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ADXL375Z Shock Threshold False Triggering

Category: Hardware
Product Number: ADXL375

Hello, 

I am working on ADXL375 and interfacing it with Arduino UNO using I2C protocol. I get the values of X, Y, Z axis as mentioned in the datasheet, i.e., when placed horizontally I get x=0g, y=0g, z=1g (approx. calibrated). I have enabled trigger mode and mapped interrupt to INT2. My Shock Threshold is set to 0x28 = 31.2g, and I am detecting for single shock event 

When I tap the module on table, interrupt triggers even though the threshold is 31.2g, but the values I get are unchanged (around x= 0, y=0, z=1). How to get the values of X, Y, Z during the shock? When I tilt the module, I can see the values change accordingly. but these values hardly go beyond 3g. what am I doing wrong?

Here is my code setup:

/*START Set Shock Threshold*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x1D); //Shock Duration Register Address
  Wire.write(0x28); //Scale Factor is 780mg/LSB, hence 0x28 = 31.2g
  Wire.endTransmission();
  /*END Set Shock Threshold*/

  /*START Set DUR Thresh_SHOCK*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x21); //Shock Duration Register Address
  Wire.write(0x50); //Scale Factor is 625us/LSB, hence 0x50 = 50ms
  Wire.endTransmission();
  /*END Set DUR Thresh_SHOCK*/

  /*START Set Latency*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x22); //Latent Register Address
  Wire.write(0x20); //Scale Factor is 1.25ms/LSB, hence 0x20 = 400ms
  Wire.endTransmission();
  /*END Set Latency*/

  /*START Set Shock Window to 300ms*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x23); //Window Register Address
  Wire.write(0xF0); //Scale Factor is 1.25ms/LSB, hence 0xF0 = 300ms
  Wire.endTransmission();
  /*END Set Shock Window to 300ms*/

  /*START Enable XYZ-Axis Shock Detection START*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x2A); //SHOCK_AXES Register
  Wire.write(0x07); //Enable SHOCK_X, SHOCK_Y, SHOCK_Z
  Wire.endTransmission();
  /*END Enable XYZ-Axis Shock Detection END*/

  /*START Set Out-Data-Rate(ODR) to 3200Hz*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x2C); //BW_RATE Register Address
  Wire.write(0x0F); //3200 Hz Output Data Rate
  Wire.endTransmission();
  /*END Set Out-Data-Rate(ODR) to 3200Hz */

  /*START Enable Single Shock Interrupt*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x2E); //INT_Enable Register Address
  Wire.write(0x40); //Enable Single Shock Int
  Wire.endTransmission();
  /*END Enable Single Shock Interrupt*/
 
  /*START Assign Single Shock Interrupt*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x2F); //INT_Map Register Address
  Wire.write(0x40); //Assign Single Shock Int
  Wire.endTransmission();
  /*END Assign Single Shock Interrupt*/  
  
  /*START Data Format*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x31); //DATA_FORMAT Reg
  Wire.write(0x0B); 
  Wire.endTransmission();
  /*END Data Format*/

  /*START Enable Trigger Mode*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x38); //FIFO_CTL Register Address
  Wire.write(0xEA); //Enable Trigger Mode, set samples = 10
  Wire.endTransmission();
  /*END Enable Trigger Mode*/

  /*START Offset Calibration*/
  // Scale Factor = 0.196g/MSB
  Wire.beginTransmission(Device_Address);
  Wire.write(0x1E); //OFSX Address
  Wire.write(0xFA); //OFSX offset 
  Wire.endTransmission();

  Wire.beginTransmission(Device_Address);
  Wire.write(0x1F); //OFSY Address
  Wire.write(0xFB); //OFSY offset
  Wire.endTransmission();

  Wire.beginTransmission(Device_Address);
  Wire.write(0x20); //OFSZ Address
  Wire.write(0xFF); //OFSZ offset
  Wire.endTransmission();
  /*END Offset Calibration*/

  /*Start Enable Measuring*/
  Wire.beginTransmission(Device_Address);
  Wire.write(0x2D); //POWER_CTL Register
  Wire.write(0x08); //Enable Measuring
  Wire.endTransmission();
  /*END Enable Measuring*/
  
  /*Attach Interrupt to Digital pin 2*/
  attachInterrupt(digitalPinToInterrupt(2), ISR_Func, RISING);

Here is how I am receiving the values:

int16_t data_x = 0, data_x_lsb = 0; 
int16_t data_y = 0, data_y_lsb = 0; 
int16_t data_z = 0, data_z_lsb = 0;

Wire.beginTransmission(Device_Address);
Wire.write(0x32); //read LSB
Wire.endTransmission();

    Wire.requestFrom(Device_Address, 6);   
    while (Wire.available()) {
      data_x_lsb = Wire.read();
      data_x = Wire.read();
      data_y_lsb = Wire.read();
      data_y = Wire.read();
      data_z_lsb = Wire.read();
      data_z = Wire.read();

       data_x = (data_x << 8) | (data_x_lsb);
       data_y = (data_y << 8) | (data_y_lsb);
       data_z = (data_z << 8) | (data_z_lsb);
    }
    
data_x = (double)data_x*49/1000
data_y = (double)data_y*49/1000
data_z = (double)data_z*49/1000

Sample output:

14:36:51.120 -> -0.072	-0.067	0.977
14:36:51.221 -> -0.087	-0.096	0.949
14:36:51.325 -> 0.010	-0.191	0.988
14:36:51.427 -> -0.062	-0.162	1.071
14:36:51.536 -> -0.010	-0.088	1.071
14:36:51.614 -> -0.015	-0.037	1.052
14:36:51.725 -> -0.022	-0.047	1.044
14:36:51.837 -> 0.062	-0.043	1.012
14:36:52.025 -> FIFO STATUS REG: A0
14:36:52.025 -> Shock Occured
14:36:52.062 -> ACT STATUS SHOCK REG: 1
14:36:52.062 -> INT_SOURCE: C3
14:36:52.137 -> 0.055	-0.081	0.997
14:36:52.252 -> 0.024	0.031	1.033
14:36:52.354 -> 0.011	-0.072	1.079
14:36:52.455 -> 0.022	-0.031	0.973
14:36:52.547 -> 0.014	-0.042	1.041
14:36:52.654 -> -0.062	-0.036	1.018
14:36:52.770 -> -0.080	-0.003	1.003
14:36:52.880 -> -0.081	-0.118	1.084
14:36:52.972 -> -0.080	-0.039	1.046
14:36:53.079 -> -0.109	-0.016	0.930



edited code
[edited by: RajT at 1:29 PM (GMT -5) on 24 Jan 2023]