Heart beat Sensor

Heart beat sensor is designed to give digital output of heat beat when a finger is placed on it. When the heart beat detector is working, the beat LED flashes in unison with each heart beat. This digital output can be connected to microcontroller directly to measure the Beats Per Minute (BPM) rate. It works on the principle of light modulation by blood flow through finger at each pulse.

Features

• Heat beat indication by LED

• Instant output digital signal for directly connecting to microcontroller

• Compact Size

• Working Voltage +5V DC

Specification

Parameter and Value

Operating Voltage - +5V DC regulated
Operating Current - 100 mA
Output Data Level - 5V TTL level
Heart Beat detection - Indicated by LED and Output High Pulse
Light source - 660nm Super Red LED

Pin Details

Board has 3-pin connector for using the sensor. Details are marked on PCB as below.

+5V - Power supply Positive input
OUT - Active High output
GND - Power supply Ground

Working

The sensor consists of a super bright red LED and light detector. The LED needs to be super bright as the maximum light must pass spread in finger and detected by detector. Now, when the heart pumps a pulse of blood through the blood vessels, the finger becomes slightly more opaque

and so less light reached the detector. With each heart pulse the detector signal varies. This variation is converted to electrical pulse. This signal is amplified and triggered through an amplifier which outputs +5V logic level signal. The output signal is also indicated by a LED which blinks on each heart beat.

Using the Sensor

• Connect regulated DC power supply of 5 Volts. Black wire is Ground, Next middle wire is

Brown which is output and Red wire is positive supply. These wires are also marked on PCB.

• To test sensor you only need power the sensor by connect two wires +5V and GND. You can leave the output wire as it is. When Beat LED is off the output is at 0V.

• Put finger on the marked position, and you can view the beat LED blinking on each heart beat.

• The output is active high for each beat and can be given directly to microcontroller for interfacing applications.

Applications

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

Sample Application: Digital Heart Beat Monitor

Let’s use this heart beat sensor and build a digital heart beat monitor. When a finger is put in the sensor, it displays the beats per minute (BPM) rate.

The pulse signal is applied to the P1.0 input of U2 that is AT89S52 (Can be any 8051 type) which is

monitored by the program whenever this input goes high. Internally to U2, there is a counter which counts how many 1ms intervals there are between two high going heart beat pulses. This number is then divided by 60,000 and the result is the pulse rate. For example, if the pulse rate is 60 BPM (beats per minute) there will be a pulse every second. The duration of one heart beat will be one seconds or 1000 x 1ms. Dividing 60,000 by 1000 will give the correct result of 60 which is shown on the display. If there is invalid result (BPM>200) it is invalid and waits for next cycle.