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    • Given that the information processing

    2018-11-05

    Given that, the information processing by the analysis software installed on the computer is performed digitally, it is necessary to convert the analog signal produced by the EKG-3DT to a digital format. The analog signal is received in the AN0 pin of the PIC18F2550, which has been previously enabled with the appropriate receive mode by the firmware resident in the program memory of the microcontroller. The firmware developed in C language enables pin AN0 to act as the input of an ADC. The analog to digital conversion is achieved through the flat crest sampling technique or instant sampling, which is obtained with a sample and hold circuit, and consists of multiplying the signal by a pulse train and storing the instant sample for the conversion cycle. The sampling frequency of the analog signals should be at least twice the input frequency, according to Nyquist’s theorem, in this case the ADC provides a minimal acquisition time of 0.97μs [8], but acquires a sample every 480μs which is sufficient for the bandwidth of the signal which is 120Hz. Although the output of the ADC has a length of ten bits, are used only the eight least significant bits to represent in digital form the electrical signal of the heart, since the corresponding electrocardiogram is stored inside the computer through a data file of thousands of data one byte each. The gnrh antagonist reached with eight bits is 19.53mV/bit and is enough for rebuild the electrocardiogram in digital form for their further processing by the computer. Once the information from the EKG-3DT is available in digital format, it is stored in the internal registers of the PIC18F2550 and sent to the computer using the standard USB 2.0. This process is complex and is controlled by the firmware stored in the program memory of the microcontroller. Fig. 9 shows the electronic diagram of the stage for the data communication between the EKG-3DT and the computer. In OS1 and OS2 terminals is connected a 20MHz quartz crystal and their respective 15pf capacitors grounded to set the oscillation that synchronizes the microcontroller operations. Serial output data are obtained through the microcontroller terminals D− and D+ in order to be transmitted to the computer via a connection cable USB using connectors type A and B at the ends. The USB protocol performs point to point communication, the host is represented by the computer and the hub is a peripheral device that, in this case, corresponds to the EKG-3DT and the data communication section. Because the USB initialization software is active at all times, USB devices can be added or removed at any time. Once the EKG-3DT and data communication section is added to the host, the device is enumerated by the USB initialization software and is assigned a unique identifier to use during the operation time [9]. The transaction type chosen to handle the data transmitted on the USB 2.0 standard is: interrupt. This type of transaction is suitable for the transmission of small data packets and is very reliable in applications such as the one presented in this paper. The data communication stage implementation inside the cabinet is illustrated in Fig. 10 and also can be seen in the upper right corner of the printed circuit shown in Fig. 7.
    Diagnostic software Conventional computer equipment is enough to execute the diagnostic software under Windows operating system and Labview development environment. The graphic environment and the diagnostic software, based on the information provided by the electrocardiogram, are implemented in a graphical programming system called Language G for Labview. This language is oriented towards virtual instrumentation, so Helper virus has many presentation tools with schematic features and adaptive methods [10]. Using these tools a program to capture, monitor, analyze and diagnose information from the EKG-3DT was developed. The software developed in this work to diagnose cardiac arrhythmias in humans consists of four stages: USB data reception, graphical user interface, analysis and diagnosis.