NAČRTOVANJE IN IZDELAVA ENOKANALNEGA EKG SISTEMA ZA UPORABO Z RAČUNALNIŠKO-MERILNO KARTICO RED PITAYA

KOSMAČ, MATEJ (author), Križaj, Dejan (mentor)

V sledeči diplomski nalogi visokošolskega strokovnega študija sem predstavil izdelavo vezja za enokanalni zajem EKG signala z uporabo sistema Red Pitaya. Amplitude signalov, ki jih s pomočjo elektrod odjemamo na površini kože so zelo majhne (milivoltno področje). Prav tako neizogibno zraven zajemamo tudi šum, poleg tega pa so v okolici prisotne motnje zaradi napajalnih vodov. Človeško telo se obnaša kot nekakšna antena. Problem zajema takih signalov je v tem, da potrebujemo način zajema, ki bo zmožen vse te motnje v največji možni meri izločiti. Ta ista metoda pa mora hkrati tudi ojačiti koristen signal. Elektrode, ki so prilepljene na kožo imajo različno dober kontakt s kožo, kar predstavlja še dodatno težavo. Za namen prikaza dovolj dobrega EKG signala sem izdelal vezje, ki opravlja funkcijo izločanja motenj, ojačenja šibkih, koristnih signalov in kompenzacijo različne prevodnosti med kožo ter elektrodo. To vezje uporablja instrumentacijski ojačevalnik kot predojačevalnik. Ta je zmožen ojačiti diferencialne signala, sofazne signale pa slabi. Rezultat tega je zelo dobro izločanje motenj, ki se pojavljajo kot sofazna napetost. Vezje za RLD z uporabo elektrode na desni nogi vsiljuje potencial ter s tem kompenzira lezenja (angl. drift) izhodne napetosti zaradi različno dobrega kontakta elektrod. Med razvojem vezja sem izdelal preprost generator EKG signala, s katerim sem vezje na koncu preizkusil. Tako sem imel znan ter definiran signal. Lahko sem izmeril signal na različnih stopnjah ter tako preveril, da vezje pravilno deluje. Generator je narejen v Matlabu, za generiranje vzorcev pa skrbi Red Pitaya. Zajem signala prav tako poteka s pomočjo Matlaba ter Red Pitaye; napetost prilagodi druga ojačevalna stopnja. Zajeti vzorci se matematično obdelajo z uporabo digitalnega filtriranja, kar sem prikazal na koncu diplomske naloge. Ugotovil sem, da je z uporabo dokaj preprostega vezja možno zajeti EKG signal, vsaj v domeni eksperimentiranja. Za dosego dobrega filtriranja pa je potrebno kar nekaj poizkušanja, da dosežemo dovolj kvaliteten signal.

• Language: Slovenian
• Keywords: EKG, Red Pitaya, Matlab, SCPI, instrumentacijski ojačevalnik, filtriranje signalov, zajem signalov
• Work type: Bachelor thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2015
• PID: 20.500.12556/RUL-72345
• Publication date in RUL: 14.09.2015

Secondary language

• Language: English
• Title: DESIGN AND DEVELOPMENT OF A SINGLE CHANNEL ECG SYSTEM FOR USE WITH A COMPUTER-MEASUREMENT CARD RED PITAYA

Abstract

In the following diploma thesis of the professional study programme I introduced the making of a circuit for one channel ECG signal acquisition using Red Pitaya system. Amplitudes of the signals, we acquire on the surface of the skin using electrodes are very small (millivolt scale). Inevitably we acquire noise as well; furthermore there are all kinds of disturbances, caused by power lines. Human body acts like an antenna. Problem of acquiring signals like that is that we need an acquiring method which will be able to remove those disturbances in the largest possible degree. That same method must amplify the useful signal at the same time. Electrodes which are stuck to the body have divergently good contact with the skin, which poses additional problem. For purpose of displaying a good enough ECG signal I developed a circuit, which does the function of removing disturbances, amplifies weak, useful signal and compensates for divergent contacts between the skin and the electrode. This circuit uses instrumentation amplifier as a preamplifier. It is able to amplify differential signals and attenuate common-mode signals. The result is very good elimination of disturbances that appear as common-mode voltage. RLD circuit enforces potential to the right leg using an electrode thus compensating the drift of output voltage. During the circuit development I made a simple ECG signal generator which was used to test the circuit. Thus I had a known and defined signal. I could measure signal at different stages to check if it operated correctly. The generator is programmed in Matlab and Red Pitaya is used to generate samples. Matlab and Red Pitaya are also used for signal acquisition; voltage is adjusted by the second amplification stage. Acquired samples are mathematically processed using digital filtering which I showed at the end of this thesis. I found out that it is possible to acquire ECG signal using simple circuit, at least for experimentation purposes. But a lot of attempts are needed to achieve a good enough filtering and a quality signal.

• Keywords: EKG, Red Pitaya, Matlab, SCPI, instrumentation amplifier, signal filtering, signal acquisition