Mindsensors Pressure Sensor PPS58-Nx

[fussel_dlx]

Hello,

I'm currently trying to get the pressure sensor from mindsensors to work without success.

I tried to translate the NXC Classes from their download page to java:
http://www.mindsensors.com/index.php?mo ... ent_id=188

I have some basics in java and I got other sensors to work but I stuck with this thing.

Could someone help to just read the raw values?

many thanks

[skoehler]

You should probably post the code you're using right now to read the raw values. Maybe someone can spot the error.

[fussel_dlx]

This is my actual code with the c method in the comment:

Code: Select all

import lejos.nxt.I2CPort;
import lejos.nxt.I2CSensor;

public class PressureSensor extends I2CSensor {

   //Method in C:
   //unsigned int PPS_ReadValue(byte port, byte reg, byte count, byte addr) {
   //  unsigned int result = 0;
   //  byte outBuf[], cmdBuf[];
   //  ArrayBuild(cmdBuf, addr, reg);
   //  if (I2CBytes(port, cmdBuf, count, outBuf)) {
   //    if (count == 2)
   //      result = outBuf[1]*256 + outBuf[0];
   //    else
   //      result = outBuf[0];
   //  }
   //  return result;
   //}


   public PressureSensor(I2CPort port) {
      super(port);
      // TODO Auto-generated constructor stub
   }
   
   public int GetPressure()
   {
      //Method Header: PPS_ReadValue(byte port, byte reg,          byte count, byte addr)
      //Method Call:   PPS_ReadValue(S1,        PPS_REG_PRESS_ABS, 2,     PPS_ADDR)
      //Constants:              0x43             0x18
      
      byte[] outBuf = new byte[2];
      byte[] cmdBuf = new byte[2];

      cmdBuff[0] = 0x18;
      cmdBuff[1] = 0x43;

      //getData has no overload to input cmdBuff Array :/
      this.getData(0x43, outBuf, 2);

      int result = outBuf[1]*256 + outBuf[0];
      return result;
   }
   

}

[skoehler]

So in the constructor, you don't initialize the I2C address of the sensor. It is 0x18. You can use a call to the super constructor to initialize the I2C address.

Secondly, use this.getData(0x53, outBuf, 4); According to the userguide at mindsensors.com, that will give you the 4 bytes of the RAW reading (pressue in pascal).
Use the class EndianTools to convert the 4 byte array into an 32bit integer. According to the NXC examples, the 4 bytes will be little endian.

You don't need a cmdBuff array. In NXC, the first byte of the cmdBuff is the address of the sensor (0x18), and the second byte is the register (0x53). Using getData(0x53, ...) does the same thing, as long as the address of the sensor has been configured properly.

The mind sensors userguide recommends, that using the raw value at 0x53 instead of the converted value at 0x43 provides the best resolution. Hence, I would use 0x53 and convert pascal to PSI, bar, or whatever as needed in Java.

[fussel_dlx]

I've changed the code as you described:

Code: Select all

import lejos.nxt.I2CPort;
import lejos.nxt.I2CSensor;
import lejos.util.EndianTools;

public class PressureSensor extends I2CSensor {

   public PressureSensor(I2CPort port) {
      super(port,0x18, MODE_RAW, TYPE_CUSTOM);
      // TODO Auto-generated constructor stub
   }
   
   public int GetPressure()
   {
      byte[] outBuf = new byte[4];
      this.getData(0x53, outBuf, 4);
      
      return EndianTools.decodeIntLE(outBuf, 0);
   }
   
}

But it always returns 0, could you tell me what I have to type as "int off" in decodeIntLE?

[skoehler]

Please try
super(port, 0x18, I2CPort.LEGO_MODE, TYPE_LOWSPEED);

MODE_RAW and TYPE_CUSTOM won't work.

The off (which is short for offset) is the index of the first byte within the array. You use 0, which is correct.
Also, make sure to check the return value of getData() for errors.

[fussel_dlx]

Please try
super(port, 0x18, I2CPort.LEGO_MODE, TYPE_LOWSPEED);

MODE_RAW and TYPE_CUSTOM won't work.

The off (which is short for offset) is the index of the first byte within the array. You use 0, which is correct.
Also, make sure to check the return value of getData() for errors.

thank you very much its working now

Here's my final code for RAW output:

Code: Select all

import lejos.nxt.I2CPort;
import lejos.nxt.I2CSensor;
import lejos.util.EndianTools;

public class PressureSensor extends I2CSensor {

   public PressureSensor(I2CPort port) {
      super(port, 0x18, I2CPort.LEGO_MODE, TYPE_LOWSPEED);
      // TODO Auto-generated constructor stub
   }
   
   
   public int GetPressureInPascal()
   {
      byte[] outBuf = new byte[4];
      this.getData(0x53, outBuf, 4);
      
      return EndianTools.decodeIntLE(outBuf, 0);
   }
   
}

[skoehler]

Well, congratulations! Thanks for posting the code.
Do you object, if we include the driver with leJOS?
Could you try, whether you can use I2CPort.HIGH_SPEED instead of I2CPort.LEGO_MODE and it still works?

[fussel_dlx]

That would be very nice, feel free to use it.

I've tried your change and it's still working, I couldn't see any changes.

I hope this will help other noobs like me

[skoehler]

This class will be part of the next leJOS release:
https://sourceforge.net/p/lejos/code/69 ... ensor.java