Image Processing Reference
In-Depth Information
Fig. 7. Data Acquisition Module Circuit
3.2 Acquiring and processing ECG signal
The acquisition data stage has a hardware part composed by the A/D converter, and a
software part which is in charge of directing the A/D converter work. Any programming
language allowing low level hardware instruction is usable. (Vidal & Pavesi, 2004) and (Vidal
& Gatica, 2010) describe the use of C and Visual Basic programming languages for getting and
processing the ECG signal. According to these works, the routine written in C language is used
to direct the A/D converter functioning using non-standard functions to access the personal
computer ports. The obtained quantity of samples is stored in a binary file which is rescued by
the Visual Basic programming language routine to processing (applying filters and QRS
detection algorithms) and showing the signal. Showing the signal at the computer is done “off-
line” from the generated file with the ECG signal samples. As (Vidal & Gatica, 2010) highlights
using current high level programming languages would be possible to build a showing
graphics routine. Using lineal interpolation it is possible to get high level graphic results. Even
though the Nyquist's sample theorem indicates that a signal can be rebuild using an ideal
interpolation method (Lindner, 2009; Proakis & Manolakis 2007), by means of lineal
interpolation, and through this it is possible to get good results for low frequency signals like
ECG. It is possible to build a universal graphics generator for getting signals (Vidal & Pavesi,
2004; Vidal & Gatica, 2010). Figures 8 and 9 present a universal graphics generator for a sine
curve signal and a triangle signal, respectively. These signals are low frequency signals (2 Hz)
generated by a function or electrical waves generator with some acquisition deformities (high
negative values are not considered). Figure 10 shows a pure ECG signal got by means of an
implemented ECG system (Vidal & Gatica, 2010).
Fig. 8. Sine Signal obtained by the A/D Change Module
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