Hi,
I'm working with an Arduino mega 2560 and ADXL345. The sampling frequency I need is 200Hz.I tried changing the baud rate and delay but in every second, the number of data collected per second deceases.
How do I program Arduino to satisfy that frequency?
Thanks
Welcome to the Forum. Please read these two posts:
How to use this forum - please read. and
Read this before posting a programming question ...
We have no idea how to solve your problem because we can't see it. Please post your code using code tags. The code tags make the code look
like this
when posting source code files. It makes it easier to read, and can be copied with a single mouse click. Also, if you don't do it, some of the character sequences in the code can be misinterpreted by the forum code as italics or funny emoticons.
Unless the sketch is too large, it's better if you post your code, rather than attach it. When it's attached, we have to download it, create a folder then open your code in our IDE. And afterwards, the folder remains unless we navigate to the "Temp" folder and manually remove it. It's much easier to just view the code in your post.
This is not really my code. I downloaded the PDE file from a website and played around with the baud rate and delay().
code downloaded from hotmcu.com
#include <Wire.h>
#define Register_ID 0
#define Register_2D 0x2D
#define Register_X0 0x32
#define Register_X1 0x33
#define Register_Y0 0x34
#define Register_Y1 0x35
#define Register_Z0 0x36
#define Register_Z1 0x37
int ADXAddress = 0xA7 >> 1; // the default 7-bit slave address
int reading = 0;
int val=0;
int X0,X1,X_out;
int Y0,Y1,Y_out;
int Z1,Z0,Z_out;
double Xg,Yg,Zg;
void setup()
{
Wire.begin();
Serial.begin(115200);
delay(100);
// enable to measute g data
Wire.beginTransmission(ADXAddress);
Wire.write(Register_2D);
Wire.write(8); //measuring enable
Wire.endTransmission(); // stop transmitting
}
void loop()
{
//--------------X
Wire.beginTransmission(ADXAddress); // transmit to device
Wire.write(Register_X0);
Wire.write(Register_X1);
Wire.endTransmission();
Wire.requestFrom(ADXAddress,2);
if(Wire.available()<=2)
{
X0 = Wire.read();
X1 = Wire.read();
X1=X1<<8;
X_out=X0+X1;
}
//------------------Y
Wire.beginTransmission(ADXAddress); // transmit to device
Wire.write(Register_Y0);
Wire.write(Register_Y1);
Wire.endTransmission();
Wire.requestFrom(ADXAddress,2);
if(Wire.available()<=2)
{
Y0 = Wire.read();
Y1 = Wire.read();
Y1=Y1<<8;
Y_out=Y0+Y1;
}
//------------------Z
Wire.beginTransmission(ADXAddress); // transmit to device
Wire.write(Register_Z0);
Wire.write(Register_Z1);
Wire.endTransmission();
Wire.requestFrom(ADXAddress,2);
if(Wire.available()<=2)
{
Z0 = Wire.read();
Z1 = Wire.read();
Z1=Z1<<8;
Z_out=Z0+Z1;
}
//
Xg=X_out/256.0;
Yg=Y_out/256.0;
Zg=Z_out/256.0;
Serial.print("X= ");
Serial.print(Xg);
Serial.print(" ");
Serial.print("Y= ");
Serial.print(Yg);
Serial.print(" ");
Serial.print("Z= ");
Serial.print(Zg);
Serial.println(" ");
delay(5);
}
Sorry, I am not familiar with the Wire library.
...R
@Robin2. It's okay. Thanks anyway. 
I think you are trying to use "delay(5);" to get 200Hz.
Use millis() or micros() instead to get more consistent timing, since the timing of the loop may change each time.
Somehing like:
unsigned long previousMillis = 0;
const byte period_ms = 5;
void loop()
{
unsigned long currentMillis = millis();
if (currentMillis - previousMillis >= period_ms)
{
previousMillis = currentMillis;
//--------------X
Wire.beginTransmission(ADXAddress); // transmit to device
...
}