Sidestep one second log rate with NeoGPS when another sensor on the board need to log faster

Question

The sample rate of an accelerometer, like an MPU6050, is much faster than the GPS log rate, different technology, different issues. A common GPS Reciver has, approximatly, one second log rate. In my specific case the accelerometer has a 100hz log rate.

With a previous code the gps log rate was slowing down the accelerometer log rate so i thought to introduce two counters:

• one for the gps
• one for the accelerometer

What i tried to do was:

  if ((lastLogGPS + LOG_RATE_GPS) <= micros()) {
  //Log accelerometer and gps data
  } else ((  if ((lastLog + LOG_RATE) <= micros()) {
  //Log only Accelerometer data
  }

---

1. Is that a speed and memory efficient solution? Or better way exist*?

2. During a 60 seconds test the board return me only the accelerometer value, never the satellites informations, i think there are some dumb errors in my code

---

Thanks for your help :)

This is the void loop section

void loop()
  {
    Wire.beginTransmission(MPU);
    Wire.write(0x3B);  // starting with register 0x3B (ACCEL_XOUT_H)
    Wire.endTransmission(false);
    Wire.requestFrom(MPU,14,true);   // request a total of 14 registers
    AcX=Wire.read()<<8;
    AcX|= Wire.read(); // 0x3B (ACCEL_XOUT_H) & 0x3C (ACCEL_XOUT_L)     
    AcY=Wire.read()<<8;
    AcY|=Wire.read();  // 0x3D (ACCEL_YOUT_H) & 0x3E (ACCEL_YOUT_L)
    AcZ=Wire.read()<<8;
    AcZ|=Wire.read();  // 0x3F (ACCEL_ZOUT_H) & 0x40 (ACCEL_ZOUT_L)
    GyX=Wire.read()<<8;
    GyX|=Wire.read();  // 0x43 (GYRO_XOUT_H) & 0x44 (GYRO_XOUT_L)
    GyY=Wire.read()<<8 ;
    GyY|=Wire.read();  // 0x45 (GYRO_YOUT_H) & 0x46 (GYRO_YOUT_L)
    GyZ=Wire.read()<<8;
    GyZ|=Wire.read();  // 0x47 (GYRO_ZOUT_H) & 0x48 (GYRO_ZOUT_L)
    if ((lastLogGPS + LOG_RATE_GPS) <= micros()) {
    while (gps.available( gpsPort )) {
    fix = gps.read();  // get the entire fix structure, once per second

    if (logGPSData()) { // Log the GPS data
    SerialMonitor.println( F("GPS logged.") ); // Print a debug message
    } else {// If we failed to log GPS
    // Print an error, don't update lastLog
    SerialMonitor.println( F("Failed to log new GPS data.") );
      }
    }
   lastLogGPS=micros();
  }
  else{ 
    if ((lastLog + LOG_RATE) <= micros()) {

      printImuData(dataFile,lastLog, AcX, AcY, AcZ, GyX, GyY, GyZ);
      dataFile.flush(); 
      }
    lastLog=micros(); 
    }
  } 

This the function that print only the accelerometer informations:

static void printImuData(Print &printer, unsigned long lastLog,
        int16_t AcX, int16_t AcY, int16_t AcZ,
        int16_t GyX, int16_t GyY, int16_t GyZ)
{//Printing the mpu6050 information 

  printer.print("0");   printer.print(",");   //0 longitude
  printer.print("0");   printer.print(",");   //0 latitude
  printer.print("0");   printer.print(",");   //0 altitude
  printer.print("0");   printer.print(",");   //0 speed
  printer.print("0");   printer.print(",");   //0 course
  printer.print("0");   printer.print(",");   //0 date
  printer.print("0");   printer.print(",");   //0 time 
  printer.print("0");   printer.print(",");   //0 satellites
  printer.print(lastLog); printer.print(",");   
  printer.print(AcX);     printer.print(",");
  printer.print(AcY);     printer.print(",");
  printer.print(AcZ);     printer.print(",");
  printer.print(GyX);     printer.print(",");
  printer.print(GyY);     printer.print(",");        
  printer.println(GyZ);  

}

And this is the part for the GPS informations:

byte logGPSData()
{
  if (dataFile.isOpen())
  { // Print longitude, latitude, altitude (in feet), speed (in mph), course
    // in (degrees), date, time, and number of satellites.

    if (fix.valid.location)
      dataFile.print(fix.longitude(), 6);
    dataFile.print(',');
    if (fix.valid.location)
      dataFile.print(fix.latitude(), 6);
    dataFile.print(',');
    if (fix.valid.altitude)
      dataFile.print(fix.altitude() * 3.2808, 1);
    dataFile.print(',');
    if (fix.valid.speed)
      dataFile.print(fix.speed_mph(), 1);
    dataFile.print(',');
    if (fix.valid.heading)
      dataFile.print(fix.heading(), 1);
    dataFile.print(',');

    if (fix.valid.date) {
      dataFile.print( fix.dateTime.full_year() );
      if (fix.dateTime.month < 10)
        dataFile.print( '0' );
      dataFile.print( fix.dateTime.month );
      if (fix.dateTime.date < 10)
        dataFile.print( '0' );
      dataFile.print( fix.dateTime.date );
    }
    dataFile.print(',');

    if (fix.valid.time) {
      if (fix.dateTime.hours < 10)
        dataFile.print( '0' );
      dataFile.print( fix.dateTime.hours );
      if (fix.dateTime.minutes < 10)
        dataFile.print( '0' );
      dataFile.print( fix.dateTime.minutes );
      if (fix.dateTime.seconds < 10)
        dataFile.print( '0' );
      dataFile.print( fix.dateTime.seconds );
    }
    dataFile.print(',');

    if (fix.valid.satellites)
      dataFile.print(fix.satellites);
  dataFile.print(',');  
  dataFile.print(lastLogGPS);  
    dataFile.print(',');
    dataFile.print(AcX);
    dataFile.print(',');
    dataFile.print(AcY);
    dataFile.print(',');
    dataFile.print(AcZ);
    dataFile.print(',');
    dataFile.print(GyX);
    dataFile.print(',');
    dataFile.print(GyY);
    dataFile.print(',');
    dataFile.print(GyZ);

    dataFile.println();
    dataFile.flush(); // make sure the file contains at least this much

    return 1; // Return success
  }

  return 0; // If we failed to open the file, return fail
}

Here a pic of some data returned by Arduino

*I need to load easily the *.csv whith the recorded data on matlab so i have some constraints.

Answer 1

Ok, I won't recreate your whole code, but here is a logic snippet that you can use.

Let's suppose that you have 2 sensors, sensor1 and sensor2.

sensor1 is read every 10 milliseconds and sensor2 is read every 16 milliseconds.

Here is what you would do:

Make 2 global variables for your timers :

unsigned long timer1 = 0;
unsigned long timer2 = 0;

Then make 2 constants for the frequency, this example will set the frequency in milliseconds.

const int frequency1 = 10;
cosnt int frequency2 = 16;

Then in your void loop, you would do something like this:

void loop () {
    if (timer1 + frequency1 >= millis()
        read(sensor1);
        timer1 = millis();
    }

    if (timer2 + frequency2 >= millis()
        read(sensor2);
        timer2 = millis();
    }
}

This method makes sure that your code isn't going to get stuck anywhere. I would also suggest to remove any while loops because of that danger that it might freeze& your code.