BMA180 herky jerky transmission

Development Boards Arduino
1

Hi,

I’ve been trying to get a BMA180 (I’m on my second one already) to send a continuous stream of accel data via a serial port (eventually bluetooth but that’s a problem for a different day). I’ve looked at and tried to emulate numerous examples and consistently come across the problem of data coming in “fits and starts”. One packet, wait a second or two, a few more packets, etc etc. Usually this ends in the data stopping all together after 5, 10, 50 chunks.

My wiring is as show here : posting.php?mode=post&f=32 but I have VIO unconnected. When VIO is tied to 3.3V, my output is all 0’s.

This is my code, which is adapted from several other sources:

#include <Wire.h>
#define DEVICE ((byte)0x40)  
#define DATA_X0		0x02	
#define AXIS_SHIFT	2	
#define DELAY_RATE	500

int counter = 0;


static void readFrom(byte address, byte num, byte *buff) {
  Wire.beginTransmission(DEVICE); 
  Wire.write(address);      
  Wire.endTransmission(); 

  Wire.requestFrom(DEVICE, num);  
  num = Wire.available();

  while(num-- > 0) {
    *(buff++) = Wire.read(); // receive a byte
  }
}

void setup()
{
  Wire.begin();          // join i2c bus (address optional for master)
  Serial.begin(115200);  // start serial for output
  Serial.flush();
  delay(15);
}

void loop()
{
  digitalWrite(13, HIGH); 
  int axis[5] = {0x0101, 0, 0, 0, 0};
  readFrom(DATA_X0, 6, (byte*)(axis+1)); 
  
  axis[1] = axis[1] ;
  axis[2] = axis[2] ;
  axis[3] = axis[3] ;
  
  axis[4] = axis[1] + axis[2] + axis[3];
  Serial.println("");
  Serial.println(axis[1]);
  Serial.println(axis[2]);
  Serial.println(axis[3]);
  Serial.println(axis[4]);
  counter++;
  
  delay(100);              
  digitalWrite(13, LOW);  
  delay(100);             
}

This is what I get coming into the serial monitor, in weird sporadic thrusts:

-879
321
17077
16519

-411
345
16761
16695

249
0
0
249

…etc…

I suspect the 249 /0 /0/ 249 chunk is the temperature because it will go up and down a little although the application of my desk lamp caused all data to cease.

I am baffled. The ‘L’ LED on the arduino blinks when the packets get pushed out so I think it’s not a serial port problem. I would really appreciate any ideas here.

2

Hi kardasis,

I have been playing with the module recently (only using the I2C interface) and am having exactly the same problems with bursts of transmission. After trying numerous different settings for the sensor, I gave up trying to figure out what happened and set the bandwidth of the unit to 1200. I am polling for a high interrupt line every 10mS to give me 100Hz data rate. This is not a particularly neat way to do it but it appears to be working with intermittent readings having spurious data that will need to be filtered

Hopefully you have figured out what is happening because I don’t feel any closer to creating a fully working driver for the chip and from all the searches I have done online, nobody else appears to have either.

EvilCng