Java • Re: Java and ADXL345 accelerometer

Code:

// This java file can be used to collect data from an ADXL345 accelerometer on Rapberry Pi// not discussed here - connecting device to Pi, setting up i2c connection// Recommend installing Frank Delporte's Pi4J template - this java file was used with it// see Frank DelPorte git hub to dload a template for creating a pi4j application - follow his instructions// google 'adxl345 data sheet', and study the adxl345 data sheet // code below sets values in three key registers of the adxl345 device: 0x2C, 0x2D, 0x31 to set up the device// Writing to Register 0x31 sets format of data coming from the accelerometer// - bits D3,D1, and D0 are used to set the format - D3 sets resolution 1000 = high res, 0000 = low res// - bits D1 and D0 set max g value: 00= +/- 2g, 01= +/- 4g, 10 = +/- 8g, 11 = +/- 16 g// - ex: 1011 = decimal 11 (8+0+2+1)= hex 0x0B is high resolution and +/- 16g - used in code below (write to register 0x31)// - in hi res, values received are 13 bit. in low res: 10bit for 2g, 11bit for 4g, 12bit for 8g, 13 bit for 16g// code below reads values from 0x32-0x37 to collect acceleration data for three axes// the data comes in 6 bytes, 2 bytes for each axis, the two bytes for each axis must be combined to get accel value for that axis// ---- data manipulation:// values are received as as 16 bit (two bytes) "twos complement" for each axis// twos complement breaks the measured value into two parts. one byte for the leftmost 8 bits, one byte for the right 8 bits       // the more significant byte must moved to the left by 8 bits, then added to the less signif byte to reconstruct the measured value// this can be done with a bit shift <<8 (move the byte left 8 bits into the position of higher values) or by multiplying it by 256// &0x1F in code below is a 'bitwise AND' that will cause only 5 right bits of this byte to be used (0x1f=00011111) -google 'bitwise AND'// &0x1F keeps only 5 rightmost bits- appropriate for this example using a 13 bit value (full res, 16g). use different & 0xXX for different bit length// ---- dealing with signed values:// Since this a 13 bit value, max positive value is 0111111111111=4095. (13th bit is reserved, if 1 it would say value is negative)// The 13th bit = 4096, if total value is above 4095, the value needs to be processed as a negative number// If statement determines whether the data value implies a 1 in the 13th bit, if true converts it to a negative value// 4095 and 8192 below are appropriate for a 13 bit value (12, 11, 10 bit values need diff numbers here)// - bit size of received data determines proper AND mask, and negative value check// - 10 bit &03 with if >511, accel-=1024; 11 bit &07 with if >1023, accel-=2048; 12bit &0F with if >2047, accel-=4096 // ---- Printing results to file// this java file will print the results to a csv file if not desired delete or comment out where shown

Code:

import com.pi4j.Pi4J;import com.pi4j.context.Context;import com.pi4j.io.i2c.I2C;import com.pi4j.io.i2c.I2CConfig;import com.pi4j.io.i2c.I2CProvider;import java.io.File;import java.io.FileWriter;import java.util.Calendar; import java.text.SimpleDateFormat ;public class Ocala{ public static void main(String args[]) throws Exception{ boolean firstPass = true ;SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yy hh:mm:ss") ;     int busid = 1 ;            int i2cAddress = 0x53 ;  // address for adxl345     Context pi4j = Pi4J.newAutoContext();    I2CProvider i2cProvider = pi4j.provider("linuxfs-i2c");    I2CConfig i2CConfig = com.pi4j.io.i2c.I2C.newConfigBuilder(pi4j).id(busid+": device "+i2cAddress).bus(busid).device(i2cAddress).build();        try {       I2C device = i2cProvider.create(i2CConfig);       device.writeRegister(0x2C, (byte)0x0A);  // 0x2C is register address for data rate 0x0A is default 100 Hz                device.writeRegister(0x2D, (byte)0x08);  // 0x2D is register address for power control, bit D3 = value of 8 = 'turn on  measurement'       device.writeRegister(0x31, (byte)0x0B);  // 0x31 is register address for data format, here full res 16g - see header                                                       while (true) {//----    following write to file - don't remove sleep      File fil = new File("javadata.csv") ;      FileWriter filWrit = new FileWriter(fil, true) ;      if (firstPass){     String printString = "---------- New Java Run ----------\n" ;     filWrit.append(printString);     firstPass = false ;      }  //  if firstpass        Thread.sleep(250);      //---- ADXL345 datasheet recomends reading all 6 bytes at same time for data consistency              byte[] data = new byte[6];         data[0] = (byte)device.readRegister(0x32);        data[1] = (byte)device.readRegister(0x33);       data[2] = (byte)device.readRegister(0x34);       data[3] = (byte)device.readRegister(0x35);       data[4] = (byte)device.readRegister(0x36);       data[5] = (byte)device.readRegister(0x37); //---- special processing of the values received from the adxl345 is required before they can be used - see notes in header             int xAccl = ((data[1] & 0x1F) * 256 + (data[0]));        if(xAccl > 4095){          xAccl -= 8192;       }  //if xaccl       int yAccl = ((data[3] & 0x1F) * 256 + (data[2]));        if(yAccl > 4095){          yAccl -= 8192;       }  //if yaccl       int zAccl = ((data[5] & 0x1F) * 256 + (data[4]));        if(zAccl > 4095){          zAccl -= 8192;       }  //if zaccl       System.out.printf("X: %d Y: %d Z: %d %n   ", xAccl, yAccl, zAccl);//---- following statements write to file - don't remove closing brace               Calendar cal = Calendar.getInstance() ;       filWrit.append(sdf.format(cal.getTime())) ;       filWrit.append(", ");       filWrit.append(String.valueOf(xAccl));       filWrit.append(", ");       filWrit.append(String.valueOf(yAccl));       filWrit.append(", " );       filWrit.append(String.valueOf(zAccl));         filWrit.append("\r\n");      filWrit.flush() ;      filWrit.close() ;                } // while           }catch(Exception e){    System.out.printf("some stupid error by jd");    } // catch }    // main}     // class