Measure of the electro-cardiogram at a distance: Analog part
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Nowadays, the electrocardiogram is commonly detected between conducting electrodes points on the body in clinic or hospital, even if it has been recognized that the electrocardiogram can also be detected at a distance. This research focuses towards measuring the electrocardiogram of drivers in an automobile for the purpose of monitoring the driver's physiological condition. The variable position of the driver and the distance of the sensor from the subject add to the challenge of detecting the small signal in the presence of the interfering fields. The underlying objective is to develop a cheap and simple device capable of obtaining electrocardiogram at a distance. Further the data will be picked up for digital signal processing. The sensor used is considered a capacitive coupled electrocardiogram monitor. Electric field (AC E-field) sensors fabricated from ordinary electronic components have the high sensitivity required to measure the electrocardiogram E-field at a distance but the rejection of the ambient interfering fields is difficult. The sensor is mounted on the inside roof of the automobile, above the driver's head. The electrocardiogram voltage appears at the head and produces an electric field which is detected by the sensor. Alternatively, the head can be though of as one plate of a capacitor with the sensor as the other. In addition to the primary sensing electrode, we will add another capacitive coupled sensor the sensor and the two will be grounded. The signal we get from the second sensor will be inversed and subtracted from the primary signal, all that in order to eliminate the ambient noise. This will result in an electrocardiogram signal with greatly improved signal to noise. It is likely that a significant noise or interfering signal will still remain. This one will be removed in the second part of the research by an auto/cross-correlation process. Once we get the signal we will have to add an offset so that the AD converter (which can handle only positive value) can pick up all the values. Also included are the advantages and disadvantages, future research and improvements.