电子发烧友网>电子资料下载>电子资料>带Arduino的四足蜘蛛机器人

带Arduino的四足蜘蛛机器人

2077293 2023-02-08 | zip | 3.33 MB | 次下载 | 2积分

普通下载普通下载

资料介绍

描述

第 1 步：调整伺服电机位置

1 / 2 •调整伺服

在开始组装之前，我们需要手动调整伺服电机的角度调整。否则，您的机器人将无法正常工作。

将伺服臂连接到伺服器上，然后顺时针缓慢转动伺服臂，直到臂停止。如果伺服臂没有停止在上图所示的相同角度，那也没关系。重要的是我们找到伺服的终点。从伺服器上拆下伺服臂并重新定位，使其垂直于伺服器主体。

如图所示，慢慢逆时针转动舵机臂，直到它与舵机本体平行。这是伺服系统的中心位置，在开始组装机器人之前，将 8 个伺服系统置于中心位置非常重要。舵机臂与舵机本体平行后，取下舵机臂，放置一旁待用。

校准舵机

如果您的伺服电机是 360 度模拟伺服电机，则无法进行手动布线。这就是为什么您可以使用我与您分享的代码来校准您的伺服电机。如上面（3）的电路图，把你的伺服电机变成1.2.3.4.5.6.7.8。将底部的代码连接到引脚，将其安装到您的 arduino。如果不这样做，您的机器人将无法稳定工作。

伺服校准代码：

#include     // include servo library


// Define 8 Servos
Servo myServo1; // Front Left Pivot Servo
Servo myServo2; // Front Left Lift Servo
Servo myServo3; // Back Left Pivot Servo
Servo myServo4; // Back Left Lift Servo
Servo myServo5; // Back Right Pivot Servo
Servo myServo6; // Back Right Lift Servo
Servo myServo7; // Front Right Pivot Servo
Servo myServo8; // Front Right Lift Servo


void setup() {
  // put your setup code here, to run once:
  myServo1.attach(1);
  myServo2.attach(2);
  myServo3.attach(3);
  myServo4.attach(4);
  myServo5.attach(5);
  myServo6.attach(6);
  myServo7.attach(7);
  myServo8.attach(8);
  
  myServo1.write(90);
  myServo2.write(90);
  myServo3.write(90);
  myServo4.write(90);
  myServo5.write(90);
  myServo6.write(90);
  myServo7.write(90);
  myServo8.write(90);
}


void loop() {
  
  // put your main code here, to run repeatedly:
}

如果您已完成伺服调整，则可以进入腿部组装阶段。

第 2 步：腿组装阶段

1 / 3 •支腿组装

您必须按照逐步的视觉效果来连接腿部。您可以按照原理图中的步骤名称进行连接。重复步骤 1 到 10 恰好4 次并构建 4 条腿：

第 1 步：将伺服单臂放在底座枢轴板上，然后将伺服安装螺钉从支腿向上枢轴板的后部拧入伺服单臂。
第 2 步：将伺服单臂连接到站立式伺服臂，并将伺服安装螺钉连接到伺服。从腿部伺服臂的背面拧上伺服单臂。
第 3 步：使用 M3x10mm 螺钉和 M3 纤维螺母将腿部平行接头连接到腿部部件。
第 4 步：使用 M3X10mm 螺钉和 M3 纤维螺母将支腿连接到支腿伺服臂。
第 5 步：将伺服器插入伺服器支架。
第 6 步：将伺服器的顶端插入基座伺服器槽中。
第 7 步：使用两个 M3 x 12mm 螺钉和两个 M3 纤维螺母将伺服支架连接到支腿伺服插座。
第 8 步：使用 M3X10MM 螺钉和 M3 纤维螺母将腿平行板连接到腿的另一端。
第 9 步：将舵机旋转到中心位置，腿部平行关节水平放置，使用舵机随附的舵机臂螺钉将腿部舵机臂连接到舵机上
第 10 步：使用两个 M3 x 10mm 螺丝和两个 M3 螺母将前面步骤中的腿组件连接到腿底部枢轴板。

腿组装有点困难，但相信我，如果这些阶段结束了，剩下的就来了。如果您已完成这些步骤，让我们继续进行车身组装部分。

第 3 步：车身组装

1 / 2 •车身装配 - 方案 1 和 2

在这个阶段，你应该小心数字。原理图是根据零件号解释的，因此您应该在组装之前阅读我们创建的列表；

架构 1 和 2 的零件清单：

1- 车身上板
2- M3x10MM 螺丝
3 - 伺服电机
4 - M3 螺母
5 - M3 纤维螺母
7 - M3x12MM 螺丝
8 - 垫片
10 - 伺服支架

第 11 步：使用四个 M3x10mm 螺钉和四个 M3 平螺母将四个阀杆垫片连接到阀杆底板上。

第 12 步：将四个舵机放在机箱顶板的顶部。

第 13 步：将舵机支架连接到每个舵机的顶部。

第 14 步：使用 M3x12mm 螺钉和 M3 纤维螺母将每个伺服支架连接到机箱顶板。

1 / 3 •车身组装 - 方案 3、4 和 5

模式 3、4 和 5 的零件清单：

1 - 伺服螺丝
2 - M3x10MM 螺栓
3 - M3 螺母
4 - M3 纤维螺母

第 15 步：使用 M3x10mm 螺钉和 M3 纤维螺母将每个支腿连接到杆底板上。不要将螺钉拧得过紧，否则可能会导致舵机发生故障。

第 16 步：使用四块 M3x10mm 螺钉和 M3 螺母将主体底板连接到主体顶板。

第 17 步：旋转每条腿，使其呈 45 度角，如图所示。安装支腿上枢轴板。使用两个 M3x10mm 螺钉和两个 M3 螺母安装到每个枢轴伺服器和支腿。

Step 18：用舵机螺丝将舵机单臂固定到舵机上。

最后，使用树脂立管将电池座固定在机器人的下部。

第 4 步：Arduino 连接

Arduino 连接

是时候在 Arduino 和组件之间建立连接了。

请按照说明进行操作：

左前轴：引脚 2
左前提升：引脚 3
左后轴：引脚 4
左后提升：引脚 5
右后轴：引脚 6
右后提升：引脚 7
右前轴：引脚 8
右前提升：引脚 9
红外模块：引脚 12

如电路图所示，从第 2 个数字引脚到第 9 个数字引脚按顺序连接伺服电机。如图所示，将IR 接收器模块连接到第 12 个引脚。

1 / 2 •用于屏蔽的外部电源连接

由于蜘蛛机器人使用多个伺服电机，arduon的功率不足，为此我们需要进行外部电源输入。

您需要使用最小 4.8v 最大 5v 电源为 shild 供电。无论使用锂电池还是经典电池，都取决于您将提供什么样的能量。

这里重要的是它不能超过 5 伏特，否则你的 Arduino 会损坏。我已经与您分享了一些电池样本（第二张图片）作为示例。如果要在上面使用锂聚合物电池，则必须使用侧面的降压电路。因为大于 5 伏的电压会损坏您的卡。

如电路图（第三张图）所示，将降压电路的输出设置为 5 伏并将其连接到屏蔽层就足够了。

可选 AAA 电池连接

此外，您可以改用经典的 AAA 电池。为此，您应该将 4 节 AAA 电池插入电池座，然后连接到 Arduino 扩展板。

第 5 步：上传 Arduino 代码和结论

我们已经为您准备了一个代码，以便您一开始就可以毫无问题地移动蜘蛛机器人。代码中准备了一些命令，但你可以自己修改它；

#include  // include IR Remote library
#include     // include servo library


//===== Globals ============================================================================


// Define USRF pins and variables
#define trigPin A3
#define echoPin A2
#define INCH 0
#define CM 1


// Define IR Remote Button Codes
#define irUp  16736925
#define irDown 16754775
#define irRight 16761405
#define irLeft 16720605
#define irOK 16712445
#define ir1 16738455
#define ir2 16750695
#define ir3 16756815
#define ir4 16724175
#define ir5 16718055
#define ir6 16743045
#define ir7 16716015
#define ir8 16726215
#define ir9 16734885
#define ir0 16730805
#define irStar 16728765
#define irPound 0000005
#define irRepeat 16732845



// calibration
int da =  -12,  // Left Front Pivot
    db =   10,  // Left Back Pivot
    dc =  -18,  // Right Back Pivot
    dd =   12;  // Right Front Pivot


// servo initial positions + calibration
int a90  = (90  + da),
    a120 = (120 + da),
    a150 = (150 + da),
    a180 = (180 + da);


int b0   = (0   + db),
    b30  = (30  + db),
    b60  = (60  + db),
    b90  = (90  + db);


int c90  = (90  + dc),
    c120 = (120 + dc),
    c150 = (150 + dc),
    c180 = (180 + dc);


int d0   = (0   + dd),
    d30  = (30  + dd),
    d60  = (60  + dd),
    d90  = (90  + dd);


// start points for servo
int s11 = 90; // Front Left Pivot Servo
int s12 = 90; // Front Left Lift Servo
int s21 = 90; // Back Left Pivot Servo
int s22 = 90; // Back Left Lift Servo
int s31 = 90; // Back Right Pivot Servo
int s32 = 90; // Back Right Lift Servo
int s41 = 90; // Front Right Pivot Servo
int s42 = 90; // Front Right Lift Servo


int f    = 0;
int b    = 0;
int l    = 0;
int r    = 0;
int spd  = 3;  // Speed of walking motion, larger the number, the slower the speed
int high = 0;   // How high the robot is standing


// Define 8 Servos
Servo myServo1; // Front Left Pivot Servo
Servo myServo2; // Front Left Lift Servo
Servo myServo3; // Back Left Pivot Servo
Servo myServo4; // Back Left Lift Servo
Servo myServo5; // Back Right Pivot Servo
Servo myServo6; // Back Right Lift Servo
Servo myServo7; // Front Right Pivot Servo
Servo myServo8; // Front Right Lift Servo


// Set up IR Sensor
int irReceiver = 12;       // Use pin D12 for IR Sensor
IRrecv irrecv(irReceiver); // create a new instance of the IR Receiver
decode_results results;


//==========================================================================================


//===== Setup ==============================================================================


void setup()
{
  // Attach servos to Arduino Pins
  myServo1.attach(2);
  myServo2.attach(3);
  myServo3.attach(4);
  myServo4.attach(5);
  myServo5.attach(6);
  myServo6.attach(7);
  myServo7.attach(8);
  myServo8.attach(9);


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


  irrecv.enableIRIn(); //start the receiver


  Serial.begin (9600);


}//setup


//==========================================================================================


//== Loop ==================================================================================


void loop()
{
  unsigned long value;
  unsigned long lastValue;
  
  center_servos();  // Center all servos
  high = 15;        // Set hight to 15
  spd = 3;          // Set speed to 3


  while (1 == 1)    // Loop forever
  {
    if (irrecv.decode(&results)) // If we have received an IR signal
    {
      value = results.value;


      if (value == irRepeat)
        value = lastValue;


      switch (value)
      {
        case irUp:
          lastValue = irUp;
          forward();
          break;


        case irDown:
          lastValue = irDown;
          back();
          break;


        case irRight:
          lastValue = irRight;
          turn_right();
          break;


        case irLeft:
          lastValue = irLeft;
          turn_left();
          break;


        case irOK:
          lastValue = irOK;
          break;


        case ir1:
          lastValue = ir1;
          bow();
          break;


        case ir2:
          lastValue = ir2;
          wave();
          break;


        case ir3:
          lastValue = ir3;
          increase_speed();
          break;


        case ir4:
          lastValue = ir4;
          break;


        case ir5:
          lastValue = ir5;
          break;


        case ir6:
          lastValue = ir6;
          decrease_speed();
          break;


        case ir7:
          lastValue = ir7;
          break;


        case ir8:
          lastValue = ir8;
          dance();
          break;


        case ir9:
          lastValue = ir9;
          break;


        case ir0:
          lastValue = ir0;
          center_servos();
          break;


        case irStar:
          lastValue = irStar;
          trim_left();
          break;


        case irPound:
          lastValue = irPound;
          trim_right();
          break;


        default:
          break;
      }


      irrecv.resume(); //next value
      delay(50);  // Pause for 50ms before executing next movement


    }// if irrecv.decode
  }//while


}//loop


void dance()
{
  center_servos();
  delay(100);
  lean_left();
  delay(300);
  lean_right();
  delay(300);
  lean_left();
  delay(300);
  lean_right();
  delay(300);
  lean_left();
  delay(300);
  lean_right();
  delay(300);
  lean_left();
  delay(300);
  lean_right();
  delay(800);
  center_servos();
  delay(300);
  bow();
  center_servos();
}


//== Wave ==================================================================================


void wave()
{
  /*
  myServo1 - Front Left Pivot Servo
  myServo2 - Front Left Lift Servo
  myServo3 - Back Left Pivot Servo
  myServo4 - Back Left Lift Servo
  myServo5 - Back Right Pivot Servo
  myServo6 - Back Right Lift Servo
  myServo7 - Front Right Pivot Servo
  myServo8 - Front Right Lift Servo
  */


  center_servos();
  myServo4.write(45);
  myServo6.write(45);
  delay(200);
  myServo8.write(0);
  delay(200);
  myServo7.write(180);
  delay(200);
  myServo7.write(30);
  delay(300);
  myServo7.write(180);
  delay(300);
  myServo7.write(30);
  delay(300);
  myServo7.write(s41);
  delay(300);
  myServo8.write(s42);
  center_servos();


}


//== Bow ===================================================================================


void bow()
{
  center_servos();
  delay(200);
  myServo2.write(15);
  myServo8.write(15);
  delay(700);
  myServo2.write(90);
  myServo8.write(90);
  delay(700);
}


//== Lean_Left =============================================================================


void lean_left()
{
  myServo2.write(15);
  myServo4.write(15);
  myServo6.write(150);
  myServo8.write(150);
}


//== Lean_Right ============================================================================


void lean_right()
{
  myServo2.write(150);
  myServo4.write(150);
  myServo6.write(15);
  myServo8.write(15);
}


//== Lean_Left =============================================================================


void trim_left()
{
  da--; // Left Front Pivot
  db--; // Left Back Pivot
  dc--; // Right Back Pivot
  dd--; // Right Front Pivot
}


//== Lean_Right ============================================================================


void trim_right()
{
  da++; // Left Front Pivot
  db++; // Left Back Pivot
  dc++; // Right Back Pivot
  dd++; // Right Front Pivot
}


//== Forward ===============================================================================


void forward()
{
  // calculation of points


  // Left Front Pivot
  a90 = (90 + da),
  a120 = (120 + da),
  a150 = (150 + da),
  a180 = (180 + da);


  // Left Back Pivot
  b0 = (0 + db),
  b30 = (30 + db),
  b60 = (60 + db),
  b90 = (90 + db);


  // Right Back Pivot
  c90 = (90 + dc),
  c120 = (120 + dc),
  c150 = (150 + dc),
  c180 = (180 + dc);


  // Right Front Pivot
  d0 = (0 + dd),
  d30 = (30 + dd),
  d60 = (60 + dd),
  d90 = (90 + dd);


  // set servo positions and speeds needed to walk forward one step
  // (LFP,  LBP, RBP,  RFP, LFL, LBL, RBL, RFL, S1, S2, S3, S4)
  srv(a180, b0 , c120, d60, 42,  33,  33,  42,  1,  3,  1,  1);
  srv( a90, b30, c90,  d30, 6,   33,  33,  42,  3,  1,  1,  1);
  srv( a90, b30, c90,  d30, 42,  33,  33,  42,  3,  1,  1,  1);
  srv(a120, b60, c180, d0,  42,  33,  6,   42,  1,  1,  3,  1);
  srv(a120, b60, c180, d0,  42,  33,  33,  42,  1,  1,  3,  1);
  srv(a150, b90, c150, d90, 42,  33,  33,  6,   1,  1,  1,  3);
  srv(a150, b90, c150, d90, 42,  33,  33,  42,  1,  1,  1,  3);
  srv(a180, b0,  c120, d60, 42,  6,   33,  42,  1,  3,  1,  1);
  //srv(a180, b0,  c120, d60, 42,  15,  33,  42,  1,  3,  1,  1);
  
}


//== Back ==================================================================================


void back ()
{
  // set servo positions and speeds needed to walk backward one step
  // (LFP,  LBP, RBP,  RFP, LFL, LBL, RBL, RFL, S1, S2, S3, S4)
  srv(180, 0,  120, 60, 42, 33, 33, 42, 3,  1, 1, 1);
  srv(150, 90, 150, 90, 42, 18, 33, 42, 1,  3, 1, 1);
  srv(150, 90, 150, 90, 42, 33, 33, 42, 1,  3, 1, 1);
  srv(120, 60, 180, 0,  42, 33, 33, 6,  1,  1, 1, 3);
  srv(120, 60, 180, 0,  42, 33, 33, 42, 1,  1, 1, 3);
  srv(90,  30, 90,  30, 42, 33, 18, 42, 1,  1, 3, 1);
  srv(90,  30, 90,  30, 42, 33, 33, 42, 1,  1, 3, 1);
  srv(180, 0,  120, 60, 6,  33, 33, 42, 3,  1, 1, 1);


}


//== Left =================================================================================


void turn_left ()
{
  // set servo positions and speeds needed to turn left one step
  // (LFP,  LBP, RBP,  RFP, LFL, LBL, RBL, RFL, S1, S2, S3, S4)
  srv(150,  90, 90,  30, 42, 6,  33, 42, 1, 3, 1, 1);
  srv(150,  90, 90,  30, 42, 33, 33, 42, 1, 3, 1, 1);
  srv(120,  60, 180, 0,  42, 33, 6,  42, 1, 1, 3, 1);
  srv(120,  60, 180, 0,  42, 33, 33, 24, 1, 1, 3, 1);
  srv(90,   30, 150, 90, 42, 33, 33, 6,  1, 1, 1, 3);
  srv(90,   30, 150, 90, 42, 33, 33, 42, 1, 1, 1, 3);
  srv(180,  0,  120, 60, 6,  33, 33, 42, 3, 1, 1, 1);
  srv(180,  0,  120, 60, 42, 33, 33, 33, 3, 1, 1, 1);
}


//== Right ================================================================================


void turn_right ()
{
  // set servo positions and speeds needed to turn right one step
  // (LFP,  LBP, RBP,  RFP, LFL, LBL, RBL, RFL, S1, S2, S3, S4)
  srv( 90, 30, 150, 90, 6,  33, 33, 42, 3, 1, 1, 1);
  srv( 90, 30, 150, 90, 42, 33, 33, 42, 3, 1, 1, 1);
  srv(120, 60, 180, 0,  42, 33, 33, 6,  1, 1, 1, 3);
  srv(120, 60, 180, 0,  42, 33, 33, 42, 1, 1, 1, 3);
  srv(150, 90, 90,  30, 42, 33, 6,  42, 1, 1, 3, 1);
  srv(150, 90, 90,  30, 42, 33, 33, 42, 1, 1, 3, 1);
  srv(180, 0,  120, 60, 42, 6,  33, 42, 1, 3, 1, 1);
  srv(180, 0,  120, 60, 42, 33, 33, 42, 1, 3, 1, 1);
}


//== Center Servos ========================================================================


void center_servos()
{
  myServo1.write(90);
  myServo2.write(90);
  myServo3.write(90);
  myServo4.write(90);
  myServo5.write(90);
  myServo6.write(90);
  myServo7.write(90);
  myServo8.write(90);


  int s11 = 90; // Front Left Pivot Servo
  int s12 = 90; // Front Left Lift Servo
  int s21 = 90; // Back Left Pivot Servo
  int s22 = 90; // Back Left Lift Servo
  int s31 = 90; // Back Right Pivot Servo
  int s32 = 90; // Back Right Lift Servo
  int s41 = 90; // Front Right Pivot Servo
  int s42 = 90; // Front Right Lift Servo
}


//== Increase Speed ========================================================================


void increase_speed()
{
  if (spd > 3)
    spd--;
}


//== Decrease Speed ========================================================================


void decrease_speed()
{
  if (spd < 50)
    spd++;
}


//== Srv ===================================================================================


void srv( int  p11, int p21, int p31, int p41, int p12, int p22, int p32, int p42, int sp1, int sp2, int sp3, int sp4)
{


  // p11: Front Left Pivot Servo
  // p21: Back Left Pivot Servo
  // p31: Back Right Pivot Servo
  // p41: Front Right Pivot Servo
  // p12: Front Left Lift Servo
  // p22: Back Left Lift Servo
  // p32: Back Right Lift Servo
  // p42: Front Right Lift Servo
  // sp1: Speed 1
  // sp2: Speed 2
  // sp3: Speed 3
  // sp4: Speed 4


  // Multiply lift servo positions by manual height adjustment
  p12 = p12 + high * 3;
  p22 = p22 + high * 3;
  p32 = p32 + high * 3;
  p42 = p42 + high * 3;


  while ((s11 != p11) || (s21 != p21) || (s31 != p31) || (s41 != p41) || (s12 != p12) || (s22 != p22) || (s32 != p32) || (s42 != p42))
  {


    // Front Left Pivot Servo
    if (s11 < p11)            // if servo position is less than programmed position
    {
      if ((s11 + sp1) <= p11)
        s11 = s11 + sp1;      // set servo position equal to servo position plus speed constant
      else
        s11 = p11;
    }


    if (s11 > p11)            // if servo position is greater than programmed position
    {
      if ((s11 - sp1) >= p11)
        s11 = s11 - sp1;      // set servo position equal to servo position minus speed constant
      else
        s11 = p11;
    }


    // Back Left Pivot Servo
    if (s21 < p21)
    {
      if ((s21 + sp2) <= p21)
        s21 = s21 + sp2;
      else
        s21 = p21;
    }


    if (s21 > p21)
    {
      if ((s21 - sp2) >= p21)
        s21 = s21 - sp2;
      else
        s21 = p21;
    }


    // Back Right Pivot Servo
    if (s31 < p31)
    {
      if ((s31 + sp3) <= p31)
        s31 = s31 + sp3;
      else
        s31 = p31;
    }


    if (s31 > p31)
    {
      if ((s31 - sp3) >= p31)
        s31 = s31 - sp3;
      else
        s31 = p31;
    }


    // Front Right Pivot Servo
    if (s41 < p41)
    {
      if ((s41 + sp4) <= p41)
        s41 = s41 + sp4;
      else
        s41 = p41;
    }


    if (s41 > p41)
    {
      if ((s41 - sp4) >= p41)
        s41 = s41 - sp4;
      else
        s41 = p41;
    }


    // Front Left Lift Servo
    if (s12 < p12)
    {
      if ((s12 + sp1) <= p12)
        s12 = s12 + sp1;
      else
        s12 = p12;
    }


    if (s12 > p12)
    {
      if ((s12 - sp1) >= p12)
        s12 = s12 - sp1;
      else
        s12 = p12;
    }


    // Back Left Lift Servo
    if (s22 < p22)
    {
      if ((s22 + sp2) <= p22)
        s22 = s22 + sp2;
      else
        s22 = p22;
    }


    if (s22 > p22)
    {
      if ((s22 - sp2) >= p22)
        s22 = s22 - sp2;
      else
        s22 = p22;
    }


    // Back Right Lift Servo
    if (s32 < p32)
    {
      if ((s32 + sp3) <= p32)
        s32 = s32 + sp3;
      else
        s32 = p32;
    }


    if (s32 > p32)
    {
      if ((s32 - sp3) >= p32)
        s32 = s32 - sp3;
      else
        s32 = p32;
    }


    // Front Right Lift Servo
    if (s42 < p42)
    {
      if ((s42 + sp4) <= p42)
        s42 = s42 + sp4;
      else
        s42 = p42;
    }


    if (s42 > p42)
    {
      if ((s42 - sp4) >= p42)
        s42 = s42 - sp4;
      else
        s42 = p42;
    }


    // Write Pivot Servo Values
    myServo1.write(s11 + da);
    myServo3.write(s21 + db);
    myServo5.write(s31 + dc);
    myServo7.write(s41 + dd);


    // Write Lift Servos Values
    myServo2.write(s12);
    myServo4.write(s22);
    myServo6.write(s32);
    myServo8.write(s42);


    delay(spd); // Delay before next movement


  }//while
} //srv


//== USRF Function ========================================================================


long get_distance(bool unit)
{
  // if unit == 0 return inches, else return cm


  long duration = 0, 
       cm = 0, 
       inches = 0;


  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  digitalWrite(trigPin, LOW);
  delayMicroseconds(5);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);


  // Read the signal from the sensor: a HIGH pulse whose
  // duration is the time (in microseconds) from the sending
  // of the ping to the reception of its echo off of an object.
  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);


  // convert the time into a distance
  cm = (duration / 2) / 29.1;
  inches = (duration / 2) / 74;


  if (unit == INCH)
    return inches;
  else
    return cm;
}