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How to send message from NXT to an external device

Question


I am using the NXT to control an Arduino based robot.
I am able to receive commands on the Arduino computer from NXT via bluetooth.
I am trying to understand the commands sent from the NXT

I have been reading the “Programming LEGO NXT” section of RobotAppStore’s knowledge base and have learned a lot – it was great.

Do you know if there is a source to un...
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LEGO NXT Cannot Play a Sound File

Question


I cannot play a sound file.

The PlaySoundFile command (0x02) returns a success 0x00 as a command status but the sound file is not played.

What could be the reason for that?

Answer


There are several possible reasons for the NXT to ignore the PlaySoundFile command:
  • Wrong loop argument- loop argument can only be 0x00 for playing once or 0x01 for loop;
  • The volume on the NXT’s brick is...
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LEGO NXT Cannot Play a Tone

Question


I am trying to play a tone using the PlayTone command (0x03).
I’ve checked the syntax of the command, and it seems correct.
What am I missing?

Answer


There are several possible reasons that the PlayTone commands are being ignored:
  • Wrong command arguments- The frequency and duration are constructed from 2 bytes each. Low byte should come first.
  • The volume on the NXT’s brick is set to 0;

In order ...
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LEGO NXT Cannot Synchronize All the Motors

Question


I am trying to synchronize all the three motors of my LEGO NXT 2.0 using the SetOutputState command.

I’ve sent the following command:
0x0C 0x00 0x00 0x04 0x0FF 0x32 0x05 0x02 0x00 0x20 0x00 0x00 0x00 0x00

All the motors are running, but it seems that they are not synchronized.

Answer


Only two motors can be synchronized.

In case you’ve set all the three motors to be synchronized, the synchronizati...
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LEGO NXT Create file command is ignored

Question


I am trying to programmatically download a sound file to the NXT’s brick.

According to the tutorial, the way to download a sound file programmatically to the brick is:
  • Create an empty file on the brick using the FileOpenWriteCreate command;
  • Use the FileWrite command to fill the empty file with the sound file bytes;
  • Call to FileClose command to save changes and close;

I can’t make the FileOpenWriteCreate to work. It seems th...
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LEGO NXT FileWrite returns 0x84 error

Question


I keep getting the 0x84 error- End of file expected, from the FileWrite command (0x83).

The amount of bytes that are sent using the FileWrite command are the same as I’ve used when creating the file.
The file is opened for writing;

What am I missing here?

Answer


There are several possible reasons for the 0x84 error when using the FileWrite after creating a file:
  • Small file size- the actual size of the file that ...
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LEGO NXT ignores the file size when it is created

Question


I am using the TextFileOpenWriteCreate command (0x8B).
The file that is actually created is smaller than the size that I send to the command.

Is that a bug in the communication protocol?

Answer


There are two possible reasons for the reduced file size:
  • Wrong command arguments- The size argument contains 4 bytes LSB first. If the bytes are mixed (MSB first), the file that is created will be different;
  • Automatica...
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LEGO NXT Issues with Motors Ramp Up Command

Question


I am working on a project that is a game using two Lego NXT 2.0.

I came across a strange behavior, whenever I send the ramp-up command:
1. Motor are not reacting;
2. There is a strange high pitch noise;

The command that I send to Lego NXT brick is:
0x0C 0x00 0x00 0x04 0x0FF 0x64 0x04 0x02 0x00 0x10 0x01 0x00 0x00 0x00

Answer


It sounds like an interesting project. We are looking forward to publishin...
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LEGO NXT Motors Are Not Running

Question


I can’t make the LEGO NXT 2.0 motors running.
Neither of the following commands, has worked:

Regulated motor mode, synchronized motors
0x0C 0x00 0x00 0x04 0x0FF 0x64 0x04 0x02 0x00 0x20 0x00 0x00 0x00 0x00

Regulated motor mode, speed regulation
0x0C 0x00 0x00 0x04 0x0FF 0x64 0x04 0x01 0x00 0x20 0x00 0x00 0x00 0x00

Break motor mode
0x0C 0x00 0x00 0x04 0x0FF 0x64 0x02 0x00 0x00 0x20 0x00 0x00 0x00 0x00
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LEGO NXT PlaySoundFile Returns 0xC0 error

Question


PlaySoundFile command (0x02) is not working, and I keep getting the 0xC0 error as a command status in the reply message.

How to make LEGO NXT to play a sound file?

Answer


There are several possible reasons for the Out of Range 0xC0 error message when playing a sound file:
  • Wrong loop argument- loop argument can only be 0x00 for playing once or 0x01 for loop;
  • Wrong file name argument- m...
    Read More ->

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