuous electrocardiogram data at a sample rate of 500 Hz. The ECG is also transmitted to the patient’s cell phone or a computer with the help of a Bluetooth transmitter.

Keywords- portable; solar; line frequency noise; sample rate

I. INTRODUCTION

The cardiovascular crisis is glaringly evident in developing countries. Both the urban and rural areas are experiencing a mounting epidemic of cardiovascular (CV) disease, which was until recently considered a disease of the 'urban rich' [1]. The most important reason for this epidemic is related to the economic and cultural influences of globalization [2]. ECG machines are best to diagnose CV diseases and they require high power to run the motor of thermal printer. Electricity losses in India during transmission and distribution are extremely high and vary between 30 to 45% [3]. Due to shortage of electricity, power cuts are common in developing countries of the world which has adversely affected their economic growth. For example, despite an

ambitious rural electrification program, around 400 million Indians still have no access to electricity [3].

Looking at both these fundamental issues with alarming statistics, it is essential to develop equipment which can monitor cardiac activity, with minimum dependency on line voltage and is low cost to aid the rural sectors.

II. SYSTEM DESCRIPTION

Our aim was to design an inexpensive electrocardiograph powered by solar cells, yet acquiring an excellent quality signal which every clinician strives to secure every time they monitor a patient’s heart.

A. Hardware Description Figure 1 shows the block diagram of the device.

i. Solar power

6V/3W solar panel powers the rechargeable battery (LSD-NiMH), which in turn powers the equipment. Random frequencies superimpose the DC output from the solar panel, thus can reduce the charging-discharging cycles of the battery. De-coupling capacitors are hence used to ground the high frequency noise. The output voltage of the solar panel needs to be regulated to 6.5V in order to safely charge the batteries. Reverse charge protection circuit is used to avoid discharge of

Figure 1. Patient acquisition and processing module

2012 International Conference on Biomedical Engineering (ICoBE),Penang,Malaysia,27-28 February 2012

978-4577-1991-2/12/$26.00 ©2011 IEEE 419

batteries through solar panels in low lightNiMH batteries deliver 5V DC to power the Calculating charge time required: For a fully discharged LSD-NiMH battery, charge time can be calculated using the follo

Battery Type Self-Discharge Rate Chara

Lithium-ion (Li)

Does not hold charge well over long periods. Loses 8 percent per month, much more in warm temperatures [4], [5].

Workthat rampersuch aNo meHighlin con

Low-Self Discharge Nickel-Metal Hydride (LSD NiMH)

Holds charge well over long periods. Loses 15 percent per year, very slightly more in warm temperatures [4], [5].

Workthat rampersuch aNo meEco-fr

Nickel-Cadmium (NiCd)

Loses 1 percent per day, slightly more in warm temperatures [4], [5].

Does devicesuddedischaSuffereffectEnvirohazard

Lead-acid Loses 8-15% charge per month [4], [5].

Low c(sealeLimiteperforVentemaintCells heavy

After consistent research and laboratorthe above batteries, we concluded the forepresentation.

Table 1 Comparison of Different Rechargeable

t conditions. LSD-e main circuit.

an approximate owing formula [4]:

120%

acteristics

s well in devices equire sudden high rage discharge, as digital cameras. emory effect. y explosive when

ntact with water.

s well in devices equire sudden high rage discharge, as digital cameras. emory effect &

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Figure 2 show that LSD-Ndischarge rate thus ideal for ou

ii. Sensors

Four clamp electrodes arebeing reusable and inexpendeveloped areas where a frelectrodes is practically imprepresents all the three Einthovconvention, lead I have the po(LA), and the negative electrotherefore measure the potentiarms.

iii. Bio-amplifier & D Biological signals such measure around several micro-signal recorded by sensor hasTherefore an instrumentation very high input impedance of 1

e Batteries

Figure 3. Eintho

Figure 2. Performanc

NiMH batteries have low self-ur device.

used in our design. Electrodes nsive can be used in under equent delivery of disposable possible. The acquired signal ven bipolar leads (Figure 3). By ositive electrode on the left arm ode on the right arm (RA), and ial difference between the two

Driven Right Leg Circuit

as ECG (Electrocardiogram) -volts (millionths of a volt). The values in the range 1 to 3mV. amplifier with a gain of 1000,

10GΩ and a CMRR greater

oven Triangle [6]

e evaluation of various batteries

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than 110 dB is required. Instrumentation amplifier used also consumes very less power making the device energy efficient. Unfortunately, the patient's body can also act as an antenna which picks up electromagnetic interference, especially the line frequency noise. This interference can obscure the biological signals, making them very hard to measure. A Driven Right Leg Circuit or “DRL” circuit is an electric circuit that is often added to biological signal amplifiers to reduce Common-mode interference. Right Leg Driver circuitry is used to eliminate interference noise by actively canceling the interference.

iv. Signal Conditioning

Acquisition of quality ECG data is critical in providing accurate and timely diagnosis and patient treatment. Poor ECG quality can result in: • The monitor’s inability to recognize the R-wave, thus

affecting arrhythmia analysis and the ability to perform procedures such as synchronized cardio version and transcutaneous pacing,

• False alarms and unnecessary troubleshooting, potentially delaying treatment.

Thus it is important to have a very efficient signal conditioning circuit.

Figure 4 shows the frequency response of different active filters. The Butterworth filter rolls off more slowly around the cutoff frequency than the Chebyshev filter or the Elliptic filter. The Butterworth filter has ripple free frequency response, giving it a flat pass band and making it ideal for medical applications.

Figure 5 shows PSPICE simulation of the frequency response of second order Butterworth band pass filter and a notch filter (50Hz). With the help of PSPICE simulations and experiments, we conclude that Second order Butterworth filter is ideal for our application.

v. Signal Digitizing

The output of the ECG is in analog form. In order to transmit it as well as get it displayed on a graphics LCD, the analog signal needs to be converted into digital signal using an A to D convertor. A PIC microcontroller is used for analog to digital conversion. This device is low cost 8-bit CMOS Flash Microcontroller based on RISC technology with 10-bit multi-channel Analog to Digital converter. According to the Nyquist criterion, the sampling frequency should be twice greater than the signal frequency. Thus, 500Hz sample frequency is selected with an 8 bit resolution, as provided by the microcontroller. Instead a 12-bit microcontroller can be used to fulfill the requirements of telemetric emergency services.

vi. Bluetooth wireless transmission

Figure 4.Comparison of Classical IIR Filter Types [7]

Figure 6.BISM II Bluetooth module from Ezurio [8]

Figure 5 .Response of designed active filters used in the ECG acquisition

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Bluetooth being the easiest and quickest mode of wireless communication these days has been chosen in our design over conventional thermal printer. Thermal printers are not energy efficient thus consuming high amount of power in driving its motors. Thermal printing isn’t highly reliable as the print fades off over a period of time. Avoiding the use of papers as well as being a solar powered makes the device complete eco-friendly. Digital data transmitted via Bluetooth can be preserved by the patient in his cell phone or computer over a long period of time.

Thus the equipment requires Bluetooth to transmit data to the computer or cell phone and then over the internet to any doctor. The Bluetooth module used was the BISM II chip from EZURIO (Figure 6). Both the microcontroller and the Bluetooth chip are involved in the process of transmitting data wirelessly. Packets that contain signal information are sent to the chip, using their USART module as interface. Any device connected via Bluetooth to the circuit board can thus receive them in real-time.

vii. Display on Graphic LCD The three leads ECG waveform is displayed on the 128x64 dots GLCD. The graphical LCD display is a memory mapped peripheral that permits menu-driven user interaction, warning messages, and real-time signal display [9]. The display that we used (LCD-128G064E) has a 128 x 64 dot matrix in a 54 mm x 50 mm module [10]. The LCD controller and LED back light required 5V for operation. The display draws 5 mA when it is on [10]. LCD-128G064E is inexpensive and consumes low power making it ideal for this system. Its compactness allows in designing a very portable device.

viii. Energy efficiency and power consumption

The device aimed to transform the healthcare in under developed areas needs to be very low on power consumption, in turn highly energy efficient. Backlight LCD consumes good amount of power in any device. LCD-128G064E consumes 49.5mA of current with maximum brightness [10]. Current consumption can easily be brought down by controlling the brightness using a potentiometer. Instrumentation amplifier is highly energy efficient consuming only 1.3mA of current. Operational amplifiers used in the hardware consume not more than 1mA of current. PIC microcontroller consumes extremely less current in order of micro amperes and the Bluetooth module consumes about 20mA of current [8]. Considering total current consumption of 70mA and charge capacity of LSD-NiMH batteries as 2400mA, a maximum resulting autonomy of 34 hours is achieved which can be increased with a potentiometer (controlling brightness) and higher charge capacity batteries.

ix. Development environment

The specification, design and implementation of the acquisition module were carried out using ORCAD®, Proteus Professional V7.6®. ORCAD software was used to create PSPICE simulations of frequency response of Butterworth filter and notch filter. Proteus Professional was used to design PCB layout for the hardware design.

III. RESULTS

Figure 7. Distorted ECG waveform with line frequency noise

Figure 7 shows an ECG waveform distorted by line frequency noise (50Hz). Figure 8 shows an undistorted noise-free ECG waveform which can be used for detection of cardio-vascular diseases. The line frequency noise superimposed on the ECG signal degrades the quality of the signal, wherein the P, Q, R, S and T wave cannot be examined effectively (Fig. 7). Use of effective analog filters and

Figure 8. Noise-free and undistorted ECG wave form

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elimination of mains power supply helped in achieving high quality ECG. The above results will further be improved after an effective insulating fabrication of the device. The displayed output is an Amplitude v/s Time ECG waveform.

IV. CONCLUSIONS

On comparing figure 7 and 8, it can easily be concluded that a noise-free and undistorted ECG can be achieved with the use of batteries, a notch filter and a right leg driven circuit. The quality of the ECG waveform is not compromised by making the device inexpensive and solar powered. Conducting clinical trials on 10 cardiac patients by the cardio surgeon, it was proved that this device is efficient in arrhythmia detection. The device is designed using inexpensive components viz. (Batteries, Solar cells, ECG electrodes, ICs and GLCD) without affecting the quality of the ECG. The project was designed and implemented in $50, making it highly inexpensive and ideal for under developed and developing nations.

ACKNOWLEDGMENT We would like to acknowledge cardio surgeon Dr. Akshay Kumar for conducting patient trials for our device. We would also acknowledge Saloni vora and Aashumi vora for helping us out with the graphics.

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professionals, Jan. 16-31, 2009. [2] S. Mayor, “Cardiovascular disease threatens developing countries,”

BMJ 2004; 328: 1032 DOI: 10.1136/bmj.328.7447.1032-b, April 29, 2004.

[3] India Core, Information on Indian Infrastructure & Core Sectors, Aug.26, 2010.

[4] National Institute of Justice, New technology batteries guide, NIJ guide 200-98.

[5] Woodbank Communications Ltd. [Online]. Available: http:// www.mpoweruk.com/performance.htm.

[6] E. Levine (2010, August). Electrocardiography [Online]. Available: http://emedicine.medscape.com/article/1894014-overview.

[7] C. Sidney Burrus (2008, November), “Design of Infinite Impulse Response (IIR) Filters by Frequency Transformations,” [Online]. Available: http://cnx.org/content/m16909/latest/.

[8] Ezurio, “Bluetooth® Serial Module BISM II”, USA [Online]. Available: www.iec.dk.

[9] J. Segura-Juárez, D. Cuesta-Frau*, L. Samblas-Pena, and M. Aboy, “A Microcontroller-Based Portable Electrocardiograph Recorder,” IEEE Transactions on Biomedical Engineering, VOL. 51, NO. 9, September 2004.

[10] Vishay, “LCD-128G064E data sheet,” Europe.

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