Project showcase
Control Arduino LittleArm with Ultrasonic Sensor

Control Arduino LittleArm with Ultrasonic Sensor © CC BY-NC-SA

Use an Ultrasonic sensor to control the vertical height of the LittleArm.

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Components and supplies

About this project

This is the first step of creating a 3D controller to be used with the LittleArm. Eventually we will create a rig that tracks two hands in order to control the Littlearm in 3D.

This project is meant to give a basic introduction to using the ultrasonic sensor with some new hardware that we have started using.


The main new piece is the Meped board. The board allows you to quickly add sensors without having to mess with a bunch of wiring diagrams. It is basically plug-and-play so you can focus on programming.

The code is actually pretty simple. We just the standard LittleArm firmware to work with an Arduino Nano and then added in a check on the ultrasonic sensor if no serial commands were available.

The only part of the code that might need to be different from one arm to the next is the range of the sensor and of the joint angles. Based on how the kit was put together, the optimum values may be different.

 if ((readDistance > 3 )&& (readDistance < 30)){ 
    //move the elbow and shoulder some amount 
    desiredAngle.elbow = map(readDistance, 5, 30, 175, 70); 
    desiredAngle.shoulder = map(readDistance, 5, 30, 5, 100); 
    desiredAngle.base = 90; 

This is a very basic demo. But as said before, this will be expanded with another sensor soon to allow the arm to be moved from side to side as well as up and down. Then if we replace the gripper with a hook, it could be a pretty cool robot.


LittleArm Ultrasonic Code 1Arduino
#include <Servo.h>  //arduino library
#include <math.h>   //standard c library

#define PI 3.141

Servo baseServo;  
Servo shoulderServo;  
Servo elbowServo; 
Servo gripperServo;

struct jointAngle{
  int base;
  int shoulder;
  int elbow;

struct jointAngle desiredAngle; //desired angles of the servos

int desiredGrip;
int gripperPos;
int command;
int desiredDelay = 16;

int ready = 0;

//+++++++++++++++ULTRASONIC VARIABLES++++++++++++++++++++++++++++

#define echoPin A2 // Echo Pin
#define trigPin A3 // Trigger Pin

bool holder = 1;
int maximumRange = 200; // Maximum range needed
int minimumRange = 0; // Minimum range needed
long readDistance; // the output distance from the sensor

//+++++++++++++++FUNCTION DECLARATIONS+++++++++++++++++++++++++++
int servoParallelControl (int thePos, Servo theServo );
int ultraSensor(int theEchoPin, int theTrigPin);

void setup()
  baseServo.attach(5);        // attaches the servo on pin 5 to the servo object 
  Serial.setTimeout(50);      //ensures the the arduino does not read serial for too long
  baseServo.write(90);        //intial positions of servos
  ready = 0;

   pinMode(trigPin, OUTPUT);
   pinMode(echoPin, INPUT);

//primary arduino loop
void loop() 

  // read a usb command if available
  if (Serial.available()){
    ready = 1;
    desiredAngle.base = Serial.parseInt();
    desiredAngle.shoulder = Serial.parseInt();
    desiredAngle.elbow = Serial.parseInt();
    desiredGrip = Serial.parseInt();
    desiredDelay = Serial.parseInt();

    if( == '\n'){              // if the last byte is 'd' then stop reading and execute command 'd' stands for 'done'
        Serial.flush();                     //clear all other commands piled in the buffer
        Serial.print('d');                  //send completion of the command
   //read the distance read by the sensor
   desiredDelay = 3;
   readDistance = ultraSensor(echoPin, trigPin);
   ready = 1;
   if ((readDistance > 3 )&& (readDistance < 30)){
      //move the elbow and shoulder some amount
      desiredAngle.elbow = map(readDistance, 5, 30, 175, 70);
      desiredAngle.shoulder = map(readDistance, 5, 30, 5, 100);
      desiredAngle.base = 90;
  } // end of ultrasonic else
  int status1 = 0;
  int status2 = 0;
  int status3 = 0;
  int status4 = 0;
  int done = 0 ; 
  while(done == 0 && ready == 1){  
    //move the servo to the desired position
    status1 = servoParallelControl(desiredAngle.base, baseServo, desiredDelay);
    status2 = servoParallelControl(desiredAngle.shoulder,  shoulderServo, desiredDelay);
    status3 = servoParallelControl(desiredAngle.elbow, elbowServo, desiredDelay);      
    status4 = servoParallelControl(desiredGrip, gripperServo, desiredDelay);  
    if (status1 == 1 & status2 == 1 & status3 == 1 & status4 == 1){
      done = 1;
  }// end of while

//++++++++++++++++++++++++++++++FUNCTION DEFINITIONS++++++++++++++++++++++++++++++++++++++++++

int servoParallelControl (int thePos, Servo theServo, int theSpeed ){
    int startPos =;        //read the current pos
    int newPos = startPos;
    //int theSpeed = speed;
    //define where the pos is with respect to the command
    // if the current position is less that the actual move up
    if (startPos < (thePos-5)){
       newPos = newPos + 1;
       return 0;
   else if (newPos > (thePos + 5)){
      newPos = newPos - 1;
      return 0;
    else {
        return 1;
} //end servo parallel control


int ultraSensor(int theEchoPin, int theTrigPin){
   //this fucntion caluclates and returns the distance in cm
   long duration, distance; // Duration used to calculate distance
   /* The following trigPin/echoPin cycle is used to determine the
   distance of the nearest object by bouncing soundwaves off of it. */ 
   digitalWrite(theTrigPin, LOW); 
   digitalWrite(theTrigPin, HIGH);
   digitalWrite(theTrigPin, LOW);
   duration = pulseIn(theEchoPin, HIGH);
   //Calculate the distance (in cm) based on the speed of sound.
   distance = duration/58.2;  
   return distance;


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