Published May 10, 2016

Heartbeat Monitor

This project produces a heartbeat graph using a photon and a heartbeat sensor through the blynk app.

BeginnerFull instructions provided3,145

Things used in this project

Hardware components

Particle Photon

uxcell® DC 5V Finger Heartbeat Sensor Detector Module

Breadboard (generic)

Software apps and online services

Blynk

Story

This project was done for my MEGR-3171 Instrumentation class at UNC Charlotte. I decided to make a heartbeat monitor that shows when a heartbeat is present. The sensor uses an infrared LED and a phototransistor to detect the pulse at the finger. The phototransistor is affected by pressure so constant pressure was required. Maintaining a constant pressure was one of the difficult parts because if the pressure is changing then the output values will change giving an unstable graph. To counter this I simply just froze my other finger against the back end of the phototransitor and avoided moving my fingers.

Due to the use of an infrared LED I had to make sure it was actually working since its invisible to the eye. To see the light I simply looked at the LED through my camera as shown below in figure 1.

Figure 1: Finger against the IR LED and the phototransistor

As you can seen in figure 1 there is light present on my finger meaning that it's turned on as it should be. In addition to making sure it turns on, I had to position the infrared LED so that most of the light hits the photransistor. Using the same method as mentioned previously, I adjusted the light while looking at it through the camera on my phone.

Once everything was setup properly and the code was functional, next was to get the data to be sent over the internet to a graph on my phone. For this project I used the blynk app which took me a bit to figure out. In the particle build, there is a code in the library that allows you to connect a project in the blynk app to your photon. Once this was done I created a graph and set it up to get data from pin A0 of the photon. After everything was done the graphs shown below were created.

Figure 2: Shows the graph in the blynk app without my finger on the sensor

Figure 3: Shows the graph in the blynk app with my finger on the sensor

As can be seen in Figure 2 and 3 the heartbeat monitor works (more or less) by giving a flat line when there is no finger present and then a peak at each heartbeat that occurs. I also tested to make sure that I was getting a proper heartbeat by checking my pulse and it seemed to be pretty accurate.

I was slightly dissatisfied with this sensor due to its inaccuracy and the amount of noise that occurs. For a future project I definitely plan on getting a better sensor and setting up an op-amp configuration to clean up the noise. Additionally, it proved rather difficult for me to get a bpm from this sensor due to my lack of programming knowledge.

Heartbeat Circuit Diagram

This schematic is simply the circuit used to get the heartbeat monitor display. The sensor is said to be used for an arduino; however, given that the sensor is made up of 2 resistors (one of high resistance and the other of low resistance), an infrared light, and a phototansistor, it seemed like it would be fine for use with a photon. On the sensor there are three pins labeled (+, -, and S). The (+) goes to the voltage source produced by the photon, the (-) goes to the ground of both the breadboard and the photon, and finally the (S) goes to the photons A0 pin. Additionally the voltage source for the photon is given through the USB connection.

Code

Heartbeat Code

Heartbeat Code

C/C++

The code gives an average value of the beat to give a slightly more accurate reading. As can be seen below in the code, it takes 75% of the old value and 25% of the new value and adds them up. The value that is calculated its displayed either though a graph or simply generating a list of numbers. However, using a list of numbers makes it difficult to find the peaks so graphing the values is a better option. Additionally, in lines 22-27 I believe is a filter of sorts for noise. Whenever I ran the code without these lines, the graph seemed a lot more unstable versus this bit in there.

Being the poor programmer that I am, most of this code was found online and I simply configured and added a couple things that I found to make it better.

int sensorPin=A0;
double alpha=0.75;
int period=50;
double change=0.0;
double max1=0.0;

void setup()
{
  Serial.begin(9600);
  delay(100);
}

void loop()
{
  static double oldValue=1009;
  static double oldChange=0.2;

  int rawValue=analogRead(sensorPin);
  double value= alpha*oldValue +(1-alpha)* rawValue;
  change=value-oldValue;

  if (change >= max1) {
    max1= change;
    Serial.println(" |");
  } else {
    Serial.println("|");
  }

  max1 = max1 * 0.98;

  oldValue=value;
  oldChange=change;
  delay(period);
}

Credits

Hussian Maanaki

1 project • 2 followers

Thanks to TkkrLab.

Heartbeat Monitor

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

Heartbeat Circuit Diagram

Code

Heartbeat Code

Credits

Hussian Maanaki

Comments

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Heartbeat Monitor

Heartbeat Monitor

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

Heartbeat Circuit Diagram

Code

Heartbeat Code

Credits

Hussian Maanaki

Comments

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