{"id":196,"date":"2014-09-29T21:09:10","date_gmt":"2014-09-29T21:09:10","guid":{"rendered":"http:\/\/itp.fromjia.com\/?p=196"},"modified":"2014-09-29T21:09:10","modified_gmt":"2014-09-29T21:09:10","slug":"lab-4-two-way-serial-communication","status":"publish","type":"post","link":"http:\/\/itp.fromjia.com\/?p=196","title":{"rendered":"Lab 4: Two-way serial communication"},"content":{"rendered":"

When reading multiple sensors a question that comes up is “which value corresponds with which sensor?” There are two ways to set sensor values in order: punctuation method<\/em>, which involves punctuating each set of data uniquely, and call-and-response (handshake) method<\/em>, which works very much like it sounds, sending one set of values at a time by setting the programs to call and respond to each other.<\/p>\n

We tried each method in this lab, neither worked very well for me. And I have a lot of questions regarding the additional code.<\/p>\n

This is what I’ve learned so far:<\/p>\n

Punctuation method<\/strong><\/p>\n

To send data from the Arduino, we use Serial.print()<\/strong> and Serial.println()<\/strong> to send\u00a0out each set of values, separated by commas Serial.print(“,”);<\/strong>.<\/p>\n

To receive the values in Processing, we add myPort.bufferUntil(‘\\n’);<\/strong>\u00a0in setup() so that the string of values would be saved to the buffer and read together. In the\u00a0serialEvent()<\/strong>\u00a0function, the string is read with myPort.readStringUntil(‘\\n’);<\/strong>.\u00a0Then\u00a0trim out any whitespace character (newline, carriage returns, spaces, tabs) with trim(stringx)<\/strong>, split the values at each comma with split(stringx, ‘,’);<\/strong>, convert the values into integers and store them in an array, for instance int<\/strong> sensor[] = int(split(stringx, ‘,’));<\/strong>.<\/p>\n

There are a few downsides to this method, namely the program may slow down if the buffer is full and that we can’t easily send binary values.<\/p>\n

Call-and-response\u00a0method<\/strong><\/p>\n

In the Arduino IDE, we setup a new function\u00a0establishContact()<\/strong>. This function sends out a message until receives data from Processing. We check for data by checking whether\u00a0Serial.available()<\/strong> is greater than 0 (true) or less then\/equal to 0 (false). We call for this new function in setup(). Then, with an if<\/strong>\u00a0statement, make sure that the strings of values in\u00a0loop() would only send when Serial.available() is greater than 0.<\/p>\n

In Processing, we check for contact with a new variable boolean firstContact = false;<\/strong>. In serialEvent() we let the program first check if the message from the Arduino is the right one with myString.equals()<\/strong>,\u00a0then send back a character with myPort.write()<\/strong> to start receiving actual data. If firstContact is true, the code from the rest of serialEvent() would run, trimming, splitting, converting, and storing the values.<\/p>\n

Issues:\u00a0<\/strong><\/p>\n