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Merge pull request #44 from Aryan-Prakhar/main
Added some important updates to Heart Rate detection
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software/Faster_HeartRateDetection/Faster_HeartRateDetection.ino
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| // Faster_HeartRateDetection - BioAmp EXG Pill | ||
| // https://github.com/upsidedownlabs/BioAmp-EXG-Pill | ||
| // https://github.com/upsidedownlabs/Heart-BioAmp-Arduino-Firmware | ||
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| // Upside Down Labs invests time and resources providing this open source code, | ||
| // please support Upside Down Labs and open-source hardware by purchasing | ||
| // products from Upside Down Labs! | ||
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| // Copyright (c) 2021 - 2024 Upside Down Labs - contact [at] upsidedownlabs.tech | ||
| // Copyright (c) 2021 - 2024 Aryan Prakhar - aryanprakhar1010 [at] gmail.com | ||
| // Copyright (c) 2021 - 2024 Dev Saran Sujan - devsaransujan [at] gmail.com | ||
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| // Permission is hereby granted, free of charge, to any person obtaining a copy | ||
| // of this software and associated documentation files (the "Software"), to deal | ||
| // in the Software without restriction, including without limitation the rights | ||
| // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
| // copies of the Software, and to permit persons to whom the Software is | ||
| // furnished to do so, subject to the following conditions: | ||
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| // The above copyright notice and this permission notice shall be included in all | ||
| // copies or substantial portions of the Software. | ||
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| // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
| // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
| // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
| // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
| // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | ||
| // SOFTWARE. | ||
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| #include <math.h> | ||
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| // Define constants | ||
| #define SAMPLE_RATE 125 // Sampling rate in Hz | ||
| #define BAUD_RATE 115200 // Serial communication baud rate | ||
| #define INPUT_PIN A2 // Analog pin for ECG signal | ||
| #define OUTPUT_PIN 13 // Digital output pin for LED | ||
| #define DATA_LENGTH 26 // Length of data buffer for peak detection | ||
| #define buffer_size 5 // Size of circular arrays for BPM calculation | ||
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| // Global variables for BPM calculation | ||
| int data_index = 0; | ||
| uint32_t tdiff = 0; // Time difference between consecutive peaks | ||
| uint8_t bpm = 0; // Calculated Beats Per Minute | ||
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| // Circular arrays for BPM calculation | ||
| int timeBuffer_index = -1; | ||
| int sumBuffer_index = -1; | ||
| uint32_t timeBuffer[buffer_size] = {0}; | ||
| uint32_t sumBuffer[buffer_size] = {0}; | ||
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| // Variables for BPM calculation | ||
| uint32_t previous_time = 0; | ||
| uint32_t sum = 0; | ||
| uint32_t average = 0; | ||
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| // Variables for peak detection and debouncing | ||
| unsigned long lastPeakStartTime = 0; | ||
| unsigned long peakCooldownPeriod = 2; // Cooldown period in milliseconds | ||
| bool isPeakActive = false; | ||
| bool peakEvent = false; | ||
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| void setup() { | ||
| // Initialize serial communication | ||
| Serial.begin(BAUD_RATE); | ||
| // Set pin modes | ||
| pinMode(INPUT_PIN, INPUT); | ||
| pinMode(OUTPUT_PIN, OUTPUT); | ||
| } | ||
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| void loop() { | ||
| // Calculate elapsed time since last loop | ||
| static unsigned long past = 0; | ||
| unsigned long present = micros(); | ||
| unsigned long interval = present - past; | ||
| past = present; | ||
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| // Timer for maintaining consistent sampling rate | ||
| static long timer = 0; | ||
| timer -= interval; | ||
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| // Sample and process ECG signal at specified rate | ||
| if(timer < 0){ | ||
| timer += 1000000 / SAMPLE_RATE; | ||
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| // Read sensor value and normalize | ||
| float sensor_value = analogRead(INPUT_PIN); | ||
| float signal = ECGFilter(sensor_value)/512; | ||
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| // Detect peaks in the signal | ||
| peakEvent = Getpeak(signal); | ||
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| // Blink LED on detected peak | ||
| digitalWrite(OUTPUT_PIN, peakEvent); | ||
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| // Calculate BPM when a peak is detected | ||
| if(peakEvent){ | ||
| // Update time buffer for peak timing | ||
| if(timeBuffer_index == -1){ | ||
| timeBuffer_index = (timeBuffer_index + 1) % buffer_size; | ||
| timeBuffer[timeBuffer_index] = micros(); | ||
| } | ||
| else{ | ||
| previous_time = timeBuffer[timeBuffer_index]; | ||
| timeBuffer_index = (timeBuffer_index + 1) % buffer_size; | ||
| timeBuffer[timeBuffer_index] = micros(); | ||
| tdiff = timeBuffer[timeBuffer_index] - previous_time; | ||
| } | ||
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| // Calculate BPM using circular arrays | ||
| if(sumBuffer_index == -1){ | ||
| sumBuffer_index = (sumBuffer_index + 1) % buffer_size; | ||
| } | ||
| else{ | ||
| if(sumBuffer[sumBuffer_index] == 0){ | ||
| sumBuffer[sumBuffer_index] = tdiff; | ||
| sum = sum + sumBuffer[sumBuffer_index]; | ||
| sumBuffer_index = (sumBuffer_index + 1) % buffer_size; | ||
| } | ||
| else{ | ||
| sum = sum - sumBuffer[sumBuffer_index]; | ||
| sumBuffer[sumBuffer_index] = tdiff; | ||
| sum = sum + sumBuffer[sumBuffer_index]; | ||
| sumBuffer_index = (sumBuffer_index + 1) % buffer_size; | ||
| average = sum / buffer_size; | ||
| bpm = (60 * 1000000) / average; | ||
| Serial.print("BPM : "); | ||
| Serial.println(bpm); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| // Function to detect peaks in the ECG signal | ||
| bool Getpeak(float new_sample) { | ||
| // DATA_LENGTH explanation: | ||
| // This constant defines the size of the sliding window used for peak detection. | ||
| // It determines how many recent samples are considered when calculating the mean | ||
| // and standard deviation of the signal. A larger value provides more stable | ||
| // detection but may introduce more lag. | ||
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| // Buffers for data, mean, and standard deviation | ||
| static float data_buffer[DATA_LENGTH]; | ||
| static float mean_buffer[DATA_LENGTH]; | ||
| static float standard_deviation_buffer[DATA_LENGTH]; | ||
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| // Check for peak | ||
| // A peak is detected if the new sample exceeds the mean by more than | ||
| // half the DATA_LENGTH times the standard deviation | ||
| bool rawPeak = false; | ||
| if (new_sample - mean_buffer[data_index] > (DATA_LENGTH/2) * standard_deviation_buffer[data_index]) { | ||
| data_buffer[data_index] = new_sample + data_buffer[data_index]; | ||
| rawPeak = true; | ||
| } else { | ||
| data_buffer[data_index] = new_sample; | ||
| rawPeak = false; | ||
| } | ||
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| // Event-based debounce logic | ||
| // This prevents multiple detections of the same peak by implementing a cooldown period | ||
| bool peakEvent = false; | ||
| unsigned long currentTime = micros(); | ||
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| if (rawPeak && !isPeakActive && (currentTime - lastPeakStartTime > peakCooldownPeriod)) { | ||
| // Start of a new peak | ||
| isPeakActive = true; | ||
| lastPeakStartTime = currentTime; | ||
| peakEvent = true; | ||
| } else if (!rawPeak && isPeakActive) { | ||
| // End of the current peak | ||
| isPeakActive = false; | ||
| } | ||
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| // Calculate mean of the data buffer | ||
| float sum = 0.0, mean, standard_deviation = 0.0; | ||
| for (int i = 0; i < DATA_LENGTH; ++i){ | ||
| sum += data_buffer[(data_index + i) % DATA_LENGTH]; | ||
| } | ||
| mean = sum / DATA_LENGTH; | ||
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| // Calculate standard deviation of the data buffer | ||
| for (int i = 0; i < DATA_LENGTH; ++i){ | ||
| standard_deviation += pow(data_buffer[(i) % DATA_LENGTH] - mean, 2); | ||
| } | ||
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| // Update mean buffer | ||
| mean_buffer[data_index] = mean; | ||
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| // Update standard deviation buffer | ||
| standard_deviation_buffer[data_index] = sqrt(standard_deviation / DATA_LENGTH); | ||
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| // Update data_index for circular buffer implementation | ||
| data_index = (data_index + 1) % DATA_LENGTH; | ||
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| // Return true if a peak event occurred, false otherwise | ||
| return peakEvent; | ||
| } | ||
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| // Band-Pass Butterworth IIR digital filter for ECG signal | ||
| // Sampling rate: 125.0 Hz, frequency range: [0.5, 44.5] Hz | ||
| // Filter is order 4, implemented as second-order sections (biquads) | ||
| // Reference: | ||
| // https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.butter.html | ||
| // https://courses.ideate.cmu.edu/16-223/f2020/Arduino/FilterDemos/filter_gen.py | ||
| float ECGFilter(float input) | ||
| { | ||
| float output = input; | ||
| { | ||
| static float z1, z2; // filter section state | ||
| float x = output - 0.70682283*z1 - 0.15621030*z2; | ||
| output = 0.28064917*x + 0.56129834*z1 + 0.28064917*z2; | ||
| z2 = z1; | ||
| z1 = x; | ||
| } | ||
| { | ||
| static float z1, z2; // filter section state | ||
| float x = output - 0.95028224*z1 - 0.54073140*z2; | ||
| output = 1.00000000*x + 2.00000000*z1 + 1.00000000*z2; | ||
| z2 = z1; | ||
| z1 = x; | ||
| } | ||
| { | ||
| static float z1, z2; // filter section state | ||
| float x = output - -1.95360385*z1 - 0.95423412*z2; | ||
| output = 1.00000000*x + -2.00000000*z1 + 1.00000000*z2; | ||
| z2 = z1; | ||
| z1 = x; | ||
| } | ||
| { | ||
| static float z1, z2; // filter section state | ||
| float x = output - -1.98048558*z1 - 0.98111344*z2; | ||
| output = 1.00000000*x + -2.00000000*z1 + 1.00000000*z2; | ||
| z2 = z1; | ||
| z1 = x; | ||
| } | ||
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| return output; | ||
| } |
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