Sending Data from a computer to a microcontroller using a UART (Universal Asynchronous Receiver/Transmitter) Eric Bell 04/05/2013 Abstract: Serial communication is the main method used for communication between external microcontrollers and computers, and can be a challenge to set up correctly. This application note will provide a walk-through example on how to set up a simple UART communication link using Microsoft Visual Studio and the Arduino Leonardo microcontroller. Keywords: Arduino, Leonardo, Visual Studio, Microcontroller, UART Page 1
Table of Contents Introduction...3 Arduino Software Installation...4 Hardware Setup...4 Setting up the Receiver.5 Setting up the Sender.6 Recommendations.9 References..9 Page 2
Introduction: This application note will provide instructions on how to obtain simple communications between a computer and a microcontroller using UART (Universal Asynchronous Receiver/Transmitter). UART is a commonly used piece of hardware which translates data between parallel and serial communication mediums (See reference [6]). In this tutorial, you will be taught how to set up a simple interface between a computer and a microcontroller by utilizing Microsoft Visual Studio, and the Arduino Leonardo microcontroller. The implementation described in this application note will provide a walk-through to set up the Arduino Leonardo to receive communication from the computer and then respond appropriately. In this case, the microcontroller will receive characters from the computer consisting of either + or -. These characters will activate an LED by turning it on or off, by interpreting a + as an on signal, and a - as an off signal. Implementation: Hardware: Software: - Personal Computer running Microsoft Windows - Arduino Leonardo Microcontroller - Micro-USB Interconnect Cable - 1 LED (any color) - 1 220-Ohm resistor - Microsoft Visual Studio - Arduino IDE Software - Arduino Leonardo Drivers Page 3
Arduino Software Installation Download and install the Arduino IDE Software and Arduino Leonardo Drivers by following the set-up instructions provided with the software. Arduino IDE Software and Leonardo Drivers can be obtained free of charge by download by visiting http://arduino.cc/en/main/software. Hardware Setup For this communications set-up, we will be physically connecting the Arduino Leonardo microcontroller to the computer using a micro-usb interconnect cable, and setting up the microcontroller to provide feedback through the lighting of an LED. The microcontroller can be obtained by ordering, and is available at many different web sites on the internet. One major distributor of Arduino products is Mouser, and this microcontroller can be ordered from them by visiting www.mouser.com/arduino-leonardo. Follow the steps outlined below for proper set-up: 1) Connect the 220-ohm resistor and LED to the Arduino Leonardo microcontroller by following the diagram below. (See Reference [1]) 2) Plug the Micro-USB cable in to the Arduino Leonardo in to the attached port, and in to any available USB port on the computer. Page 4
Setting up the Receiver The Arduino Leonardo microcontroller needs to be set up to receive a character from the USB port, and also needs to be programmed to respond appropriately based upon the received character. This will be accomplished by using the Arduino IDE Software and the following code (See reference [1]): int led = 13; char c; void setup() pinmode(led, OUTPUT); // specify led port as output Serial.begin(9600); // Specify serial communications speed void loop() if(serial.available() > 0) c = Serial.read(); // reads a character from serial interface Serial.print(c); if(c == '+') digitalwrite(led, HIGH); // turn on LED else if(c == '-') digitalwrite(led, LOW); // turn off LED The code above is written in C#, and will specify port 13 as the port for our LED, and will determine whether the Arduino Leonardo will turn on or turn off the LED. Once this code has been typed in to the Arduino IDE software, it can be uploaded by clicking on File-> Save, and then clicking on the Upload button. The button is depicted as a small arrow in the upper left corner of the program screen. Page 5
Setting up the Sender For this portion of the set-up, we will be using Microsoft Visual Studio to create a program which will send the + or - character to the Arduino Leonardo microcontroller through the USB cable. This portion of the application note will provide a demonstration on how to write code that will: 1) Determine if there is a serial port currently available for communication 2) Open the serial port for communications 3) Send data through the serial port 4) Close the serial port Microsoft Visual Studio should be used to create a new project, in which you should create one combo-box, and four buttons. This can be accomplished within the program by clicking on The toolbox icon on the left side of the screen, and then double-clicking on the Button link. This will allow you to place the button on your blank form. Once all buttons have been placed, doubleclick on the ComboBox link in order to place the drop-down menu as shown in the figure. Complete instructions are included in the Microsoft documentation on their web site (Reference [4]). When complete, your program GUI (Graphics User Interface) should look similar to this: The code on the following pages will then be used to control the functions of the combo-box and buttons. Page 6
Example code to determine if there is a serial port currently available (See reference [2]): private void Form1_Load(object sender, EventArgs e) foreach (string port in SerialPort.GetPortNames()) // Adds all port names to ports list cbports.items.add(port); // adds ports to Ports combo-box if (cbports.items.count > 0) // if there is at least one port available, select the first one as default cbports.selectedindex = 0; else // no ports available cbports.enabled = false; MessageBox.Show("Could not locate any available serial ports.", "No serial ports", MessageBoxButtons btnsenda.enabled = false; btnsendb.enabled = false; btnclose.enabled = false; Page 7
Example code to open the serial port for communication (See reference [3]): private void btnopen_click(object sender, EventArgs e) _serialport = new SerialPort(cbPorts.Text); // Store serial ports in combo-box _serialport.baudrate = 9600; // Set Port speed _serialport.databits = 8; // Use 8 bits for data _serialport.parity = Parity.None; // No Parity _serialport.stopbits = StopBits.One; _serialport.open(); // Open the port _serialport.writetimeout = 5000; // set time-out time for write // Change the Enabled flag for the buttons to prevent user error cbports.enabled = false; btnopen.enabled = false; btnsendplus.enabled = true; btnsendminus.enabled = true; btnclose.enabled = true; Example code to write a + to the open serial port (See reference [3]): private void button1_click(object sender, EventArgs e) _serialport.writeline("+"); // Writes a '+' to the open Serial Port Example code to close the serial port (See reference [3]): private void btnclose_click(object sender, EventArgs e) _serialport.close(); // Change the Enabled flag for the buttons to prevent user error cbports.enabled = true; btnopen.enabled = true; btnsendplus.enabled = false; btnsendminus.enabled = false; btnclose.enabled = false; Page 8
In this application note, we have covered the set up of the hardware, the design and programming of the user interface, as well as the programming of the Arduino Leonardo firmware. By following these instructions, it should be a very straight-forward task to develop communication between the computer and the Arduino Leonardo microcontroller. Once these techniques have been practiced, they can be applied to more complex situations, as well as to other microcontrollers. Recommendations - The Arduino Leonardo can also be used to send date to the computer using the serial interface. There are many examples and tutorials available for free by utilizing the Arduino web site. (See reference [1]) - The serial ports on the Arduino Leonardo can be used to communicate to more complex devices, such as other microcontrollers - More complex Arduino Microcontrollers are capable of communication through a much wider array of communication mediums, such as WiFi, rather than just serial communication References [1] http://arduino.cc/en/tutorial/homepage [2] http://msdn.microsoft.com/en-us/library/tf8zk72w.aspx [3] http://msdn.microsoft.com/en-us/library/y2sxhat8.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-2 [4] http://msdn.microsoft.com/en-us/vstudio/aa718325.aspx [5] http://en.wikipedia.org/wiki/universal_asynchronous_receiver/transmitter Page 9