How To Make A Heart Rate Monitor Using LM358 IC | Heart Beat sensor

What is a Heart Rate Monitor?

A heart rate monitor is an electronic device that allows you to monitor your heart rate (ECG) for later use. They are most commonly used by medical personnel to monitor the heart rate of a patient, but nowadays they are rapidly becoming popular among many fitness centric people as it allows them to keep track of their heart rate during a workout session. heart rate monitor circuit functions on the principle of photoplethysmography: The change in the volume of blood in any organ causing a change in the light intensity through that organ. Here, A Light from an LED will be transmitted through any region of the body such as a finger and will then be received by an IR receiver. So, in today’s tutorial, we are going to go over a step by step procedure on How To Make A Heart Rate Monitor Using LM358 IC.

The heart of this circuit is an LM358 IC. LM358 is a dual op-amp IC integrated with two op-amps powered by a common power supply. It can be considered as one half of the LM324 Quad op-amp which contains four op-amps with a common power supply. It can handle 3 – 32V DC supply & source up to 20mA per channel. It’s available in an 8-pin DIP package

Hardware Required

You will need the following parts to build this project:

S.No	Component	Value	Qty
1)	Op – Amp IC	LM358	1
2)	IR LED	5mm	1
3)	IR Receiver (Photodiode)	–	1
4)	LED	5mm/3.5V	1
5)	Capacitors	4.7uF/100nF	2
6)	Resistors	10K, 47K, 680K, 6.8K, 220 Ohms	6
7)	Soldering Iron	45W – 65W	1
8)	Soldering Wire with flux	–	1
9)	DC Battery	9V	1
10)	Veroboard	–	1
11)	Battery clip	–	1
12)	Jumper wires	–	As per need

LM358 Pinout

Useful Steps

1) Solder the LM358 IC on the veroboard.

2) After that, solder a 680K resistor between pin 6 and pin 7 of the IC.

3) Now, solder a 100nF capacitor between pin 6 & pin 7 of the IC.

4) After that, solder a 47K resistor between pin 4 and pin 5 of the IC.

5) Now solder a 6.8K resistor between pin 4 and pin 6 of the IC.

6) After that, solder the -ve terminal of a 4.7uF capacitor with pin 5 of the IC and +ve with a 10K resistor.

7) Solder a 220Ohm resistor between pin 8 of the IC and the positive terminal of the IR transmitter LED. After that, solder another 220Ohm resistor between pin 7 of the IC and the +ve pin of Indicator LED.

8) Solder the +ve terminal of the indicator LED with the 220 Ohm resistor and -ve terminal with the GND of the IC (Pin 4).

9) Make two holes in a soft cloth clip using a soldering iron.

10) Fix IR transceiver pair in the holes.

11) After that, join together the photodiodes emitter terminal 7 the -ve pin of the IR transmitter LED together.

12) Solder the IR receivers collector terminal on the capacitor positive and the IR LED +ve with the 220 Ohm resistor (Pin 8) of the IC.

13) After that solder the +ve terminal of the battery clip with pin 8 of the IC and the -ve terminal with pin 4 of the IC.

Circuit Diagram

Working Explanation

This project can be used to perform small scale measurements. The working of this circuit is actually pretty simple. On placing your finger within the sensing clip, the IR rays reflect through as per the volume of blood in the blood vessels & capillaries. The reflected light is then received on the IR photodiode, sending an input control signal to the non – inverting input pin 5 of the Op-amp IC.

The LM358 IC amplifies the input signal & triggers the LED to blink. You can use a 9V battery to power this project. The blinking interval of the LED is controlled by the diminishing delay from the photodiode output.

Applications

• Used in healthcare and fitness facilities to measure the heart rate (ECG) of patients and athletes.

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