US sensors in single shot mode (ping mode)

[HaWe]

from a former nxtasy thread:
reading US sensors in single shot mode (ping mode; original code modified):

Code: Select all

//multi US single shot

// 1 US sensor at port 0=S1
// 1 US sensor at port 1=S2

#define printf2( _x, _y, _format1, _format2, _value1, _value2) { \
  string sval1 = FormatNum(_format1, _value1); \
  string sval2 = FormatNum(_format2, _value2); \
  string s =sval1+sval2; \
  TextOut(_x, _y, s); \
}



void USSingleShot(byte port, int &echo)
{
   byte ping_cmnd[] = {0x2, 0x41, 0x1};  // sensor one-shot-mode command
   byte register_select[] = {0x2, 0x42}; // sensor data register

   byte data_size=4;
   byte data[4];                 // =data_size, up to 4 echoes

   I2CWrite(port, 0, ping_cmnd);
   Wait(40);                     // waiting time shortened!
   if (I2CBytes(port, register_select, data_size, data)) {
      echo=data[0]; }            // 1st echo

}

task main()
{
   int
   e_left,   // US-Echodaten von US Sensor an port 0 (S1)
   e_right;  // US-Echodaten von US Sensor an port 1 (S2)

   SetSensorLowspeed(0);
   SetSensorLowspeed(1);

   while(true)
   {
      USSingleShot(0, e_left);
      Wait(40);
      USSingleShot(1, e_right);

      printf2( 0, 0, "%4d", "       %4d",  e_left, e_right);

      Wait(40);
   }
}

[muntoo]

Alternatively, you can use:

Code: Select all

void USSingleShot(byte port, int &e1)
{
	WriteI2CRegister(port, I2C_ADDR_DEFAULT, I2C_REG_CMD, US_CMD_SINGLESHOT);
	e1 = SensorUS(port);
	//byte values[];
	//ReadSensorUSEx(port, values);
	//e1 = values[0];
}

OR

Code: Select all

byte USSingleShot(byte port)
{
	WriteI2CRegister(port, I2C_ADDR_DEFAULT, I2C_REG_CMD, US_CMD_SINGLESHOT);
	//byte values[];
	//ReadSensorUSEx(port, values);
	//return(values[0]);
	return(SensorUS(port));
}

[HaWe]

is that newly added to the API recently?

US_CMD_SINGLESHOT
surely is predefined in the internal Nxtdefs.h,

but what are the values of
I2C_ADDR_DEFAULT,
I2C_REG_CMD
?

[mightor]

The default I2C address for an NXT sensor is 0x02 and the default command register is 0x41. This can be found in the official Lego specification documents.

Regards,
Xander

[mattallen37]

Just to clarify, those are the LEGO defaults. Most of the HT sensors also conform the the defaults, but some of the mindsensors products do not.

[HaWe]

thx, so the code is always equal to this ( just to clarify):

Code: Select all

byte USSingleShot(byte port)
{
   WriteI2CRegister(port, 0x02, 0x41, US_CMD_SINGLESHOT);
   //byte values[];
   //ReadSensorUSEx(port, values);
   //return(values[0]);
   return(SensorUS(port));
}

[mattallen37]

That looks right.

Since the macros are constants, you can easily find the value yourself, like this (note, this displays in decimal format).

Code: Select all

task main()
{
  NumOut(0,LCD_LINE1,I2C_ADDR_DEFAULT); //display the value of the macro
  NumOut(0,LCD_LINE2,I2C_REG_CMD);      //display the value of the macro
  NumOut(0,LCD_LINE3,US_CMD_SINGLESHOT);//display the value of the macro
  while(true);  //Wait forever
}

[HaWe]

thx, but I never heard of those parameters before, and I assumed they might be variables, not universal / general constants.

I couldn't imagine that e.g. I2C_ADDR_DEFAULT always is 0x02 because I assumed each single sensor could have it's specific default address.
The same it's with I2C_REG_CMD.

But:
I2C_US_ADDR_DEFAULT (0x02)
and
I2C_US_REG_CMD (0x41)
instead would have been unambiguously (unequivocally?).

But now I see, thx again!

ps
And so I guess that
US_CMD_SINGLESHOT
is 0x42...(?)

Code: Select all

byte USSingleShot(byte port)
{
   WriteI2CRegister(port, 0x02, 0x41, 0x42);
   //byte values[];
   //ReadSensorUSEx(port, values);
   //return(values[0]);
   return(SensorUS(port));
}

[mightor]

Doc,

Almost all of Lego's sensors use 0x02, with the exception of the temp sensor (that uses 0x98 and is -nothing- like the normal Lego sensors). There is a default memory (register) layout, which usually looks like this:
0x00 : Version
0x08 : Product ID
0x10 : Sensor Type
0x41 : command register
0x42 : start of data registers

There are exceptions, but this tends to be the layout most sensor use. Mindsensors does deviate from this a lot more than HiTechnic does but both companies play by different rules.

The reason the Lego temp sensor is different is because it doesn't use a custom chip in it made by Lego itself, rather an off-the-shelf Texas Instruments temp sensor. So Lego had no say in how it should function.

Edit: added PDF with I2C commands for Sonar Sensor.

- Xander

[HaWe]

Xander,
thx, very interesting indeed.
Comparing matt's code with the one I posted I found that in "mine" one had to declare the lenght of the data registers (count of bytes).
That's not in matt's code.
Why does it work though?

edit:
thx for your appendix, but to be honest: I don't understand a single line ;)