Help, please!

Hi,
I need your help.

I want to write a program for my Arduino but I am facing a situation.

I bought a SD shield which is working with my SD card using programs in the Arduino software.

I have 2 signals, a source signal and a received signal. I am doing a comparaison of the first signal with a value I fixed, then I save the time at which this event approximately occured, Then if my received signal respect a second condition, I take the difference between the two moments those events happened and I want to save that difference in a txt document on a SD card, the fact.

I've seen on Google that saving a file took time so I created a condition on the total saving of the file but with or without it my program does'not work meaning that my SD has not data on it when I connect it to my computer.

Thank you for your help.

I hope to have been the most understandable.

This is my code :

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

int sonarPin = A3;
int sourcePin = A1;
unsigned long time;

int valSource = 0;
int valSonar = 0;
float valDepassementSonar = 1.2;
float valDepassementSource = 3.6;
float timeSource = 0;
float timeSonar = 0;
float timetot = 0;
int i = 0;

File myFile;

void setup() {
Serial.begin(9600);
Serial.print("Initializing SD card...");
if (!SD.begin(10)) {
Serial.println("initialization failed!");
while (1);
}
Serial.println("initialization done.");
}

void loop() {
if (10000000>=itimeSource){
myFile.close();
myFile = SD.open("sonardate.txt", FILE_WRITE);
i = i+1;
}
valSource = analogRead(sourcePin);
valSonar = analogRead(sonarPin);
if (valSource>=valDepassementSource
204.6) {
timeSource = micros();
if (valSonar>=valDepassementSonar*204.6) {
timeSonar = micros();
timetot = timeSonar - timeSource;
myFile.println(timetot);
}
}
Serial.println(timeSonar-timeSource);
}

Programme_Arduino.ino (1.13 KB)

You should post your code using code tags.

Have you tried printing to the serial console when you write to the SD card? I suspect you are never meeting the conditions to enter the code block that writes to the SD card.