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Published December 4, 2018

Texas Instruments RSLK with Ultrasonic Distance Sensors

Ultrasonic distance sensors are affordable, accurate, and easy to use. So I integrated these sensors onto the basic RSLK by TI.

IntermediateFull instructions provided11,385

Texas Instruments RSLK with Ultrasonic Distance Sensors

Things used in this project

Hardware components

Texas Instruments TI Robotics System Learning Kit TI-RSLK

Ultrasonic Sensor - HC-SR04 (Generic)

Mini Solderless Bread Boards

Software apps and online services

Texas Instruments Code Composer Studio

Texas Instruments tirslk_maze

Story

Ultrasonic distance sensors are affordable, accurate, and easy to use. So as part of my involvement in an independent undergraduate research class at UCI, my goal was to integrate these sensors onto the Texas Instruments (TI) Basic Robotic System Learning Kit (RSLK) in place of the infrared sensors that come with the Advanced kit. I was successfully able to augment the TI-RSLK with these sensors and will provide details on how I accomplished this.

I began to integrate the distance sensors with the robot after assembling the TI-RSLK, installing Code Composer Studio (CCS), importing the RSLK files, and programming the motors in Lab 12 or 13 of TI's free online curriculum, You can find more information about the TI-RSLK curriculum at https://training.ti.com/ti-robotics-system-learning-kit or sites.uci.edu/orange. I used some mini breadboards to connect the sensors to Launchpad of the RSLK. Each distance sensor has four pins: Vcc, Echo, Trigger, and Ground. I connected each Vcc to a separate 5V pin on the launchpad, and the grounds are connected to the same ground pin. The other connections made from the robot to launchpad are listed below.

Middle Distance Sensor:

TriggerPin: P6.4

EchoPin: P6.5

Left Distance Sensor:

TriggerPin: P6.0

EchoPin: P3.2

Right Distance Sensor:

TriggerPin: P4.1

EchoPin: P3.3

After making these connections, I began writing the code for the distance sensors. The source code for a single ultrasonic distance sensor, and three ultrasonic distance sensors are attached to this project. The source code includes many comments, so it should be easy to read and understand most of the code. However, I will discuss the main functions of the code here.

First, the void Distance_Init(void) function is used to set the launchpad pins to GPIO, echo pins to inputs, and trigger pins to outputs. This function must be called in the main function.

Next, the void SetDistance(int timeOut) functions are used to set the current distance fora sensor. There is a separate function for each distance sensor. The timeOut variable is used to limit the amount of time the distance sensors wait for the echo signal. Without the timeOut variable, this function could end up in an infinite loop.

The void CheckDistance(void) is a function that is periodically called using a timer interrupt. This function analyzes if the distance sensors have detected an object that is closer than a specific threshold value.

void AvoidObject(void) is a function that is called when an object is detected by the sensors. These functions currently contain code that simply tells the robot to turn in the opposite direction of the object detected.

In the int main(void), the robot is programmed to drive forward until an object is detected. It is important to initialize the motor, and launchpad, and enable interrupts in the main.

Additional information and resources about the RSLK can be found at sites.uci.edu/orange

Here are some videos of the RSLK with the ultrasonic distance sensors.

The Motor speed was actually set to 5000

In the video above, the robot experienced some difficulties due to the walls being too short so the distance sensors were not always able to detect them.

Code

#include <stdint.h>
#include "msp.h"
#include "../inc/Clock.h"
#include "../inc/CortexM.h"
#include "../inc/LaunchPad.h"
#include "../inc/Motor.h"
#include "../inc/TimerA1.h"



int distance;

//Trigger pin conected to P6.4
uint8_t trigBit = 0x10;

//Echo pin onnected to P6.5
uint8_t echoBit = 0x20;

void Distance_Init(void){
    //Trigger as GPIO, P6.4
    P6->SEL0 &= ~trigBit;
    P6->SEL1 &= ~trigBit;
    //Trigger as Output
    P6->DIR |= trigBit;

    //Echo as GPIO P6.5
    P6->SEL0 &= ~echoBit;
    P6->SEL1 &= ~echoBit;
    //Echo as input
    P6->DIR &= ~echoBit;
}


int GetDistance(int timeOut){
    //timeOut is a value in microseconds
    //it is used to exit the while loop if the signal is not found

    int time;
    //int distance;
    uint8_t echoValue;

    //Trigger off
    P6->OUT &= ~trigBit;
    Clock_Delay1us(2);

    //Trigger on
    P6->OUT |= trigBit;
    Clock_Delay1us(10);

    //Trigger off
    P6->OUT &= ~trigBit;

    time = 0;

    //Store the value of the echo sensor ANDing the pin vector with the bit that the eacho sensor is connected to
    echoValue = (P6->IN & echoBit);

    //wait for triggers signal to be received by the echo sensor
    while( echoValue == 0x00 && time < timeOut){
        //Delay for one microsecond so we can keep track of how much time it took to receive signal
        Clock_Delay1us(1);
        time++;
        echoValue = (P6->IN & echoBit);
    }

    time = 0;
    echoValue = (P6->IN & echoBit);

    //wait for echo signal to return to LOW
    while( echoValue != 0x00 && time < timeOut  ){
        //Delay for 1 microsecond and increment time variable so the time variable will store how much time it took for the echo signal to return to 0
        Clock_Delay1us(1);
        time++;
        echoValue = (P6->IN & echoBit);
    }

    //Rate of sound in air is approximately 0.0343 centimeters per microsecond
    //Distance = Rate * time
    distance = (0.0343 * time);

    return distance;
}

int objectDetected = 0;


void CheckDistance(void){

    distance = GetDistance(10000);
    uint8_t LED = 0x00;

    if(distance < 10){
        //If sensor detects an object, make the LED light RED
        LED = RED;

        //objectDetected is a global variable, and is referenced in the AvoidObject function
        objectDetected = 1;

    }else{
        //set LED to green if no object is in front
        LED = GREEN;

        objectDetected = 0;
    }

    //set LED's color
    LaunchPad_Output(LED);
}

void AvoidObject(void){

    //Turn on RED led on Robot
    LaunchPad_LED(0x01);

    //stop the motor
    Motor_Stop();
    Clock_Delay1ms(250);

    //Robot turns right when an object is detected
    Motor_Right(4000,4000);

    while(objectDetected == 1){
        //The robot will turn right until an object is no longer detected
    }

    //Stop motor when an object is no longer in front of the distance sensor
    Motor_Stop();

    //Turn off RED led
    LaunchPad_LED(0x00);

    //Wait for a short period of time before the function completes
    //This is not needed, however, I used it so the robot came to a short stop before continuing forward
    Clock_Delay1ms(500);
}

int main(void){

    Clock_Init48MHz();
    LaunchPad_Init(); // built-in switches and LEDs
    Motor_Init();     // your function
    Distance_Init();
    TimerA1_Init(&CheckDistance,50000);
    Clock_Delay1ms(1000);
    EnableInterrupts();

    while(1)
    {
        if(objectDetected == 0){
            Motor_Forward(5000,5000);
        }
        else{
            AvoidObject();
            Clock_Delay1ms(250);
        }
    }
}

#include <stdint.h>
#include "msp.h"
#include "../inc/Clock.h"
#include "../inc/CortexM.h"
#include "../inc/LaunchPad.h"
#include "../inc/Motor.h"
#include "../inc/TimerA1.h"

//Conected to P6.4
uint8_t trigBitMid = 0x10;

//Connected to P6.5
uint8_t echoBitMid = 0x20;

//Trigger pinL connected to P6.0
uint8_t trigBitLeft = 0x01;

//Echo pinL connected to P3.2
uint8_t echoBitLeft = 0x04;

//Trigger pinR connected to P4.1
uint8_t trigBitRight = 0x02;

//Echo pin R connected to P3.3
uint8_t echoBitRight = 0x08;

int distanceMid;
int distanceLeft;
int distanceRight;

int objectDetectedMid = 0;
int objectDetectedLeft = 0;
int objectDetectedRight = 0;


void Distance_Init(void){
    //Trigger as GPIO, P6.4
    P6->SEL0 &= ~trigBitMid;
    P6->SEL1 &= ~trigBitMid;
    //Trigger as Output
    P6->DIR |= trigBitMid;

    //Echo as GPIO P6.5
    P6->SEL0 &= ~echoBitMid;
    P6->SEL1 &= ~echoBitMid;
    //Echo as input
    P6->DIR &= ~echoBitMid;

    //TriggerL as GPIO P6.0
    P6->SEL0 &= ~trigBitLeft;
    P6->SEL1 &= ~trigBitLeft;
    //Trigger as Output
    P6->DIR |= trigBitLeft;

    //EchoBitL as GPIO P3.2
    P3->SEL0 &= ~echoBitLeft;
    P3->SEL1 &= ~echoBitLeft;
    //Echo as input
    P3->DIR &= ~echoBitLeft;

    //TriggerR as GPIO P4.1
    P4->SEL0 &= ~trigBitRight;
    P4->SEL1 &= ~trigBitRight;
    //Trigger as Output
    P4->DIR |= trigBitRight;

    //EchoBitR as GPIO P3.3
    P3->SEL0 &= ~echoBitRight;
    P3->SEL1 &= ~echoBitRight;
    //Echo as input
    P3->DIR &= ~echoBitRight;
}

void SetDistanceMid(int timeOut){
    //timeOut is a value in microseconds
    //it is used to exit the while loop if the signal is not found within the time limit

    int time;
    uint8_t echoValue;

    //Trigger off
    P6->OUT &= ~trigBitMid;
    Clock_Delay1us(2);

    //Trigger on
    P6->OUT |= trigBitMid;
    Clock_Delay1us(10);

    //Trigger off
    P6->OUT &= ~trigBitMid;

    time = 0;
    //Store the value of the echo sensor ANDing the pin vector with the bit that the echo sensor is connected to
    echoValue = (P6->IN & echoBitMid);

    //wait for triggers signal to be received by the echo sensor
    while( echoValue == 0x00 && time < timeOut){
        //Delay for one microsecond so we can keep track of how much time it took to receive signal
        Clock_Delay1us(1);
        time++;
        echoValue = (P6->IN & echoBitMid);
    }

    time = 0;
    echoValue = (P6->IN & echoBitMid);

    //wait for echo signal to return to LOW
    while( echoValue != 0x00 && time < timeOut  ){
        //Delay for 1 microsecond and increment time variable so the time variable will store how much time it took for the echo signal to return to 0
        Clock_Delay1us(1);
        time++;
        echoValue = (P6->IN & echoBitMid);
    }

    //Rate of sound in air is approximately 0.0343 centimeters per microsecond
    //Distance = Rate * time
    distanceMid = (0.0343 * time);
}

void SetDistanceLeft(int timeOut){
    //timeOut is a value in microseconds
    //it is used to exit the while loop if the signal is not found

    //Trigger Left connect to P6.0
    //Echo Left connect to P3.2

    int time;
    uint8_t echoValue;

    //Trigger off
    P6->OUT &= ~trigBitLeft;
    Clock_Delay1us(2);

    //Trigger on
    P6->OUT |= trigBitLeft;
    Clock_Delay1us(10);

    //Trigger off
    P6->OUT &= ~trigBitLeft;

    time = 0;
    //Store the value of the echo sensor ANDing the pin vector with the bit that the echo sensor is connected to
    echoValue = (P3->IN & echoBitLeft);

    //wait for triggers signal to be received by the echo sensor
    while( echoValue == 0x00 && time < timeOut){
        //Delay for one microsecond so we can keep track of how much time it took to receive signal
        Clock_Delay1us(1);
        time++;
        echoValue = (P3->IN & echoBitLeft);
    }

    time = 0;
    echoValue = (P3->IN & echoBitLeft);

    //wait for echo signal to return to LOW
    while( echoValue != 0x00 && time < timeOut  ){
        //Delay for 1 microsecond and increment time variable so the time variable will store how much time it took for the echo signal to return to 0
        Clock_Delay1us(1);
        time++;
        echoValue = (P3->IN & echoBitLeft);
    }

    //Rate of sound in air is approximately 0.0343 centimeters per microsecond
    //Distance = Rate * time
    distanceLeft = (0.0343 * time);
}


void SetDistanceRight(int timeOut){
    //timeOut is a value in microseconds
    //it is used to exit the while loop if the signal is not found

    //Trigger Right P4.1
    //Echo Right P3.3

    int time;
    uint8_t echoValue;

    //Trigger off
    P4->OUT &= ~trigBitRight;
    Clock_Delay1us(2);

    //Trigger on
    P4->OUT |= trigBitRight;
    Clock_Delay1us(10);

    //Trigger off
    P4->OUT &= ~trigBitRight;

    time = 0;
    //Store the value of the echo sensor ANDing the pin vector with the bit that the eacho sensor is connected to
    echoValue = (P3->IN & echoBitRight);

    //wait for triggers signal to be received by the echo sensor
    while( echoValue == 0x00 && time < timeOut){
        //Delay for one microsecond so we can keep track of how much time it took to receive signal
        Clock_Delay1us(1);
        time++;
        echoValue = (P3->IN & echoBitRight);
    }

    time = 0;
    echoValue = (P3->IN & echoBitRight);

    //wait for echo signal to return to LOW
    while( echoValue != 0x00 && time < timeOut  ){
        //Delay for 1 microsecond and increment time variable so the time variable will store how much time it took for the echo signal to return to 0
        Clock_Delay1us(1);
        time++;
        echoValue = (P3->IN & echoBitRight);
    }

    //Rate of sound in air is approximately 0.0343 centimeters per microsecond
    //Distance = Rate * time
    distanceRight = (0.0343 * time);
}


void CheckDistance(void){

    //Look for distance for a max of 1 second
    SetDistanceMid(1000);
    SetDistanceLeft(1000);
    SetDistanceRight(1000);

    uint8_t LED = 0x00;

    if(distanceMid < 15){
        //You can change the value in the if statement to whatever you would like

        //If an object is closer than 10cm in the middle...
        //make the LED light RED
        LED = RED;

        //objectDetectedMid is a global variable, and is referenced in the AvoidObject function
        objectDetectedMid = 1;

    }else{
        //set LED to green if no object is in front
        LED = GREEN;

        objectDetectedMid = 0;
    }

    if(distanceLeft < 10){
        //If an object is closer than 6cm on the left...
        //make the LED light yellow
        LED = 0x03;
        objectDetectedLeft = 1;

    }else{

        objectDetectedLeft = 0;
    }

    if(distanceRight < 10){
        //If an object is closer than 6cm on the right...
        //make the LED light blue
        LED = 0x04;
        objectDetectedRight = 1;

    }else{

        objectDetectedRight = 0;
    }

    //set LED's color
    LaunchPad_Output(LED);
}

void AvoidObjectMid(void){

    //Turn on RED led on Robot
    LaunchPad_LED(0x01);
	
    Motor_Stop();
    Clock_Delay1ms(250);

    if(distanceLeft < distanceRight){
        //If an object is closer on the left side, then robot turns right
        Motor_Right(4000,4000);
    }else{
        //If object is closer on the right side, then robot turns left
        Motor_Left(4000,4000);
    }


    while(objectDetectedMid == 1){
        //The robot will turn right until an object is no longer detected
    }

    //Stop motor when an object is no longer in front of the distance sensor
    Motor_Stop();

    //Turn off RED led
    LaunchPad_LED(0x00);

    //Wait for a short period of time before the function completes
    //This is not needed, however, I used it so the robot came to a short stop before continuing forward
    Clock_Delay1ms(500);
}


void AvoidObjectLeft(void){

    //Turn on RED led on Robot
    LaunchPad_LED(0x01);

    Motor_Stop();
    Clock_Delay1ms(250);

    //Robot turns right when an object is detected on left
    Motor_Right(4000,4000);

    while(objectDetectedLeft == 1){
        //The robot will turn right until an object is no longer detected
    }

    //Stop motor when an object is no longer in front of the distance sensor
    Motor_Stop();

    //Turn off RED led
    LaunchPad_LED(0x00);

    //Wait for a short period of time before the function completes
    //This is not needed, however, I used it so the robot came to a short stop before continuing forward
    Clock_Delay1ms(500);
}

void AvoidObjectRight(void){

    //Turn on RED led on Robot
    LaunchPad_LED(0x01);
	
    Motor_Stop();
    Clock_Delay1ms(250);

    //Robot turns left when an object is detected on right
    Motor_Left(4000,4000);

    while(objectDetectedRight == 1){
        //The robot will turn left until an object is no longer detected
    }

    //Stop motor when an object is no longer in front of the distance sensor
    Motor_Stop();

    //Turn off RED led
    LaunchPad_LED(0x00);

    //Wait for a short period of time before the function completes
    //This is not needed, however, I used it so the robot came to a short stop before continuing forward
    Clock_Delay1ms(500);
}

int main(void){

    Clock_Init48MHz();
    LaunchPad_Init();
    Motor_Init();
    Distance_Init();
    TimerA1_Init(&CheckDistance,50000);
    Clock_Delay1ms(1000);
    EnableInterrupts();

    while(1)
    {
        //objectDetected variable is changed in the CheckDistance function
        if(objectDetectedMid == 1){
            AvoidObjectMid();
            Clock_Delay1ms(250);
        }
        else if(objectDetectedLeft == 1){
            AvoidObjectLeft();
            Clock_Delay1ms(250);
        }
        else if(objectDetectedRight == 1){
            AvoidObjectRight();
            Clock_Delay1ms(250);
        }else{
            Motor_Forward(5000,5000);
        }
    }
}

Credits

Contact

Thanks to Quoc-Viet Dang.

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Texas Instruments RSLK with Ultrasonic Distance Sensors