Arduino pulse sensor is quite commonly seen in various example projects using the typical sensor first made by pulsesensor.com. The sensor has a positive connection, a negative connection and an analogue data pin. It is quite easy to connect it with Arduino. pulsesensor.com has lot of examples and library of codes. For Mac, they have an app too. Pulse sensor module is important cheapest biomedical module. It is actually not sensitive, however basic can be learned through it. Pulse Sensor itself not digital, it is not interfacing through I²C or something similar protocol. It provides an analog value from 0 to 1023, pointing infrared the light sensor is receiving. When we place our finger between the IR LED and the light transistor of the sensor, as heartbeat dilates the blood vessels, it filters the light in pulsating manner. If the tide is properly calibrated then it may be enough sensitive.
Arduino Pulse Sensor Code
Arduino IDE has serial plotter (under Tool’s menu of IDE). Connect the sensor’s positive pin with 3.3V of Arduino, negative connection with GND of Arduino and the analogue data pin with A0 of Arduino. Just by using this code, you will get plot on Arduino IDE’s serial plotter :
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int sensorPin = A0; void setup() { Serial.begin(9600); } void loop () { while(1) { Serial.print(analogRead(sensorPin)); Serial.print('\n'); } } |
You’ll get plot with arbitary analogue value.
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To smoothen the graph, we can take a sample size, find the tide purely based on real life test (original code is by Johan_Ha on Hackster) :
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#define samp_siz 4 #define rise_threshold 4 // Pulse Monitor Test Script int sensorPin = 0; void setup() { Serial.begin(9600); } void loop () { float reads[samp_siz], sum; long int now, ptr; float last, reader, start; float first, second, third, before, print_value; bool rising; int rise_count; int n; long int last_beat; for (int i = 0; i < samp_siz; i++) reads[i] = 0; sum = 0; ptr = 0; while(1) { // calculate an average of the sensor // during a 20 ms period (this will eliminate // the 50 Hz noise caused by electric light n = 0; start = millis(); reader = 0.; do { reader += analogRead (sensorPin); n++; now = millis(); } while (now < start + 20); reader /= n; // we got an average // Add the newest measurement to an array // and subtract the oldest measurement from the array // to maintain a sum of last measurements sum -= reads[ptr]; sum += reader; reads[ptr] = reader; last = sum / samp_siz; // now last holds the average of the values in the array // check for a rising curve (= a heart beat) if (last > before) { rise_count++; if (!rising && rise_count > rise_threshold) { // Ok, we have detected a rising curve, which implies a heartbeat. // Record the time since last beat, keep track of the two previous // times (first, second, third) to get a weighed average. // The rising flag prevents us from detecting the same rise more than once. rising = true; first = millis() - last_beat; last_beat = millis(); // Calculate the weighed average of heartbeat rate // according to the three last beats print_value = 60000. / (0.4 * first + 0.3 * second + 0.3 * third); Serial.print(print_value); Serial.print('\n'); third = second; second = first; } } else { // Ok, the curve is falling rising = false; rise_count = 0; } before = last; ptr++; ptr %= samp_siz; } } |
With the above example, we given the example how really the thing works. Plotting only heart rate has not much value, yet it is good to test biomed project.
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