Asynchronous serial communication, which you’ll see demonstrated in this lab, is one of the most common means of communication between a microcontroller and another computer. You’ll use it in nearly every project, for debugging purposes if nothing else.<\/p>\n\n\n\n
The Processing sketch in this exercise graphs the incoming bytes. Graphing a sensor’s value like this is a useful way to get a sense of its behavior.<\/p>\n\n\n\n
These videos will help to understand this lab:<\/p>\n\n\n\n
- Video: Introduction to Serial Communication<\/a><\/li>
- Video: Serial Under the Hood: Interpreting Serial Data<\/a><\/li>
- Video: Reading Serial Input in Arduino<\/a><\/li>
- Video: Serial From Arduino to Processing<\/a><\/li><\/ul>\n\n\n\n
<\/span>What You\u2019ll Need to Know<\/span><\/h2>\n\n\n\n
To get the most out of this Lab, you should be familiar with the basics of programming an Arduino microcontroller. If you\u2019re not, review the Digital Input and Output Lab<\/a>, and perhaps the Getting Started with Arduino guide<\/a>.<\/p>\n\n\n\n
<\/span>Things You\u2019ll Need<\/span><\/h2>\n\n\n\n
Figure 1-3 are basically what you need for this lab.<\/p>\n\n\n\n
![\"Photo](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/pcomp-kit-f2019-arduino-nano-33-iot-150x150.jpg\")
Figure 1: Arduino Nano 33 IoT<\/figcaption><\/figure><\/div>\n\n\n\n ![\"Three](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/hookup_wire1-150x150.jpg\")
<\/a>Figure 2: 22AWG hookup wire<\/figcaption><\/figure><\/div>\n\n\n\n ![\"Potentiometer.](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/potentiometer3-150x150.jpg\")
<\/a>Figure 3: Potentiometer<\/figcaption><\/figure><\/div>\n\n\n\n <\/span>Connect the sensor<\/span><\/h2>\n\n\n\n
Connect your analog sensor to analog pin 0 like you did in the analog lab.<\/a> A potentiometer is shown here (Figure 4-6) because it’s easy, but you might want to pick a sensor that’s more interesting. IR distance rangers are fun for this exercise, for example. Force-sensing resistors are good as well.<\/p>\n\n\n\n
![\"Schematic](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/potentiometer_schem1-261x300.png\")
<\/a>Figure 4: Schematic view of a potentiometer connected to analog in 0 of the Arduino<\/figcaption><\/figure><\/div>\n\n\n\n ![\"Breadboard](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/potentiometer_bb-300x189.png\")
<\/a>Figure 5: Breadboard view of a potentiometer connected to analog in 0 of an Arduino<\/figcaption><\/figure><\/div>\n\n\n\n ![\"Breadboard](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/LabPotentiometerInNano_bb.png\")
Figure 6: Breadboard view of an Arduino Nano connected to analog in 0 of the nano (physical pin 4).<\/figcaption><\/figure><\/div>\n\n\n\n
\n\n\n\n<\/span>Read the Sensor Value and Send the Data Serially<\/span><\/h2>\n\n\n\n
Program the Arduino module to read the analog sensor and print the results to the Serial monitor. To do this, you’ll use the Arduino serial commands<\/a>. You’ve been using these in the digital and analog labs<\/a> to send data to the Serial Monitor. Instead of using the
Serial.println()<\/code> command as you did in those labs, however, useSerial.write()<\/code>. This will send the sensor value as a raw binary value rather than as a string:<\/p>\n\n\n\nvoid setup() {\n Serial.begin(9600);\n}\n\nvoid loop() {\n int analogValue = analogRead(A0)\/4; \/\/ read the sensor value\n Serial.write(analogValue); \/\/ send the value serially as a binary value\n}\n<\/pre><\/div>\n\n\n<\/span>Note: Why divide the sensor value by 4?<\/span><\/h3>\n\n\n\n
Dividing the sensor value by 4 reduces the range to 0 to 255, the range that can fit in a single byte.<\/p>\n\n\n\n
When you open the Serial Monitor, you will see garbage characters(Figure 7). What’s going on? The
Serial.write()<\/code> command doesn’t format the bytes as ASCII characters. It sends out the binary value of the sensor reading. Each sensor reading can range from 0 to 1023; in other words, it has a 10-bit range, since 210<\/sup> = 1024 possible values. Since that’s more than the eight bits that can fit in a byte, you’re dividing the value by 4 in the code above, to get a range from 0 to 255, or 28<\/sup> bits. For more background on this, see the notes on variables<\/a>.<\/p>\n\n\n\n![\"The](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/serial_monitor-300x215.png\")
<\/a>Figure 7: The Arduino IDE with the serial monitor open. The serial monitor screen is showing arbitrary characters. What is happening?<\/figcaption><\/figure><\/div>\n\n\n\n So, for example, if the sensor reading’s value is 234, then the
Serial.write()<\/code> command sends the binary value 11101010. If the reading is 255, thenSerial.write()<\/code> sends 11111111. If it’s 157, then the command sends 10011101. For more decimal-to-binary conversions, open your computer’s calculator and choose the Programmer view (press apple-3 on a mac, and Alt-3 on Windows).<\/p>\n\n\n\nWhen the Serial Monitor receives a byte, it and assumes it should show you the ASCII character<\/a> corresponding to that byte’s value. The garbage characters are characters corresponding to the ASCII values the Monitor is receiving. You’ll learn more about that in the two-way serial lab<\/a>.<\/p>\n\n\n\n
Sending data using
Serial.write()<\/code> is efficient for the computer, but it’s difficult to read. However, there are other ways to see the serial data. The serial terminal program CoolTerm<\/a> is available for Mac, Windows, and Linux. It gives you both an ASCII view of incoming bytes and a hexadecimal view (Figure 8). Download it and install it, and open the Options tab. From there, pick your serial port in the menu, then close the Options tab. Then click the Connect button to open the serial port. Related Video: Using CoolTerm<\/a><\/p>\n\n\n\n![\"The](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/CoolTerm-screenshot-1-300x251.png\")
<\/a>Figure 8: The CoolTerm serial terminal application showing the hexadecimal view.<\/figcaption><\/figure><\/div>\n\n\n\n NOTE: only one program can control a serial port at a time.<\/a> When you’re not using a given program, remember to close the serial port.<\/strong> You won’t be able to re-program the Arduino module if you don’t, because the serial terminal program will have control of the serial port.<\/p>\n\n\n\n
Once you have data coming into CoolTerm, click the Hex button. Instead of seeing the ASCII representation of the byte, you’ll see its hexadecimal value, with the ASCII characters down the side. As you change the sensor’s value, you’ll see the values change.<\/p>\n\n\n\n
Remember, the microcontroller is just sending a series of electrical pulses. How those pulses are interpreted is up to the program that reads them. In CoolTerm, you see two different interpretations, the hexadecimal value and the ASCII character corresponding to the value.<\/p>\n\n\n\n
For most projects, you\u2019ll set the port settings to 9600 bits per second, 8 data bits, no parity, one stop bit, and no hardware flow control. This will be set in the Preferences or Settings or Connection Options of whatever program you’re using. Once you\u2019ve applied those settings, open the serial port by clicking. Any bytes you type in the window will be sent out the serial port you opened. They won’t show up on the screen, however. Any bytes received in the serial port will be displayed in the window. Click the Disconnect button to close the serial port.<\/p>\n\n\n\n
<\/span>Read the Data in Processing<\/span><\/h3>\n\n\n\n
Related video: Basic Processing<\/a><\/p>\n\n\n\n
The serial monitor in Arduino and CoolTerm aren’t the only programs on your computer that can read data in from the microcontroller. Any program that can access the computer’s serial ports can do it. Processing<\/a> is an excellent tool for reading serial data because you can program it to interpret the data any way you want. Write a program to take in serial bytes and graph them.<\/p>\n\n\n\n
The first thing you need to do is to import the Processing Serial Library. This is a code library that adds functionality to Processing so it can read from and write to the computer’s serial ports. You can do this by choosing the Sketch menu, then
Import Library...-->serial<\/code>, or you can type:<\/p>\n\n\n\nProcessing code:<\/strong><\/p>\n\n\n
\nimport processing.serial.*;\n<\/div>\n\n\nTo use the serial library, create an instance of the library in a global variable as shown below:<\/p>\n\n\n\n
Processing code:<\/strong><\/p>\n\n\n
- Video: Serial Under the Hood: Interpreting Serial Data<\/a><\/li>
![\"Graphing](\"https:\/\/itp.nyu.edu\/physcomp\/wp-content\/uploads\/processing_graph_screenshot-300x242.png\")
<\/a>