Update adxl355.ino

[petedl]

fixed sign extension from 20 to 32 bits and fixed multiple byte reads by putting chip select toggle in between reads

[rbp9802]

Hi Pete, i've been having some issues reading X an Z small accelerations, they tend to be the same when there are small movements. I test the same device on an python library and works well so i tried to copy what i think was making the issue. I'll just copy the code here.

I changed de readMultipleData function to a single multiple read instead of a multiple single read. It is faster and i pressume this was the issue because it set the CS pin HIGH after reading 1 byte maybe caussing trouble with the FIFO.

Original code:

void readMultipleData(int *addresses, int dataSize, int *readedData) {
  for(int i = 0; i < dataSize; i = i + 1) {
    digitalWrite(ADXL355_CS_PIN, LOW);  
    byte dataToSend = (addresses[i] << 1) | READ_BYTE;
    SPI1.transfer(dataToSend);
    readedData[i] = SPI1.transfer(0x00);
    digitalWrite(ADXL355_CS_PIN, HIGH);}
}

New code:

void readMultipleData(int addresses, int dataSize, int *readedData) {
  digitalWrite(ADXL355_CS_PIN, LOW);
  byte dataToSend = (addresses << 1) | READ_BYTE;
  SPI1.transfer(dataToSend);

  for(int i = 0; i < dataSize; i++) {
    readedData[i] = SPI1.transfer(0x00);}

  digitalWrite(ADXL355_CS_PIN, HIGH);
}

So you 9 registers from the first register XDATA3 = 0x09. Note that the original code started reading from the third register XDATA1 = 0x0A so you have to change axisMeasures index when calculating xdata, ydata and zdata as you read registers from MSB to LSB.

void ADXL355_get3V(){
  int Address = XDATA3;
  int axisMeasures[] = {0, 0, 0, 0, 0, 0, 0, 0, 0};
  int dataSize = 9;

  // Read accelerometer data
  readMultipleData(Address, dataSize, axisMeasures);

  // Split data
  xdata = (axisMeasures[2] >> 4) + (axisMeasures[1] << 4) + (axisMeasures[0] << 12);
  ydata = (axisMeasures[5] >> 4) + (axisMeasures[4] << 4) + (axisMeasures[3] << 12);
  zdata = (axisMeasures[8] >> 4) + (axisMeasures[7] << 4) + (axisMeasures[6] << 12);
  //                    ^                        ^                        ^     change index
  
  // extend the sign bit from bit 19 to bit 31
  xdata = ((xdata<<12)>>12);
  ydata = ((ydata<<12)>>12); 
  zdata = ((zdata<<12)>>12); 
}

you can also do functions like:

int ADXL355_getZ(){
  int axisAddresses = ZDATA3;
  int axisMeasures[] = {0, 0, 0};
  int dataSize = 3;

  readMultipleData(axisAddresses, dataSize, axisMeasures); // Read accelerometer data
  int zdata = (axisMeasures[2] >> 4) + (axisMeasures[1] << 4) + (axisMeasures[1] << 12); // Split data
  
  zdata = ((zdata<<12)>>12);  // extend the sign bit from bit 19 to bit 31
  return zdata;
}