The electrocardiograph is an electronic

The electrocardiograph is an electronic device that captures and adjusts the heart’s electrical signals for their analysis and study. The electrocardiograph developed in this research is called EKG-3DT (diagnostic electrocardiograph with three bipolar derivations). When the heart beats, many excitable purchase Pirfenidone depolarize simultaneously and cause a voltage in the range of −2mV to 2mV around the heart [2]. To the surface of the skin is spread this biopotential, but by the time it reaches the skin surface the signal has been attenuated. This electrical potential can be positive or negative, being the reference for measuring the skin surface. The electrical potential of the heart comes from the ventricular muscle, with each beat of the membrane the potential raises from a slightly negative value of approximately −0.25mV to a positive value nearly 1mV, consequently the EKG-3DT sensors on the skin receives as input information an electrical signal with amplitude close to 1.25mV [2]. By the other hand, the output of the EKG-3DT produces an analog signal with the same information generated by the electrical potential of the heart, but filtered and with an amplitude in the range of 0–5VDC, which is the input signal to the data communication block. In order to generate the electrocardiograms, the EKG-3DT section that captures the electrical signals uses three surface electrodes, which should make contact with the skin in electro-permeable points on both upper limbs and on the lower limb, by taking the connection criteria for the Einthoven’s Triangle in the configuration of the bipolar derivations II, as seen in Fig. 5. The processing of the heart electrical signals sensed by the transducer is implemented in the following order: amplifying, filtering and coupling, as shown in the block diagram of Fig. 6. The electrical signals collected by the transducers with a bandwidth in the range from 0.03Hz to 150Hz are amplified and added by instrumentation amplifiers type AD620A and AD705J with an appropriate common-mode rejection ratio (CMRR) of 114dB and 123dB respectively. The filtering for the pre-amplified signal is performed by a Sallen Key high-pass filter (HPF) with a cutoff frequency of 0.03Hz, and a second order low-pass Butterworth filter (LPBF) with a cutoff frequency of 150Hz. These filters are implemented using operational amplifiers OPA4277PA that eliminate noise components and attenuate the aliasing effect for the sampled signal. The next part is a standard offset adder configuration for signal to add a DC component to the original signal in order to adjust the voltage active range for the input signal [5,6]. The coupling of the signal for the analog to digital conversion, which is received by the data communication block, is performed by means of a limiter circuit in the active range from to 5V, it is implemented by a pair of Germanium diodes 1N60 and a Zener diode 1N4732A that ensures an input protection for the analog to digital converter (ADC) included in the data communication stage. The EKG-3DT includes a conventional regulated voltage source to supply 5VDC and −5VDC to be connected to the electrical power commercial network of 120VAC. The system can also operate by means of eight commercial type D batteries housed inside the cabinet of the EKG-3DT. In addition, the EKG-3DT has shock protection by isolating the voltage source using ISO124 standard [7]. The physical implementation of the electrocardiograph inside of the cabinet is illustrated in Fig. 7.
Data communication The device for communicating data between the electrocardiograph and the computer equipment has two sections as shown in Fig. 8: one ten-bit ADC and the hardware for communication using USB 2.0. Both functions are performed by the popular PIC18F2550 microcontroller, manufactured by Microchip Technology Company that by its characteristics in economics, functionality, availability, low power consumption and reliability is widely used for these purposes. The stage for the data communication is housed in the EKG-3DT cabinet, but gets its power supply via the USB connection cable connected to the computer. Consequently, the data communication section only receives an analog voltage signal in the range 0–5V, coming from the outlet of the EKG-3DT, that contains all patient information to show the corresponding electrocardiogram on the monitor of the computer, and there is not energy consumption from the batteries or from the EKG-3DT voltage source.