Difference between revisions of "Week 4 Lab"

Revision as of 20:37, 20 April 2009

Interfacing

• Download and install processing http://processing.org/download

Serial Interface, for debugging

Sketchbook->Examples->Communication->ASCIITable

Basic text output from the microcontroller,

Serial.print()

and

Serial.println()

Use this to verify values and behavior inside of a program, for debugging. Examples:

• Displaying values of sensors Serial.print(val)
• Checking program flow.

Dimmer

Controlling a physical LED with the computer.

• Compile the Examples->Communication->Dimmer example, and upload it to your board. This example sets up communication on the serial port (in the void setup() function, and then reads values from the Serial input, and writes them to the ledPin output.
• Connect up the TIP120 driver circuit and motor from last week to the ledPin (pin 9). You should now be able to control the motor speed via the serial port on your computer... interesting...
• Click on the "Serial Monitor" button (to the right of the "Upload to Board" button) in the arduino software. Try sending different values to the board. Type in numbers and press Enter (or click on the "Send" button, either will work).
  • What behavior do you observe?
  • Can you get the motor to speed up or slow down?

modifying for rudimentary keyboard control

As-is, the Dimmer code is not very useful for controlling through the serial terminal like this. Now we are going to modify it to so that it works a little better. Our goal is to be able to set the speed of the motor typing the numbers 0-9 on the keyboard. 9 will go fastest (nearly full speed), and 0 will be a dead stop.

• Make a new copy of the Dimmer example, and replace the original loop() code with this new one:

void loop()
{
 char val;
 byte out_speed;
 // check if data has been sent from the computer
 if (Serial.available()) {
   // read the most recent byte (which will be from 0 to 255)
   val = Serial.read();
   
   if((val>='0')&&(val<='9')) {
     val=val-'0'; // set value between 0 and 9. 
     out_speed=val*28; // set out_speed between 0 and 252.
     analogWrite(ledPin, out_speed);
   } 
 }
}

• What I have done is change the Serial.read() and analogWrite() from before. Now we are reading a char rather than a byte from the Serial port, and we are checking whether this character it reads is one of the characters between '0' and '9': a letter on the keyboard was pressed, it is one of the numbers? If it is (if((val>='0')&&(val<='9'))) then we will set the speed of the motor proportionally.
• Compile and upload this sketch to the board, and try it out. Start the Serial Monitor again, and try sending the numbers 0-9 on the keyboard, the motor should speed up and slow down appropriately.
• EXPLANATION: What did we just do? The problem in our original Dimmer code was that the microcontroller was looking just at the binary value of the data it was receiving, but did not know what key was pressed. So, when we typed the number 0, which happens to have a binary value of ___ in the ASCII table, it will set the speed to that value, not to 0. We changed the program so the microcontroller is looking for the specific characters, '0' to '9', and then doing the appropriate math to set the output to the right speed.

controlling from a Processing app

Save your modified Dimmer example, and revert back to the original dimmer code. We are now going to learn how to control the processor from the processing App. See the commented Processing code hidden at the end of the Dimmer program.

• In Processing, open a new sketch, and copy this code into it. Save this sketch as "arduino_test" or something like that.
  • Try running this sketch. When you do, it may give you an error about "COM1" or something of that sort. You need to tell the program what serial port your arduino is connected to. On my computer, I see this output in the Processing window:

Available serial ports:

Stable Library
Native lib Version = RXTX-2.1-7
Java lib Version   = RXTX-2.1-7
[0] "/dev/tty.modem"
[1] "/dev/cu.modem"
[2] "/dev/tty.usbserial-A900acnt"
[3] "/dev/cu.usbserial-A900acnt"
[4] "/dev/tty.Bluetooth-PDA-Sync"
[5] "/dev/cu.Bluetooth-PDA-Sync"
[6] "/dev/tty.Bluetooth-Modem"
[7] "/dev/cu.Bluetooth-Modem"

• I know that my serial port is the "tty.usbserial-A900acnt", which is listed as device number 2 ([2]), so I go back into the processing code and change the line that says port = new Serial... to read port = new Serial(this, Serial.list()[2], 9600);
  • Now if I run the sketch again, I know that it will be properly communicating with the Arduino. You will need to modify that line to reflect whichever serial port your arduino is connected to.
• Upload the original (unmodified) Dimmer code to your arduino in the arduino software. Your processor should now be running that code... waiting for input!
• Run your newly created arduino_test sketch in processing. You will see a small graphic window, as you drag your mouse forwards and backwards across that window, your motor should speed up and slow down. Allright!! Now you have a simple graphical interface!

Pachube

http://www.pachube.com/ a service that enables you to connect, tag and share real time sensor data from objects, devices, buildings and environments around the world. The key aim is to facilitate interaction between remote environments, both physical and virtual."

Homework

With your sensor, build a simple computer/microprocessor project. Establish communication between the computer and processor, either controlling the device with commands from your computer program, or driving the computer program with information from the processor. You may use Processing, and adapt one of the simple examples we have seen in class, or you can use any other program you are comfortable with (Flash, MaxMSP, PD), so long as you can demonstrate it to us in class next week. We will take the first part of class to look at your ideas for these projects.

Extra

Connecting to various external devices and components: http://www.arduino.cc/playground/Main/ComponentLib