Heart rate sensor

Abstract

This project is to develop a heartbeat rate sensor. It makes use of photoplethysmography which is a non-invasion and unobtrusive technique to measure heart rate from the surface of the skin. An integrated sensor composed of an infrared light emitter and a phototransistor is used to sense the heart beat signal reflected from blood vessels. When a fingertip is placed over the sensor, the infrared from the light emitter is reflected by blood vessels back to the phototransistor. Therefore, it is a reliable and simple method to monitor the heartbeat rate without penetrating into skin. It is also low cost. As the signal received is very weak, so, it first passes an amplifier to increase the signal strength before using band-pass filter to filter out the unwanted signal outside the range of 0.7 Hz and 5 Hz. This is a two-stage filter and the gain is about 100 for each stage. The signal is then ended up with a large enough output. After that, Bluno, a type of Arduino, is used to do the signal conversion and transmission. The output of the circuit is connected to the Bluno board. It converts the analog signal to a digital signal and sends out the digital signal to a mobile device through Bluetooth. This wireless feature makes the sensor more convenient and user friendly than traditional measuring devices.