This is my sketch and my serial monitor output. Why is the current_time variable showing 0 when it should be increasing with time? unsigned long previous_time = 0; bool ecg[1]; const int ecgPin = 7; int beats = 0; int HR; unsigned long current_time; void setup() { Serial.begin(9600); } void loop() { current_time = millis(); while(current_time - previous_time < 10000) { ecg[0] = digitalRead(ecgPin); ecg[1] = digitalRead(ecgPin); Serial.print(current_time); Serial.print(" "); Serial.print(previous_time); Serial.println(" "); if(ecg[1] == 1 && ecg[0] == 0) { beats = beats + 1; } } HR = beats*6; Serial.print("Your Heart Rate is : "); Serial.print(HR); Serial.println(" bpm"); beats = 0; previous_time = current_time; } [Screenshot (182)]

[image] m7mman: while(current_time - previous_time 1000?

Thank you. I thought it updates even after entering the while loop. I solved it by introducing the millis function inside the while loop.

bool ecg[1]; An array with only one element What use is that ? ecg[0] = digitalRead(ecgPin); ecg[1] = digitalRead(ecgPin); //NOTE that this element of the array does not exist if (ecg[1] == 1 && ecg[0] == 0) What are the chances of the two values being different ?

We are connecting the output of the ecg circuit to a comparator circuit that will output either 1 or 0 depending on the ECG value. We set the threshold to a point where only the R peaks are outputting 1. Results are looking good.

What is the frequency of the ECG signals ? Reading the state of an input twice within a few microseconds is likely to return the same value unless the frequency is very high Did you fix the problem with the number of elements in the ecg array or are you still writing to memory outside of it ? Please post a schematic of your project

[image] m7mman: I solved it by introducing the millis function inside the while loop. so you want to repeatedly make measurements as fast as possible for one second since your code seems to measuring heartbeat, why not measure the time time between beats, do some averaging and report?

consider following using button being pressed to simulate heartbeat corrected (i.e. unsigned long msecLst) const byte PinSensor = A1; unsigned long beatLst; unsigned long msecLst; float avg; byte inpLst; void loop (void) { unsigned long msec = millis(); byte inp = digitalRead (PinSensor); if (inpLst != inp) { inpLst = inp; if (LOW == inp) { if (0 == avg) avg = msec - beatLst; else avg += ((msec - beatLst) - avg) / 8; beatLst = msec; } } if (msec - msecLst >= 5000) { msecLst = msec; Serial.print (avg, 2); Serial.print (" "); Serial.println (60.0 / (avg / 1000)); } } void setup (void) { Serial.begin (9600); pinMode (PinSensor, INPUT_PULLUP); }

Why is the millis variable printing 0

Projects Programming

PerryBebbington May 8, 2023, 12:02pm 10

Not the best way to use millis().

if(current_time - previous_time > 10000)
Is better.

See Using millis() for timing. A beginners guide

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Why is the millis variable printing 0

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