Wireless Heartbeat Monitoring system uses AT89S51 microcontroller, RF transmitter Receiver and IR Heart beat sensor. The device senses the heart rate from the finger tip using IR reflection method and displays it on a LCD display in beats per minute. The circuit has an accuracy of 4 beats per minute and it is very easy to use. In medical terms, the technique used here for sensing heart rate is called photoplethysmography.
Photoplethysmography is the process of optically estimating the volumetric measurement of an organ. Pulse oximetry, cardiovascular monitoring, respiration detection, heart rate monitoring etc are few common applications of photoplethysmography. Let us have a look at the application of photoplethysmography in heart rate monitoring from the figer tip. When the heart expands (diastole) the volume of blood inside the finger tip increases and when the heart contracts (systole) the volume of blood inside the finger tip decreases. The resultant pulsing of blood volume inside the finger tip is directly proportional to the heart rate and if you could somehow count the number of pulses in one minute, that’s the heart rate in beats per minute (bpm). For this an IR transmitter/receiver pair placed in close contact with the finger tip. When the heart beats, the volume of blood cells under the sensor increases and this reflects more IR waves to sensor and when there is no beat the intensity of the reflected beam decreases. The pulsating reflection is converted to a suitable current or voltage pulse by the sensor. The sensor output is processed by suitable electronic circuits to obtain a visible indication (digital display or graph).