You've already done this once. In Chapter 3, Providing Speech Input and Output, you edited the continuous.c code to allow it to call other programs to execute functionality. Here is the code that we used, found in the /home/ubuntu/pocketsphinx-0.8/programs/src/ directory.

The functionality that is important to us is the system("espeak "good bye""");"""); line of code. When you use the system function call, the program actually calls a different program, in this case the espeak program, and passes it to the good bye parameter so that the words good and bye come out of the speaker.

Here is another example, this time from Chapter 5, Making the Unit Mobile – Controlling Wheeled Movement, when we wanted to command our robot to move:

In this case, if you say forward to your robot, it will execute two programs. The first program you call is the espeak program with the parameter moving robot, and these words should then come out of the speaker on the robot. The second program is the dcmotor.py program, which should include the commands to move the robot forward.

I am now going to include an example in Python; it is my preferred language. I am going to use my wheeled robot:

It has a camera and is also able to communicate via a speaker. I control it via my wireless keyboard. I want to add the functionality to follow a colored ball, turn as the ball goes right or left, and tell me when it is turning.

You also need to make sure all of your devices are available to your programs. To do this, you'll need to make sure your USB camera as well as the two DC motor controllers are connected. To connect the camera, follow the steps given in Chapter 4, Allowing the BeagleBone Black to See, in the section Connecting the USB Camera to the BeagleBone Black and viewing the Images. It works best to connect the USB camera first before connecting any other USB devices.

After the camera is up and running, check that both motor controllers are available to the system. To do this, type cd /home/ubuntu/scm_linux and then type .SmcCmd –list. You should see something like this:

Both DC motor controllers are available. The numbers are the serial numbers of each individual motor; you can use them to send commands to just one motor controller. For example, you may need to send the resume command to the motors. To do this type as shown in the following screenshot:

I am going to involve three different programs. First, I am going to create a program that will find out if the ball is to the right or left. This is going to be my main control program. I am also going to create a program that moves my robot approximately 45 degrees to the right-hand side and another that moves my robot 45 degrees to the left-hand side. I am going to keep these very simple, and you might be tempted to just put them all in the same source file. But as the complexity of each of this program grows, it will make more sense for them to be separate, so this is a good starting point for your robotic code. Also, if you want to use the code in another project, or want to share the code, this sort of separation helps.

You are going to create three programs for this project. In order to keep this organized, I created a new directory in my home directory by typing mkdir robot in my home directory. I will now put all my files in this directory.

The next step is to create two files that can move your robot: one to the left-hand side, the other to the right-hand side. To do this, you will create two copies of the dcmotor.py code you created in Chapter 5, Making the Unit Mobile – Controlling Wheeled Movement, in your robot directory. If you have created that file in your home directory, type cp dcmotor.py ./robot/move_left.py cp dcmotor.py ./robot/move_right.py. Now you'll edit those, changing two numbers in the if __name__=="____=="__main__":__": command. Here is the edit to the move_left.py file:

I'm not going to explain the details of the code; it is already detailed in Chapter 5, Making the Unit Mobile – Controlling Wheeled Movement. The numbers that I changed were the motorx.setSpeed numbers; using 2000 for both motors turns my robot to the left-hand side. Additionally, I changed the time.sleep numbers to .1, so the robot will respond more quickly. The .1 will delay the execution of the program by one-tenth of a second. You will also need to edit moveright.py similarly:

This time the setSpeed numbers are both -2000, turning my robot to the right-hand side.

The final step is to create our main control program. Let's call it follow.py. Open this file with your editor; if using Emacs type emacs follow.py:

Let's look at this code:

Now you can run the program by typing sudo ./follow.py. The following window should be displayed:

The blue dot indicates that the program is following the green ball. As the green ball is moved towards the left edge, the robot should also rotate slightly left. As the green ball is moved toward the right edge, the robot should also rotate slightly right.

You can change the color that you are looking for by changing the line threshold = cv2.inRange(hsv,numpy.array((0, 155, 0)), numpy.array((255, 255,255))).

Two other color possibilities are:

With OpenCV it is also possible to do motion detection. There are a couple of good tutorials on how to do this with OpenCV. One simple example is at http://www.steinm.com/blog/motion-detection-webcam-python-opencv-differential-images/. Another example, a bit more complex but more elegant, is at http://stackoverflow.com/questions/3374828/how-do-i-track-motion-using-opencv-in-python.

When using motion detection, if you roll the ball across the screen, you should see the following output on the webcam (using the code from the second tutorial):

You can then use it to move the robot to follow the motion.