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Use the program Voice Bot for the Voice Controlled Car.  The program uses a couple of tricks to distinguish between the four voice commands that the robot can understand.  Actually, real computer voice recognition programs use tricks too (just better and much more complicated), because no computer really understands what you are saying.

It takes a little practice to learn how to say the words in the right way for it to work (see the instructions below), so the program also draws a graph of the sound that it hears on the NXT's display to help you practice saying the sounds right.

The NXT's sound sensor is very simple and is only capable of measuring the loudness of sound that it hears, so the Voice Bot program uses a few simple tricks based on the loudness and timing of your voice to determine what command you are saying.  It will take a little practice to learn to say the commands properly, so the program helps out by drawing a graph of the "shape" and timing of your voice that it hears. 

Here is a description of how each command should sound, along with a picture of what the graph might look like for that sound on the NXT's display:
 

The "Go" command must be a short sound with no noise afterwards.  The tick mark that shows the position of the loudest part of the sound on the graph must be in the left part of the graph.	The only command that the robot understands when it is going forward is "Stop".  So, you must be stopped before doing any turns.  Also, the "Stop" command must be pretty loud, to get through the noise of the motors when the robot is moving.
The "Turn Right" command must be said with "Right" louder than "Turn", and at a fairly normal speaking speed.  The tick mark that shows the position of the loudest part of the sound on the graph must be in the middle part of the graph.	The "Turn Left" command must be said with "Left" louder than "Turn", and a brief pause between the two words (otherwise it will sound just like "Turn Right" to the program).  The tick mark that shows the position of the loudest part of the sound on the graph must be in the right part of the graph.

So, the four voice commands must be said something like this:

• "Go"

• "STOP!!"

• "Turn RIGHT!"

• "Turn ... LEFT!"

And remember that when the robot is moving forward you can only give the "Stop" command, and when the robot is stopped you can only give the "Go", "Turn Right", or "Turn Left" commands.

Finally, you must pause for about a second between voice commands, to allow there to be some quiet between commands, so you can't yell "Turn Right" immediately after saying "Stop", for example.

The key to getting the "Go", "Turn Right", and "Turn Left" commands right is the timing of the loudest part of the command.  Note that the graph is divided into three parts by the two vertical lines, and the program will draw a tick mark along the horizontal line at the top of graph where the loudest part of the command was heard:

• If the tick mark ends up in the left part of the graph, it will be "Go".

• If the tick mark ends up in the middle part of the graph, it will be "Turn Right". 

• If the tick mark ends up in the right part of the graph, it will be "Turn Left".

You can practice the timing of your commands with the robot held in your hands and speaking at a normal talking volume.  Note that when you do this, the clattering of the wheels spinning in the air when the robot is "going" may cause a "Stop" command to be heard when you didn't say one.  You can take the wheels off for practice if this is a problem.  Then when the robot is on the floor and you are standing over it talking to it, you will need to talk louder for it to hear you well enough.

Adjusting the Sound Levels

If you are having trouble with the car stopping by itself before you say "Stop", or going or turning before you say anything, you may need to adjust some of the numbers used in the program, because currently the program does not have any "calibration" for the sound levels, and some sound sensors are more sensitive than others (and some rooms are more noisy than others).  The first three blocks in the Voice Bot program set three variables to numbers that are the sound levels required for the various commands to work:

You can change one of these sound levels by selecting the block and changing the "Value" for the variable.  If the robot stops before you say "Stop", try increasing the value for the Stop variable.  If the robot goes or turns before you say anything, try increasing the value for the Go variable.   If your room is very noisy and the robot doesn't seem to listen to anything after hearing one command, you could try increasing the Quiet variable.

• Practice saying the four commands so that the robot can understand them, then see if you can control the robot using only your voice to drive around your house.  Make sure you understand all the rules explained above.

• The Voice Bot program is complex, but if you know something about NXT programming, open it and take a look at parts of it and see if you can understand how any part of it works.  Try looking at just small parts of it at time and read the comments that describe those parts.  If you can find the parts that control the motors, you could modify the program to make a new program to control something else that did different things in response to similar-sounding voice commands.  Actually, the voice commands you use don't even need to sound similar, they just need to follow the same rules of the tricks that this program uses.

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