SmartECG: An affordable solution for screeningcardio-health issues

Amit Kumar MishraElectrical Engineering Department

University of Cape Town, South AfricaEmail:akmishra@ieee.org

Paul Thomas RichardsElectrical Engineering Department

University of Cape Town, South AfricaEmail:paulrchds@gmail.com

Abstract—Major studies have reported that heart related issueswill be a major health risk in developing and developed countriesalike. The problem is more acute in developing nations because ofthe lack of enough trained cardiologists and also because of thehigh cost of the traditional electro cardio grams (ECGs). In thecurrent work we propose a design for a low-cost and user firendlysmartphone based ECG (SmartECG). The major contributionsof the work lie in the innovative design of the analog part andin the efficient use of the limited processing power of a smartphone to display and store the ECG, and extract some of themajor features from it.

I. INTRODUCTION

Because of poorer lifestyles, heart related diseases areexpected to be a major cause of disability of working agepopulation in the coming decade. This demands for a low-costportable heart monitoring system which can do the preliminaryanalysis of a person’s cardiac health in a semi-autonomousfashion. Such a system would be expected to help (and notreplace) the cardiologists. Because of this, portable electrocardiograms (ECG) has been a major area of research recently.

The research in the field of portable ECG can be divided intotwo major groups. One set of work are more concerned withdeveloping a portable integrated medical diagnostic kit [1],[2]. The second group tries to develop smaller and ubiquitousECG monitoring specially with the use of wireless sensors[3], [4]. In these systems the major demerit is the fact thatthese systems try to achieve a high level of sophistication andthereby increasing the cost. Hence these are not solutions fordeveloping and underdeveloped countries.

In the current work we propose a smart-phone based ECG(SmartECG). There are two major novelties. First of all we tryto move as much signal processing as possible to the digitaldomain. And hence we use the smartphone’s sound-card’sADC for sampling the signal. This design comes from oneof our earlier patents []. This causes many challenges and themajor one is the poor response of the integrated ADC in lowfrequency. This is covered in our next contribution in whichwe use a simple low-cost modulation circuit to modulate theECG signal to a higher frequency. The overall design is low-cost and works seamlessly with an Android phone. We havealso developed the required application (which include all thedigital signal processing required) for the SmartECG.

Rest of the paper is organized as follows. Section II dis-cusses the existing low-cost ECG systems in open market.

Section III details the proposed design. Section IV shows someof the results and the paper is concluded in Section V.

II. SURVEY OF EXISTING LOW-COST ECG MONITORINGSYSTEMS

There are quite a few portable ECGs available in the openmarket. We summarize the features of some of the major onesin Table 1. Two important things to note from the table areas follows. First of all even the cheapest system is muchcostlier than what a developing nation’s citizen can afford.Secondly, the only system which supports Android phonebased monitoring is very costly. It should also be mentionedhere that because of the open-source nature of Android OS,there is a surge of inexpensive smart phones in the developingnations. Hence, it can safely be assumed that within a fewyears almost everyone will have an access (if not ownership)to Android based smart-phones.

III. DESIGN OF THE SMARTECG

In this section we detail the design of the SmartECG systemthat we have developed. There are two major developments inthis work, viz. 1) the analog front-end, and 2) the digital dataacquisition, processing and display.

A. Analog front-end

One of the major innovations in our design is the fact thatwe do not use any analog to digital converter (ADC) in theanalog front-end circuitry. This makes the design simple andhence inexpensive. As an alternative we use the ADC whichis a part of the embedded sound-card of the smart phone.To access this we feed in the signal using the microphonepin of the phone. The major challenge in this is that ADCsof smart-phones are highly optimized to work for the audiofrequency. Figure 1 shows the frequency response of a typicalsmart phone. And Figure 2 shows the frequency response ofa measured ECG signal. We can mark that the ECG is a lowfrequency signal and the smart-phone ADC does not supportthe frequency contents of ECG.

To take care of the above problem, we used a frequencymultiplier in the front-end to upconvert the ECG signal toa higher frequency band. In our design we upconvert it by1kHz which we generate using an inexpensive Wein-bridgeoscillator.

Figure 3 gives the detailed circuit diagram for the analogfront end. We describe different parts of the circuit below.

• The sub-circuit shown in red generates a buffered virtualground.

• The sub-circuit shown in green is the Wein-bridge oscil-lator which is responsible for generating the sinusoidalcarrier signal for modulation.

• The sub-circuit shown in blue is the instrumentationamplifier which is connected to the right leg driver circuit.

• In the sub-circuit shown in yellow the signal goes throughan active band-pass filter. The op-amp in this filter alsoprovides a gain to the signal.

• The sub-circuit shown in brown is the multiplier IC whichmultiplies the modulating signal with the carrier signal.

Fig. 1. A typical Android phone’s ADC frequency response

Fig. 2. Frequency response of measured ECG signal

B. Digital signal handling

The up-converted signal is fed into the smart-phone throughthe microphone connection. The sound card’s ADC is operatedat a rate of 8000 samples/s. The binary data stream is retrievedfrom the sound-card and converted into an array of integers.This array of integers are down-converted by a naive envelopdetector and then down sampled by a factor of 8. The ECGsignal is then low-pass filtered using an IIR filter whosefrequency response is shown in Figure 4. The ECG signalis then displayed and stored in the phone.

Fig. 4. Frequency response of the IIR filter implemented

IV. RESULTS

Figure 5 shows the ECG signal as displayed on the screenof an Android phone. The PCB layout is shown in Figure 6. InTable II we detail the final bill of materials. It can be markedthat the final cost is much lower than the systems available inthe open market (as shown in Table I).

Fig. 5. ECG signal displayed on the Android phone’s screen

Fig. 6. PCB layout of the analog front-end

V. CONCLUSION

In this paper we have detailed an ECG monitoring systemusing smart-phones which we call SmartECG. There weremany design challenges in the project which were overcomeby a number of innovations as detailed in the paper. The

Fig. 3. Circuit diagram of the overall front-end

Component Quantity Costper

Cost($)

item($)

Passive components 1.2AD620N 1 8 8LM324N 1 2.5 2.5DC Power Jack 1 0.3 0.33.5mm Audio Jack 2 0.3 0.6AD633 1 13.2 13.23.5mm audio Jack 2 0.2 0.4Printed circuit board 1 30 30Self Adhesive Electrodes 1 2 2Total 58.2

TABLE IIBILL OF MATERIALS

inspiration of the work was to come up with a first phasecardiac monitoring system which should be easy to use andcheap enough to be affordable at village health centers ofunder-developed and developing nations. The first version ofSmartECG as detailed in this paper has been able to meet therequirements. In the next version we plan to make it furthercheaper and add feature extraction tools in the processingside of the system so that some of the major diagnosticfeatures can also be extracted and displayed in realtime onthe smart-phone screen (and if required then emailed to thecardiologist).

REFERENCES

[1] J. J. Oresko, Z. Jin, J. Cheng, S. Huang, Y. Sun, H. Duschl, and A. C.Cheng, “A wearable smartphone-based platform for real-time cardiovas-cular disease detection via electrocardiogram processing,” InformationTechnology in Biomedicine, IEEE Transactions on, vol. 14, no. 3, pp.734–740, 2010.

[2] J. Cano-Garcia, E. Gonzalez-Parada, V. Alarcon-Collantes, andE. Casilari-Perez, “A pda-based portable wireless ecg monitor for medicalpersonal area networks,” in Electrotechnical Conference, 2006. MELE-CON 2006. IEEE Mediterranean. IEEE, 2006, pp. 713–716.

[3] Q. Fang, F. Sufi, and I. Cosic, “A mobile device based ecg analysissystem,” Data Mining in Medical and Biological Research, pp. 209–226,2008.

[4] J. Ottenbacher, S. Romer, C. Kunze, U. Großmann, and W. Stork,“Integration of a bluetooth based ecg system into clothing,” in WearableComputers, 2004. ISWC 2004. Eighth International Symposium on, vol. 1.IEEE, 2004, pp. 186–187.

[5] “The heartcheck pen: a handheld ecg with smart monitoring,” Aug.2013. [Online]. Available: http://heartcheckpen.com/

[6] “Alivecor heart monitor,” Aug. 2013. [Online]. Available:http://www.alivecor.com/en

[7] “12-lead resting pc-ecg version: Cardioscape,” Aug. 2013. [Online].Available: http://www.bmm-medical.com/

[8] “Portable cardiocard mobile ekg machine comes with an android app,”Aug. 2013. [Online]. Available: http://www.phonearena.com/

ProductName

Product description Strengths Weaknesses Cost($)

Heart CheckPen

The Heart CheckPen is a compactportable ECGmonitor whichworks with twothumb contactelectrodes [5].

Heart check penis available overthe counter andis FDA approved.Heart check Pen canmonitor your ECGremotely over theinternet [5].

Only storesupto 20 heartrhythms [5].

276

AliveCor AliveCor is aniPhone case withbuilt-in fingercontact electrodeswhich are used totake the user’s ECGreading [6].

AliveCor hasautomatic syncingwith the patientsonline profile. It hasa separate batteryand therefore doesnot drain powerfrom the iPhone.It is compact anddoesn’t requirecables [6].

AliveCordoesn’t offercontinuousECGmonitoringover anextendedperiod oftime [6].

204

CardioScapePC-ECG

CardioScape is a 12-lead ECG monitorwhich displays re-sults on a PC [7].

Full 12-lead ECG.Automatic diagnosisof coronary heartdisease [7].

CardioScapeis not portableas it must berun with a PC[7].

397

CardioCardMobile

CardioCard Mobileis a portable ECGmachines that runsoff Android devicesvia bluetooth [8].

CardioCard is mo-bile and can be usedanywhere [8].

Highlypriced.

2 379

TABLE ICOMPARISON OF PORTABLE ECGS IN THE MARKET