The timing diagram of waveform on each pin is shown in the following diagram. We need to apply a short 10 µs pulse to the trigger input to start the ranging and then the module will send out an eight cycle burst of ultrasound at 40 KHz and raise its echo. The echo is a distance object that is pulse width and the range in proportion. You can calculate the range through the time interval between sending trigger signals and receiving echo signals using the following formula:

Range = high level time of echo pin output * velocity (340 M/S) / 2.

It will be better to use a delay of 60 ms before each trigger, to avoid overlapping between the trigger and echo:

The following Energia code for Launchpad reads values from the ultrasound sensor and monitors the values through a serial port.

The following code defines the pins in Launchpad to handle ultrasonic echo and trigger pins and also defines variables for the duration of the pulse and the distance in centimeters:

const int echo = 9, Trig = 10;
long duration, cm;

The following code snippet is the setup() function. The setup() function is called when a sketch/code starts. Use this to initialize variables, pin modes, start using libraries, and so on. The setup function will only run once, after each power up or reset of the Launchpad board. Inside setup(), we initialize serial communication with a baud rate of 115200 and setup the mode of ultrasonic handling pins by calling a function SetupUltrasonic();

void setup()
{
  
  //Init Serial port with 115200 buad rate
  Serial.begin(115200);  
  SetupUltrasonic();  
}

The following is the setup function for the ultrasonic sensor; it will configure the Trigger pin as OUTPUT and the Echo pin as INPUT. The pinMode() function is used to set the pin as INPUT or OUTPUT.

void SetupUltrasonic()
{
 pinMode(Trig, OUTPUT);
 pinMode(echo, INPUT); 
  
}

After creating a setup() function, which initializes and sets the initial values, the loop() function does precisely what its name suggests, and loops consecutively, allowing your program to change and respond. Use it to actively control the Launchpad board.

The main loop of this is in the following code. This function is an infinite loop and calls the Update_Ultra_Sonic() function to update and print the ultrasonic readings through a serial port:

void loop()
{
    Update_Ultra_Sonic();
    delay(200);
}

The following code is the definition of the Update_Ultra_Sonic() function. This function will do the following operations. First, it will take the trigger pin to the LOW state for 2 microseconds and HIGH for 10 microseconds. After 10 microseconds, it will again return the pin to the LOW state. This is according to the timing diagram. We already saw that 10 µs is the trigger pulse width.

After triggering with 10 µs, we have to read the time duration from the Echo pin. The time duration is the time taken for the sound to travel from the sensor to the object and from the object to the sensor receiver. We can read the pulse duration by using the pulseIn() function. After getting the time duration, we can convert the time into centimeters by using the microsecondsToCentimeters() function, as shown in the following code:

void Update_Ultra_Sonic()
{
  digitalWrite(Trig, LOW);
  delayMicroseconds(2);
  digitalWrite(Trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(Trig, LOW);

  duration = pulseIn(echo, HIGH);
  // convert the time into a distance
  cm = microsecondsToCentimeters(duration);
  
  //Sending through serial port
  Serial.print("distance=");
  Serial.print("	");
  Serial.print(cm);
  Serial.print("
");
  
}

The following code is the conversion function from microseconds to distance in centimeters. The speed of sound is 340 m/s, that is, 29 microseconds per centimeter. So we get the total distance by dividing the total microseconds by 29/2:

long microsecondsToCentimeters(long microseconds)
{
return microseconds / 29 / 2;
}

After uploading the code, open the serial monitor from the Energia menu under Tools | Serial Monitor and change the baud rate into 115200. You can see the values from the ultrasonic sensor, like this:

Output of the energia serial monitor

In this section, we can see how to connect Tiva C LaunchPad with Python to receive data from Launchpad.

The PySerial module can be used for interfacing Launchpad to Python. The detailed documentation of PySerial and its installation procedure for Window, Linux, and OS X is on the following link:

http://pyserial.sourceforge.net/pyserial.html

PySerial is available in the Ubuntu package manager and it can be easily installed in Ubuntu using the following command in terminal:

$ sudo apt-get install python-serial

After installing the python-serial package, we can write a python code to interface Launchpad. The interfacing code is given in following section.

The following code imports the python serial module and the sys module. The serial module handles the serial ports of Launchpad and performs operations such as reading, writing, and so on. The sys module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter. It is always available:

#!/usr/bin/env python
import serial
import sys

When we plug Launchpad to the computer, the device registers on the OS as a virtual serial port. In Ubuntu, the device name looks like /dev/ttyACMx. Where x can be a number, if there is only one device, it will probably be 0. To interact with the Launchpad, we need to handle this device file only.

The following code will try to open the serial port /dev/ttyACM0 of Launchpad with a baud rate of 115200. If it fails, it will print Unable to open serial port.

try:
    ser = serial.Serial('/dev/ttyACM0',115200)
except:
    print "Unable to open serial port"

The following code will read the serial data until the serial character becomes a new line (' ') and prints it on the terminal. If we press Ctrl + C on the keyboard, to quit the program, it will exit by calling sys.exit(0).

while True:
    try:
        line = ser.readline()
        print line
    except:
        print "Unable to read from device"
        sys.exit(0)

After saving the file, change the permission of the file to executable using the following command:

$ sudo chmod +X script_name
$ ./script_name

The output of the script will look like this: