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Problems with accelerometer MMA7455L

 
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nOgUkO
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Problems with accelerometer MMA7455L
PostPosted: Tue Apr 28, 2009 2:59 am     Reply with quote
Hi Guys!

I´m using the accelerometer of freescale MMA7455L via I2C.
The microcontroller that i´m using is the PIC18LF4553 runing at 3.3V

I have some problems when i try reading the registers 0x06 0x07 0x08 (8 bit value of x y and z axis); the data displayed in my LCD varies constantly: sometimes read 245, 231, 255, 1, 0, 10, 7... random values

There is the code:

Code:


#include <18F4553.h>
#fusesXTPLL,NOWDT,NOPROTECT,NOLVP,NODEBUG,PLL1,CPUDIV1,USBDV,NOVREGEN

#use delay(clock=48000000)
#define USB_CON_SENSE_PIN PIN_C0
#include <usb_cdc.h>
#include <lcd.c>
#use i2c(master,slow,sda=PIN_B0, scl=PIN_B1,FORCE_HW)
 
int data=0;




void main() {
delay_ms(100);
lcd_init();


i2c_start();
i2c_write(0x3A); //0x1D shifted in with a 0 had been 0x3A
i2c_write(0x16); //MODE CONTROL REGISTER
i2c_write(0x05); //CONTINOUS MEASUREMENT
i2c_stop();
delay_ms(30); 


loop:
i2c_start();
i2c_write(0x3A);
i2c_write(0x08); //8 bits output value Z
i2c_start();
i2c_write(0x3B); //0x1D shifted in with a 1 had been 0x3B
data=i2c_read(0);
i2c_stop();
delay_ms(500);
printf(lcd_putc,"\f %u",data);//PRINT DATA INTO LCD

goto loop;
 
}




Someting is wrong in my code?

Please help me!

Thanks! Wink
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Tue Apr 28, 2009 3:48 am     Reply with quote
If readback of configuration registers is correct (constant), it's most likely sensor noise. The values you gave, are at least in an allowed range for zero readings.
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