RC Plane Mount for CFD Validation

#include "HX711-multi.h"

// Pins to the load cell amp
#define CLK A0      // clock pin to the load cell amp
#define DOUT1 A1    // data pin to the first lca
#define DOUT2 A2    // data pin to the second lca
#define DOUT3 A3    // data pin to the third lca

#define BOOT_MESSAGE "MIT_ML_SCALE V0.9"

#define TARE_TIMEOUT_SECONDS 4
#define TARE_DURATION_SECONDS 5  // Duration for averaging tare readings

byte DOUTS[3] = {DOUT1, DOUT2, DOUT3};

#define CHANNEL_COUNT sizeof(DOUTS)/sizeof(byte)

long int results[CHANNEL_COUNT];
long int tareOffsets[CHANNEL_COUNT] = {0};  // Stores tare offsets
float calibrationFactors[CHANNEL_COUNT] = {1.0, 1.0, 1.0};  // Stores calibration factors

HX711MULTI scales(CHANNEL_COUNT, DOUTS, CLK);

String inputString = ""; // To store incoming serial data
bool stringComplete = false; // Flag to indicate when a full message is received

void setup() {
  Serial.begin(115200);
  Serial.println(BOOT_MESSAGE);
  Serial.flush();
  pinMode(11, OUTPUT);
  
  tareWithAveraging();  // Perform tare with averaging at startup
}

void tareWithAveraging() {
  unsigned long startTime = millis();
  unsigned long duration = TARE_DURATION_SECONDS * 1000;
  
  long int sumReadings[CHANNEL_COUNT] = {0};
  int sampleCount = 0;

  // Collect readings for the specified duration
  while (millis() - startTime < duration) {
    scales.read(results); // Read raw data from load cells
    for (int i = 0; i < CHANNEL_COUNT; ++i) {
      sumReadings[i] += results[i];
    }
    sampleCount++;
    delay(10);  // Short delay to allow consistent sampling
  }

  // Calculate average readings and set as tare offsets
  for (int i = 0; i < CHANNEL_COUNT; ++i) {
    tareOffsets[i] = sumReadings[i] / sampleCount; // Average calculation
  }
}

void calibrateLoadCell(int cellIndex, float knownMass) {
  if (cellIndex < 0 || cellIndex >= CHANNEL_COUNT) {
    Serial.println("Invalid load cell index!");
    return;
  }

  Serial.println("Place the known mass on the load cell...");
  delay(5000); // Allow time to place the known mass
  
  scales.read(results); // Read raw data
  float rawValue = results[cellIndex] - tareOffsets[cellIndex]; // Apply tare offset
  calibrationFactors[cellIndex] = rawValue / knownMass; // Calculate calibration factor

  Serial.print("Calibration complete for load cell ");
  Serial.print(cellIndex);
  Serial.print(". Calibration factor: ");
  Serial.println(calibrationFactors[cellIndex]);
}

void sendCalibratedData() {
  scales.read(results); // Read raw data from load cells
  for (int i = 0; i < scales.get_count(); ++i) {
    long int calibratedValue = results[i] - tareOffsets[i];  // Apply tare offset
    float finalValue = calibratedValue / calibrationFactors[i]; // Apply calibration factor

    Serial.print(finalValue);  
    Serial.print((i != scales.get_count() - 1) ? "," : "\n"); // Use commas for separation, newline at the end
  }
  delay(10);
}


void serialEvent() {
  while (Serial.available()) {
    char inChar = (char)Serial.read();
    inputString += inChar;
    if (inChar == '\n') { // Check for end of message
      stringComplete = true;
    }
  }
}

void loop() {
  sendCalibratedData(); // Send calibrated data

  // Check if a complete message has been received
  if (stringComplete) {
    inputString.trim(); // Remove any leading/trailing whitespace
    if (inputString.startsWith("calibrate")) {
      int cellIndex = inputString.substring(10, 11).toInt(); // Extract load cell index
      float knownMass = inputString.substring(12).toFloat(); // Extract known mass
      calibrateLoadCell(cellIndex, knownMass); // Calibrate specified load cell
    } else if (inputString.equalsIgnoreCase("tare")) {
      tareWithAveraging();  // Re-tare using averaging
      Serial.println("System re-tared.");
    
    } else if (inputString.equalsIgnoreCase("constants")) {
      Serial.println("Calibration Constants:");
      Serial.print(calibrationFactors[0]);
      Serial.print(",");
      Serial.print(calibrationFactors[1]);
      Serial.print(",");
      Serial.println(calibrationFactors[2]);

      Serial.println("Tare Offsets:");
      Serial.print(tareOffsets[0]);
      Serial.print(",");
      Serial.print(tareOffsets[1]);
      Serial.print(",");
      Serial.println(tareOffsets[2]);      
      delay(5000);
    }
    inputString = ""; // Clear the input string
    stringComplete = false; // Reset the flag
  }
}