The invention relates to a portable wireless apparatus for monitoring heart activity comprising a detachable supporting element fastened to the user's body, at least two sensor electrodes fastened on said supporting element, a signal processing unit connected electrically to the sensor electrodes and including an analogue-to-digital converter stage, a filtering stage, an amplifier stage, a microcontroller and a radio-frequency transceiver stage, and a processing, management and display unit being in wireless communication connection with said signal processing unit.

Temporary or continuous examination of specific health parameters of individuals is an activity that has been known for a long time. Besides transmitter units comprising one or more sensors and mostly processor-based receiver devices, many intentionally simpler, informative apparatuses and methods have become known recently, due partly to the growth of health awareness, that aim at assisting users to obtain information on their general state of health, fitness or the parameters of specific organs as the case may be that satisfies their curiosity on the one hand and help them contact the appropriate health care institution or request targeted assistance if necessary.

The past decade saw the spread of systems or arrangements comprising one or more sensors to be fixed on the human body and a receiving and evaluating device connected to the sensors) and implemented, with the spread of smart phones, increasingly by applications running on them and exploiting their relevant functions, ranging from the early instruments of this type - such as the mechanical pedometers, for instance - to apparatuses, mostly large and cumbersome, but sometimes also portable ones used decisively by health care institutions.

Initially, the sensor unit and the receiving and evaluating unit had been in wired connection; recently, this has been relegated into the background almost completely, and the sensor unit - that may, of course, comprise several sensors - and the control unit - that is itself the processor unit - are in wireless connection, enabled not in the least by the energy sources, i.e., batteries, powering said sensors. In smart phones, wireless connection means mostly the most common Bluetooth connection but, of course, any other proprietary connection is also conceivable, provided that the manufacturer of the device gives special emphasis, e.g. to having a highly secure, inception-free connection. Long-term monitoring with the traditional ECG technique is feasible only with disposable electrodes filled with so-called conductive gel, something that is contrary to the requirement of simple putting on and wearing, and may significantly raise the monitoring costs. For example, setting the optimum regimen of an overloaded patient may take up to one month, at two electrodes to be discarded by day.

Let's underline among the parameters subjected to monitoring and supervision the detection and monitoring of the pulse rate, the body temperature, the cardiac function and the quantity of exercise. The sensors ever are associated with, or fixed on the body of the person concerned in themselves or with the help of some supporting element, in line with the monitored parameters.

In terms of importance, heart rate and cardiac monitoring stands out among the monitored parameters. This is being done nowadays most commonly by fixing one or two electrodes in communication with the receiver and processor apparatus at appropriate places of the body. For the sake of simpler and more convenient wearing over a longer time, devices comprising a belt, easy to fix and wear on the human body, the chest, and one or several sensors fastened to the belt or arranged in it have spread in this category. Whereas previously adequate skin-to- sensor contact had to be ensured, making the use of a gel indispensable in most cases, now the so-called dry capacitive sensors, without such drawbacks, have started to spread.

The work by E. Sardini, M. Serpeloni entitled "Instrumented Wearable Belt For Wireless Health Monitoring" published at the Eurosensor XXIV Conference, September 5-8, 2010, Linz, Austria provides a comprehensive discussion of state-of-art technology, including the wireless connection of the chest belt to an evaluation apparatus that may be a smart phone for that matter. This document includes an example where the signals of the electrodes are first amplified, then filtered, and the signals so prepared are led to a special integrated circuit of type INA333, the signal of which is then processed according to the technical specifics and transmitted to the receiver unit. This document may be considered representative of the state of the art, and it demonstrates the general and unanimous professional belief concerning the matter.

US 20040068195 Al also discloses an ECG monitoring device wearable on the chest, in wireless connection with a receiver, processor and display unit. Accordingly, the electrodes are di- rectly connected in the known and usual way to a low-power low-noise operational amplifier that amplifies the differential signal of the electrodes and the signal being processed this way is forwarded to a filtering stage that is meant to filter out the 60 Hz noise.

An article entitled "A Low-Power Portable ECG Sensor Interface With Dry Electrodes" published in May 2013 in Vol. 34., No.5. of the Journal of Semiconductors treats the use of dry electrodes in detail. The document that names many specifics, measurement results and values discloses only that the electrodes need to be connected to an analogue front-end stage that is suitable for producing signals suitable for further processing from the differential signals of the electrodes.

The document WO 2008/120950 Al describes a single-channel portable wireless ECG monitoring apparatus and method. Figure 8 of the document and the related description present an operational differential amplifier at the input of the apparatus, and it is a differential signal that is amplified by it that is then filtered, amplified and further processed in the known and usual way. The document provides no hints for the selection of the suitable or applicable electronics.

Figure 4 of US 6,149,602 shows dry electrodes disposed on a chest belt that are, according to the description, connected to an operational amplifier for the ECG signal, specifically, as shown in Figure 5, through an input protection circuit that protects the electronics against any high-voltage signals. The document includes no instruction or recommendation for the electronics to be applied or used.

US 8,543,195 Bl describes ECG sensing with noise filtering. At least two electrodes are used to sense the ECG signals, with a denoising stage coupled to their output that processes and digitises the ECG signals, then the signals processed this way are processed by a processing stage, providing further noise filtering, and the resulting signals are transmitted by a communication stage to a remote device. The document does not cover specifically the type of electronics to be used.

The object of the present invention is to create a portable wireless heart-monitoring apparatus which, although not a diagnostic tool, can provide almost medical-quality ECG data, e.g. precise pulse rates, data characterising the motion of the user and respiratory rates, that can function reliably and produce adequate measurement results at a lower cost thanks to its simpler structure. Our object is, moreover, to enable user monitoring for up to 12-24 hours in a way that makes any status change detectable "on-line, just in time" to be able to take the necessary measures in time.

Our object is, moreover, to make the sensor unit of the apparatus easy to put on and take off, suitable for being worn also under the clothing, during work or at night, without impeding the target person's sleep. This means that the apparatus must have small dimensions, notwithstanding that long-term monitoring requires batteries of a higher capacity and hence of a larger size.

To produce ECG signals of satisfactory quality, the same tasks need to be solved during signal processing as in the traditional case, albeit with different means. The novelty of our solution lies in the recognition that, from the point of view of signal processing, the the output voltage of the active dry electrodes approximately five times higher than the traditional ones matches so perfectly an integrated circuit with excellent parameters, developed for a totally different purpose, that all of the latter's advantageous properties can be utilised to almost 100 percent. That circuit has been developed expressly for processing the extremely small signals of bridge-connected sensors (load and mass measurement cells implemented by strain gauge, semiconductor cells, platinum-based thermometers etc.).

One of the main novelties of the apparatus according to the invention is that an essential part of the signal processing unit communicating with the sensor unit on the body of the user is implemented by an integrated circuit developed for an expressly different purpose, ensuring signal processing that is simpler and provides better results. It is a further advantage that the sensor electrodes are not connected to the signal processing unit directly, but already through a filtering stage each, that has or may have a favourable effect on the operation of the signal- processing unit. The smart phone or tablet in wireless connection with the sensor and transmitter unit is needed not only for data transmission, but also to take over computing-intensive tasks implying no problem for a normal multi-core processor tool from the microcontroller of the sensor unit running on low clock pulse to reduce power consumption. These include e.g. the filtering of the 50 Hz noise remaining in ECG signals, etc.

Based on the recognition outlined above, the task has been solved via a portable wireless apparatus for monitoring heart activity according to the features of independent claim 1. Pre- ferred embodiments are disclosed in the dependent claims.

These and other aspects of the invention will be described in further detail, particularly with reference to one or more of the following figures which describe a certain preferred embodiment of the invention. In the drawing,

Figure 1 shows the typical structure of a traditional apparatus at block diagram level,

Figure 2 shows the structure of an advantageous embodiment of the apparatus according to the invention, also at block diagram level,

Figure 3 shows a possible, more detailed, connection diagram of the input stage of the apparatus according to Figure 2,

Figure 4 shows a possible connection diagram of the microcontroller of the apparatus according to Figure 2,

Figure 5 shows a possible implementation of the Bluetooth communication stage of the apparatus according to Figure 2, and

Figures 6-7 represents a possible realisation of the supplementary stages needed for the operation of the apparatus according to Figure 2 at connection diagram level.

Our objective is to build the differential signal of the two contact points and to amplify it to the level suitable for evaluation. Therefore, the extremely small electric signals received at the two measuring points are amplified and a differential of the left-hand and right-hand contact points is provided, and the signal is further amplified to the level where it can already be processed well. The human body, acting as an antenna, picks up noise from the surrounding electromagnetic field that can exceed by one or two order(s) of magnitude the useful signal, so that said noise shall be eliminated by a so-called notch filter of 50 or 60 Hz. In terms of signal processing, we have so far spoken of analogue technology. Today, the devices used for visualisation - tablets, mobile phones - are already almost exclusively digital, so the analogue signals are digitised and transmitted to the processing and display devices in some standard, predominantly wireless, way at this level.

Figure 1 therefore shows a solution representing state-of-the-art technology at block diagram level. Electrodes 1 and 2 placed on the user's body pick up the very small bioelectric poten- tials generated by the heart. Electrodes 1 and 2 are led connected to the differential positive and negative inputs of a special, in most cases operational amplifier 3 e.g. of type INA333. Besides the useful signals, radio frequency interference and, with much higher amplitude, the 50 Hz interference of the surrounding electric network are also present, that would make it impossible to produce a correct ECG diagram. The inputs of operational amplifier 3 are provided with integrated noise suppression against radio frequency interference, and the 50 Hz noise (present at both inputs in the same phase) is significantly, but not yet satisfactorily dampened by the min. 100 dB common mode suppression of the operational amplifier. Consequently, amplification by the first amplifier stage must be limited due to the potential overdrive. The output of operational amplifier 3 is connected through a notch filter 4 of 50 Hz and a band-limited amplifier 5 to the input of an analogue-to-digital converter 7. The characteristic ECG signal shape makes it possible to keep the so-called zero line automatically near zero level. This objective is achieved by a negative feedback of the output of operational amplifier 3 to the REF input of the same amplifier 3 that comprises a serially connected R2 resistor and CI capacitor connected parallel to a Miller integrator 6 that is realised by another operational amplifier. The notch filter 4 ensures a further min. 40 dB reduction of the 50 Hz noise; at a bandwidth of a few Hertz that will only filter out the 50 Hz components of the useful signal, so the distortion of the ECG signal shape is negligible.

The band-limited amplifier 5 raises the signal level by around 40 dB; with its 120 Hz breakpoint it fulfils the anti-aliasing filter function needed for digitisation. The 16-bit bipolar analogue-to-digital converter 7 is connected to a microcontroller 8, the latter controlling the analogue-to-digital converter 7 through an SPI bus. Its minimum sampling frequency is 400 Hz. Output TX and input RX of the microcontroller 8 are connected to the input of subsequent low-energy Bluetooth module 9, controlled as a matter of course by microcontroller 8 through a TTL level serial line, and connected through the antenna of Bluetooth module 9 to a receiver and processor unit well known for a person skilled in the art and not shown in the figures.

With the appropriate selection of the components, the unit constructed this way has very low consumption, but it requires numberless capacitors and resistors in addition to the operational amplifiers that obviously increase the physical dimensions of the electronics. It is also a problem that, with a notch filter 4 constructed with double T-units, the sufficiently precise centre frequency can only be maintained by elements of 0.5-1% tolerance, implying significant addi- tional costs and procurement difficulties. These factors aggravate also the mass production of the apparatus.

Figure 2 shows a possible embodiment of the transmitter unit altered according to the invention relative to Figure 1, at block diagram level. As can be seen, electrodes 11 and 12, preferably EPIC dry electrodes, are connected to an input pre-amplifier stage 15a of an integrated circuit 15 through radio-frequency interference filter + anti-aliasing low-pass filters 13, 14 built up of passive parts. The integrated circuit 15 applied in the present example is manufactured by several companies, but Chipress' type CS553xBZ has the best parameters among them, as it comprises all the functional elements that are indispensable for producing an ECG signal: the best commercially available programmable, low-noise pre-amplifier stage 15a with bipolar differential inputs, a 24-bit sigma-delta analogue digital converter stage 15b that can produces 18-bit noise-free resolution even at the sampling speed applied here (800 sample/s), a digital filtering stage 15c that could only be realised with similar parameters in analogue mode at very high cost, and an SPI bus 15d. The common mode suppression of the input preamplifier stage 15a exceeds 100 dB, suppressing significantly the 50 Hz line frequency arriving in common phase during the subtraction of the signals of the two connections. Owing to the location of the active sensors, not represented here, and the deviation of the output amplifiers, the signals arriving to the two inputs will never be completely identical, so the differential signal will always incorporate 50 Hz components. The residual 50 Hz noise is suppressed by a so-called Sync. FIR digital filtering stage 15c adapted to the sampling frequency that acts as a much more precise notch filter than the analogue solutions due to the crystal precision of the oscillator of integrated circuit 15. The parameters of the integrated circuit 15 are set and the results read with the help of SPI bus controller 15d directly with a microcontroller 16.

Since the integrated circuit 15 requires very few external elements, in addition to ensuring a signal shape of higher quality, the unit constructed this way can be built altogether from around one third of the parts, implying also much smaller integrated circuit dimensions. This solution is also more favourable for mass production, since the deviation of the passive elements exerts no particular influence on the signal shape. The microcontroller 16 is connected to a Bluetooth module 17 in the usual way, and the latter is connected through its own antenna to a receiver and processor unit that is not represented in this figure.

In Figures 3-7 you can see the more detailed connection drawings of the sensor and transmit- ter unit of the exemplary apparatus according to the invention, presented at block diagram level in Figure 2. Note that the connection presented there is shown solely by way of example; persons skilled in the art may create different embodiments based on the publicly available technical literature and product specifications, in the light of their relevant general knowledge.

As can be seen in Figure 3, the integrated circuit 15, e.g. of the type CS5532BS as mentioned above, is connected on the one hand to an oscillator U8 of type 74LVC1GX04 in the usual way and, on the other hand, through the low-pass filters indicated in Figure 2, to the electrodes not shown in the figures. Connectors CN3 and CN4 fulfil this purpose. Low-pass filters 13, 14 are led to the inputs AIN1+ and AIN1 - of the integrated circuit 15 through ferrite coils FT4 each, through the serially connected capacitor C29 - resistor R25, and capacitor C30 - resistor R26 resistor units, respectively, bridged on the one hand also by capacitor C26, and connected to a ground potential through a resistor R27— capacitor C23 connected parallel to each other and a resistor R28 - capacitor C25 member, respectively. Connectors CN3, CN4 provide the ground potential and the symmetrical supply voltage of the sensors through their connector pins a, b. Input OSC2 of integrated circuit 15 is connected through resistor R20 to output Y of the oscillator U8 mentioned above, and in the present case a crystal X2 provides a frequency of 4.9512 MHz.

Figure 4 allows to trace, basically, the connection of the microcontroller 16. As can be seen, input RA4 and output RC3 of microcontroller 16 that can be implemented e.g. by a microcontroller of type PIC32MX150F128D are connected through resistors R22, R23 each to the SDO output and SDI input, respectively, of the integrated circuit 15. Output RB4 of microcontroller 16 is in the present example connected to the control input of a solid state switch T4 of type FDV301N, controlling a buzzer Zl manufactured by ZUM5, the other connector of which is connected to the supply voltage of the system. An interface for the microcontroller 16 needed for programming is ensured by connector Jl .

Figure 5 outlines a possible connection of Bluetooth module 17 providing for the Bluetooth communication of the apparatus shown in Figure 2. CTS input and RTS output of a circuit Ul of type HC05 are connected to output RCI and input RA9, respectively, of microcontroller 16, and according to its manufacturing documentation, it ensures the wireless transmission of the signals connected to it. The operation of circuit Ul is confirmed by LED D6 connected to its output PI08 through a resistor R17, and by a LED D7 connected to its output PI09 through a resistor Rl 8, where the latter is meant to display the paired status of the system, whereas the former shows the status of the Bluetooth module 17 by blinking in a known manner. A jumper CN6 provides for switching between the programming and operational mode of Bluetooth 17. A circuit U5 of type LP3985 generates the adequate power supply, needed also for circuit Ul, from the power supply of the system, whereas in the present case a restart of circuit Ul is ensured by a solid state switch T3.

Figure 6 shows possible circuit diagrams of two essential additional stages: circuits U9, U10 of type FM25V20 used as memory are shown in the upper part of the figure, an output SO of said circuits is connected to an input RA1 of the microcontroller 16, an input CS- is connected to outputs RC6 and RC7 of the microcontroller 16 and also connected to the power supply via resistors R33, R34, and they receive the clock pulses needed for operation through their SI inputs connected to output TB2 of the microcontroller 16, and inputs SCK commonly connected to output RB 14 of the microcontroller 16. It is an essential feature of circuits U9, U10 applied here that, as compared to the circuit components used normally for storage, they can perform more write/read cycles by an order of magnitude without breakdown and at high speed.

The operation of the unit is promoted by a real-time clock constructed in the usual way with a circuit U12 of type MPC79411 and an acceleration sensor implemented by a circuit Ul l of type MMA8652FC, connected to outputs RB8, RB9 of the microcontroller 16 through their common inputs SDA and SCL, respectively.

Figure 7 shows a circuit U4 of type LT3032 generating the supply voltages needed for the symmetrical power supply of the apparatus according to the invention with great precision, that receives its input voltages through its inputs INN1 and INP from an oscillator circuit U3 of type TC7660S that generates from the positive voltage VSYS led to its input V+ a voltage -VSYS of identical size and opposite polarity. A DC voltage of 3.3 V needed for the operation of the apparatus is produced from this voltage VSYS by a voltage-regulation circuit U7 of type LP3985.

Powering the several units and stages of the apparatus presented above has been ensured in the present example by lithium-polymer batteries, so the apparatus comprises also a charging stage to ensure the appropriate charging of the batteries. The requirements of charging lithium batteries are met in the present example by a charging circuit U2 of type MP2607, connected through a connector CN2 to a Li-Po cell applied as battery, whereas its input INI is connected to a charger connector CNl that is a usual adapter connector, providing for the use of the common, normal AC chargers. The apparatus presented here can be switched on and off by a pressure switch Kl, connecting through a resistor R7 and a diode D4 the outputs SYS1- SYS2-MODE of the charger circuit U2 and through a diode D5 the input RBI 3 of the microcontroller 16 to the ground, controlling thereby the microcontroller 16 to execute the switch- ing-on and switching-off processes. Microcontroller 16 controls through its output RA10 a solid state switch T2, enabling the grounding also the anode contact of diode D4, as well as the control electrode of the solid state switch Tl, switching off thereby the voltage VSYS.

The status of the charger circuit U2 is indicated in the present example by a LED D2 connected to the output STAT1- of the charger circuit U2 through a resistor R5 and a LED D3 connected to the output STAT2- output of the charger circuit U2 through a resistor R6, indicating the charging process and its termination.

In the case shown, a maximum 24-hour-monitoring will not mean continuous recording of the ECG curve, since the resulting data mass would be practically unmanageable. Therefore, although the apparatus monitors the ECG signals continuously, it determines the mean pulse rate and the minimum and maximum deviation from the mean for an adjustable period. Similarly, it provides the average respiration rate and the type of movement of the user, e.g. resting, moderately moving, maybe lying down etc. If the pulse rate deviates from a figure accepted for a given person, in addition to the usual packet acknowledgement a command will be issued for collecting the ECG data for a predefined period of time, and to create a packet in which the other parameters are also present with satisfactory frequency. Higher data traffic causes rise of consumption, so one can only request more frequent ECG packets in justified cases, taking into account also the reduction of the monitoring period. Given the continuous monitoring and evaluation, the storage capacity of the apparatus can only prevent data loss due to communications errors, offline data sampling (without mobile phone) is not possible, that is, no data query is possible after a day has passed, because is not the objective of the apparatus or the application. Having said properties the apparatus is a measuring device supporting status indication and lifestyle changes and their maintenance.

The novel measure previously unknown in this special field is that the generation of the dif- ferential value is done directly, by a time-tested measuring technology device developed for a different purpose, without pre-amplification and digitisation, where the apparatus also performs the filtering of network noises with very good parameters. This signal can already be transmitted to the receiver and processor unit, expediently a mobile phone with an enormous computing capacity will easily cope with any remaining noises.

List of used reference signs

1 electrode R7 resistor CN2 connector

2 electrode R17 resistor CN3 connector

3 operational amplifier R22 resistor CN4 connector

4 notch filter R23 resistor Ul circuit

5 band-limited amplifier R25 resistor U2 charger circuit

6 Miller integrator R26 resistor U3 oscillator

7 analogue-to-digital conR27 resistor U4 circuit

verter R28 resistor U5 circuit

8 microcontroller R33 resistor U7 voltage regulator cir¬

9 Bluetooth module R34 resistor cuit

11 electrode CI capacitor U8 oscillator

12 electrode C23 capacitor U9 circuit

13 low-pass filter C25 capacitor U10 circuit

14 low-pass filter C29 capacitor Ul 1 circuit

15 integrated circuit C30 capacitor U12 circuit

15a pre-amplifier stage Kl pressure switch FT4 ferrite coil

15b digital converter CN6 connector AIN1+ input

stage Jl jumper ΑΓΝ1- input

15c digital filtering stage D2 LED CS- input

15d SPI bus D3 LED CTS input

16 microcontroller D4 diode INI input

17 Bluetooth module D5 diode INN1 input

R2 resistor D6 LED INP input

R5 resistor D7 LED OSC2 input

R6 resistor CN1 connector PI08 output PI09 output T2 solid state switch

RA1 input T3 solid state switch

RA4 input T4 solid state switch

RA9 input VSYS voltage

RA10 output -VSYS voltage

RB4 output X2 crystal

RB8 output Zl buzzer

RB9 output

RBI 3 input

RBI 4 output

RC1 output

RC3 output

RC6 output

RC7 output

RTS output

SCK input

SCL input

SDA input

SDI input

SDO output

SI input

SO output

ST ATI - output

STAT2- output

SYS 1 output

SYS2 output

MODE output

TB2 output

V+ input

Y output

a, b, c contact

Tl solid state switch