Accelerometer and measure times

Other Hardware Science and Measurement
1

Hi group!
I am using arduino for a school project, where I want to measure accelerations, or vibrations and save them on an SD card. What I need is that I set the sampling time, because it gives me a lot of variation when I graph it later, I leave the code, to see if they can see anything ..

#include <SD.h>
#include <SPI.h>

#include <AcceleroMMA7361.h>\

AcceleroMMA7361 accelero;
int x;
int y;
int z;
volatile unsigned MuestreoAnterior = 0;
volatile unsigned MuestreoActual = 0;
volatile unsigned deltaMuestreo = 0;
const int chipSelect = 4;

void setup()
{
Serial.begin(9600); // Preparar las comunicaciones serie para mostrar mensajes en la consola
accelero.begin(13, 12, 11, 10, A0, A1, A2);
accelero.setARefVoltage(3.3); //sets the AREF voltage to 3.3V
accelero.setSensitivity(LOW); //sets the sensitivity to +/-6G
accelero.calibrate();

while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}

Serial.print("Initializing SD card...");

// see if the card is present and can be initialized:
if (!SD.begin(chipSelect)) {
Serial.println("Card failed, or not present");
// don't do anything more:
while (1);
}
Serial.println("card initialized.");
}
void loop()
{
MuestreoActual = millis();
deltaMuestreo = (double) MuestreoActual - MuestreoAnterior;
if (deltaMuestreo<=60);

x = accelero.getXAccel();
y = accelero.getYAccel();
z = accelero.getZAccel();
Serial.print("\nx: ");
Serial.print(x);
Serial.print(" \ty: ");
Serial.print(y);
Serial.print(" \tz: ");
Serial.print(z);
Serial.print("\tG*10^-2");
delay(10);

String dataString = "";

// read three sensors and append to the string:
dataString += String(MuestreoActual);
dataString += ",";
dataString += String(x);
dataString += ",";
dataString += String(y);
dataString += ",";
dataString += String(z);
dataString += ";";

// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
File dataFile = SD.open("datalog.txt", FILE_WRITE);

// if the file is available, write to it:
if (dataFile) {
dataFile.println(dataString);
dataFile.close();
// print to the serial port too:
Serial.println(dataString);
}
// if the file isn't open, pop up an error:
else {
Serial.println("error opening datalog.txt");
}

}//make it readable

thanks a lot

2

why don't you capture and save a timestamp (e.g. micros()) along with your data. plot data with respect to the timestamp not assuming equal periods

3

Learn how to correctly use millis() for timing.
Non-blocking timing tutorials:
Several things at a time.
Beginner's guide to millis().
Blink without delay().

Are you aware of the pitfalls of using the String class with Arduino?