Thus the major requirement is to isolate that AC component as it is of prime importance. This signal is a DC signal relating to the tissues and the blood volume and the AC component synchronous with the heartbeat and caused by pulsatile changes in arterial blood volume is superimposed on the DC signal. The detector output is in the form of the electrical signal and is proportional to the heartbeat rate. The amount of light absorbed depends on the blood volume in that tissue. Some of the light is absorbed by the blood and the transmitted or the reflected light is received by the light detector. light emitted by the led, it either reflects (a finger tissue) or transmits the light (earlobe). When tissue is illuminated with the light source, i.e. The heartbeat pulses cause a variation in the flow of blood to different regions of the body. The basic heartbeat sensor consists of a light-emitting diode and a detector like a light detecting resistor or a photodiode. The flow of blood volume is decided by the rate of heart pulses and since light is absorbed by the blood, the signal pulses are equivalent to the heartbeat pulses. In the case of applications where the heart pulse rate is to be monitored, the timing of the pulses is more important. It measures the change in volume of blood through any organ of the body which causes a change in the light intensity through that organ (avascular region). The heartbeat sensor is based on the principle of photoplethysmography. Using a sensor: Heart Beat can be measured based on optical power variation as light is scattered or absorbed during its path through the blood as the heartbeat changes.However, pressure should be applied minimum and also fingers should be moved up and down till the pulse is felt. The procedure is to place the two fingers (index and middle finger) on the wrist (or neck below the windpipe) and count the number of pulses for 30 seconds and then multiplying that number by 2 to get the heartbeat rate.
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