Heart Rate and EKG Monitor using the MSP430FG439:This application report describes how to build a digital heart rate monitor using a MSP430FG439 microcontroller (MCU). The heart beat rate per minute is displayed on a LCD glass. In addition to this the application outputs digital data stream via RS232 serial port to allow EKG waveform display on a PC. PCB Gerber files, schematic, bill of materials and firmware are provided in a zip file associated with this application report.The entire application runs using a CR2032 3-Volt lithium battery.
An electrocardiogram (ECG) also called EKG is a graphic tracing of the voltage generated by the cardiac or heart muscle during a heartbeat. It provides very accurate evaluation of the performance of the heart.The heart generates an electrochemical impulse that spreads out in the heart in such a fashion as to cause the cells to contract and relax in a timely order and thus give the heart a pumping characteristic.This sequence is initiated by a group of nerve cells called the sinoatrial (SA) node resulting in a polarization and depolarization of the cells of the heart. Because this action is electrical in nature and because the body is conductive with its fluid content, this electrochemical action can be measured at the surface of the body.
An actual voltage potential of approximately 1mV develops between various body points. This can be measured by placing electrode contacts on the body. The four extremities and the chest wall have become standard sites for applying the electrodes. Standardizing electrocardiograms makes it possible to compare them as taken from person to person and from time to time from the same person. The normal electrocardiogram shows typical upward and downward deflections that reflect the alternate contraction of the atria (the two upper chambers) and of the ventricles (the two lower chambers) of the heart.A typical single cardiac cycle waveform of a normal heartbeat is shown in Figure 1-1. The voltages produced represent pressures exerted by the heart muscles in one pumping cycle. The first upward deflection, P, is due to atria contraction and is known as the atrial complex. The other deflections, Q, R, S, and T, are all due to the action of the ventricles and are known as the ventricular complexes. Any deviation from the norm in a particular electrocardiogram is indicative of a possible heart disorder.In this application report the EKG waveform is used by the MCU to measure the heart beat rate. Because heart beat calculation is the major focus the electrodes are simplified to two connections one to a right arm and the other to the left arm. This type of set up can be frequently seen in exercise machines such as
a treadmill.