Hello! I am new here. I want to compute an average value by recording all readings for a specific time duration.
Logic in pseudo code:
/------------------------/
startTime=present;
ind=0;
do{
array[ind]=reading;
ind++;
timeDuration=present-startTime;
}while(timeDuration< desiredValue);
average=sum(array)/ind;
/----------------------/
Actual code:
#include "Wire.h"
#define numberOfElementForAve 50 // each reading will take about 2to3 milli seconds
#define aveTimeDuration 100 // the uplimit of time duration (in milli seconds) for computing average
// the above two constant has relationship, the rule of thumb is
// numberOfElementForAve*2 >=aveTimeDuration
// MPU6050 address
const int MPU_ADDR = 0x68;
// variables for holding data
int16_t aX;
int timeStart = 0, timeLoopStart, timeDuration, timeLoopDuration;
int16_t aveArr[numberOfElementForAve];
int aveCount;
void setup() {
//initialisation
Serial.begin(9600);
Wire.begin();
Wire.beginTransmission(MPU_ADDR); // Begins a transmission to the I2C slave (GY-521 board)
Wire.write(0x6B); // PWR_MGMT_1 register
Wire.write(0); // set to zero (wakes up the MPU-6050)
Wire.endTransmission(true);
}
void loop() {
aveCount = 0;
timeStart = millis();
// a loop for taking average readings
do {
timeLoopStart = millis();
Wire.beginTransmission(MPU_ADDR);
Wire.write(0x3B); // starting with register 0x3B (ACCEL_XOUT_H) [MPU-6000 and MPU-6050 Register Map and Descriptions Revision 4.2, p.40]
Wire.endTransmission(false); // the parameter indicates that the Arduino will send a restart. As a result, the connection is kept active.
Wire.requestFrom(MPU_ADDR, 7 * 2, true); // request a total of 7*2=14 registers
// take readings from MPU6050
aX = Wire.read() << 8 | Wire.read(); // reading registers: 0x3B (ACCEL_XOUT_H) and 0x3C (ACCEL_XOUT_L)
aveArr[aveCount] = aX;
aveCount++;
timeDuration = millis() - timeStart;
timeLoopDuration = millis() - timeLoopStart;
Serial.print("|| timeLoopDuration: ");
Serial.print(timeLoopDuration);
Serial.print("|| timeDuration: ");
Serial.println(timeDuration);
} while (timeDuration < aveTimeDuration);
delay(1000);
}
However, the time duration for each loop becomes (approximately)
1st loop: 2ms
2ns loop: 2ms
3rd loop: 20ms
4th loop: 45ms
nth loop: 45ms
I wonder what makes the 3rd and rests loops significantly slower than the first two. Is it possible to speed them to 2ms as well? Thanks in advance.
