Sariel.pl

A method and a program for controlling up to 7 NXT units simultaneously using Bluetooth and a standard control pad.  

I was convinced that there can be only one connection between PC and a NXT unit at a time, until Kirby00216 prompted me to run several instances of ROBOTC at the same time, each connected to a different unit. Using this method, I have created a simple control program that can be run on a number of NXT units, allowing to control all of them with a single controller – in this case, a standard USB control pad. I have used a method of reading NXT unit’s unique ID developed by Xander to allow unit-specific commands in the program. In other words, even though the same program is running on all units simultaneously, it’s possible to specify which unit is supposed to respond to which commands.

In case of my sample program provided below, there are two NXT units which I call NXT1 and NXT2, and their unique IDs are 1313750 and 911538 respectively. When you run this program on any unit, it shows the unit’s unique ID, so you can add it to the program and specify commands for that particular unit.

I only own 2 NXT units, but according to the Bluetooth specification, it’s possible to connect up to 7 units at a time to the PC this way. You can notice on the video that there are slight delays in units’ reaction when commands are being sent to two different units at the same time – this is probably caused by the PC’s outgoing Bluetooth queue. Still, this solution has a large potential, as a typical control pad with 2 joysticks and 12 buttons can be used to control 10 motors at the same time.

Control program:

#include "JoystickDriver.c"

task main () {
  long uniqueID = 0;
  TBTAddress btAddr;
  getBTAddress(btAddr);
  uniqueID = (long)btAddr[5] + ((long)btAddr[4] << 8) + ((long)btAddr[3] << 16);

  while(true)
  {
    getJoystickSettings(joystick);

    if(uniqueID == 1313750){ // NXT1 unit
      if(joy1Btn(1) == 1)
        motor[motorA] = 100;
      else
        motor[motorA] = 0;

      if(joy1Btn(2) == 1)
        motor[motorB] = 100;
      else
        motor[motorB] = 0;

      if(joy1Btn(3) == 1)
        motor[motorC] = 100;
      else
        motor[motorC] = 0;
    }

    else if(uniqueID == 911538){ // NXT2 unit
      if(joy1Btn(5) == 1)
        motor[motorA] = 100;
      else
        motor[motorA] = 0;

      if(joy1Btn(6) == 1)
        motor[motorB] = 100;
      else
        motor[motorB] = 0;

      if(joy1Btn(7) == 1)
        motor[motorC] = 100;
      else
        motor[motorC] = 0;
    }

    nxtDisplayCenteredTextLine(0, "BATTERY: %3.1fV", nImmediateBatteryLevel / (float) 1000);
    nxtDisplayCenteredTextLine(1, "UNIT: %d", uniqueID);
  }

}
									

Video: