This paper describes the design of a simple, low-cost microcontroller based heart rate measuring device with LCD output. Heart rate of the subject is measured from the finger using sensors and the rate is then averaged and displayed on a text based LCD.

The LCD of the heart beat monitor shows the beat per minute.The sensor part consists of sensing elements,LDR(light dependent resistor) and LED(light emitting diode),a comparator module,a low pass filter.Heart beat is sensed by the sensing elements and the comparator produces an amplified square wave output.The comparator output is given to a low pass filter and the filter output is fed to one of the digital inputs of PIC 16F877a type micro controller. The micro controller output ports drives the LCD.


This paper describes the design of a very low-cost device which measures the heart rate of the subject by clipping sensors on one of the fingers and then displaying the result on a text based LCD. Advantage of such a design is that it can be expanded and can easily be connected to a recording device or a PC to collect and analyse the data for over a period of time.

Heart rate measurement is one of the very important parameters of the human cardiovascular system. The heart rate of a healthy adult at rest is around 72 beats per minute (bpm). Athletes normally have lower heart rates than less active people. Babies have a much higher heart rate at around 120 bpm, while older children have heart rates at around 90 bpm. The heart rate rises gradually during exercises and returns slowly to the rest value after exercise. The rate when the pulse returns to normal is an indication of the fitness of the person.

Heart rate is simply and traditionally measured by placing the thumb over the subject’s arterial pulsation, and feeling, timing and counting the pulses usually in a 5 second period. Heart rate (bpm) of the subject is then found by multiplying the obtained number by 12. This method although simple, is not accurate and can give errors when the rate is high. More sophisticated methods to measure the heart rate utilize electronic techniques.

Block diagram for heart beat monitoring system

Electro-cardiogram (ECG) is one of frequently used and accurate methods for measuring the heart rate. ECG is an expensive device and its use for the measurement of the heart rate only is not economical. Low-cost devices in the form of wrist watches are also available for the instantaneous measurement of the heart rate. Such devices can give accurate measurements but their cost is usually in excess of several hundred dollars, making them uneconomical. Most hospitals and clinics in the UK use integrated devices designed to measure the heart rate, blood pressure, and temperature of the subject. Although such devices are useful, their cost is usually high and beyond the reach of individuals.


  • Digital Heart Rate monitor
  • Patient Monitoring System
  • Bio-Feedback control of robotics and applications
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