Day 6: Analog Sensors | Functions and Modularity

Functions

Functions are sets of statements that typically perform operation or compute value. They can help to make programs more accessible and usable for non-programmers e.g. create function that allows user to type "go forward" and move a robot forward.

Modules

-Functions can be split up into modules, "divide and conquer"
-Each module has specific purpose, can be written and tested separately
-Smaller than complete solution, therefore testing is easier
-Can be used in new problem solutions without being retested
-Reduces overall length of program
-Allows for increased collaboration; modules can be worked on in parallel

Debugging Longer Programs

Use a compiler that gives meaningful information about errors. Adding comments around some sections of code can allow for better focus on other parts of the program. Test complicated functions by themselves.

Programmer Defined Functions

Execution of program always begins with main function. Additional functions are called when program encounters function names.

Example 1.1
/* */
/* This program prints 21 values of the sinc */
/* function in the interval [a,b] using */
/* computations within the main function. */
#include <stdio.h>
#include <math.h>
#define PI 3.141593
int main(void)
{
/* Declare variables. */
int k;
double a, b, x_incr, new_x, sinc_x;
/* Get interval endpoints from the user. */
printf("Enter endpoints a and b (a<b): \n");
scanf("%lf %lf",&a,&b);
x_incr = (b - a)/20;
/* Compute and print table of sinc(x) values. */
printf("x and sinc(x) \n");
for (k=0; k<=20; k++)
{
new_x = a + k*x_incr;
if (fabs(new_x) < 0.0001)
sinc_x = 1.0;
else
sinc_x = sin(PI*new_x)/(PI*new_x);
printf("%f %f \n",new_x,sinc_x);
}
/* Exit program. */
return 0;
}

Example 1.2
/* This program prints 21 values of the sinc function */
/* using a programmer-defined function. */
#include <stdio.h>
#include <math.h>
#define PI 3.141593
int main(void)
{
/* Declare variables. */
int k;
double a, b, x_incr, new_x;
double sinc(double x);
/* Get interval endpoints from the user. */
printf("Enter endpoints a and b (a<b): \n");
scanf("%lf %lf",&a,&b);
x_incr = (b - a)/20;
/* Compute and print table of sinc(x) values. */
printf("x and sinc(x) \n");
for (k=0; k<=20; k++)
{
new_x = a + k*x_incr;
printf("%f %f \n",new_x,sinc(new_x));
}
/* Exit program. */
return 0;
}
/* */
/* This function evaluates the sinc function. */
double sinc(double x)
{
if (fabs(x) < 0.0001)
return 1.0;
else
return sin(PI*x)/(PI*x);

}

//Recursive factorial
//This function calculates the factorial for a user-given integer
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(void)
{
  int n;
  //Declare function prototype
  double factorial_r(int k);
  //Ask for user to input integer
  printf("Enter positive integer: \n");
  scanf("%i",&n);
  //Print values
  printf("Recursive: %i!= %d \n",n,factorial_r(n));
  return 0;
}

//Recursive factorial function
double factorial_r(double k)
{
  //Function will continue until k reaches 0
  if(k==0)
  {
    return 1;
  }
  else
  {
    return k*factorial_r(k-1);
  }

}

Homework

Lab

This program utilized a pir sensor and a light sensor. The goal was to have an LED light up every time the pir detected motion, and to do certain actions when it did not detect motion, as noted in the comments in my code. 

//Define pins

const int led=9;

const int cds=A0;

const int pir=2;

int count=0;

int val=0;

boolean currentbutton=LOW;

boolean lastbutton=LOW;

int k=0;

void setup() {

  // put your setup code here, to run once:

  pinMode(led,OUTPUT);

  pinMode(cds,INPUT);

  pinMode(pir,INPUT);

  digitalWrite(led,LOW);

  Serial.begin(9600);

}

//Create debounce function

boolean debounce(boolean last)

{

  boolean current=digitalRead(pir);

  if(last!=current)

  {

    delay(5);

    current=digitalRead(pir);

  }

  return current;

}

void loop() {

  // put your main code here, to run repeatedly:

  //Use debounce function to ensure that it does not continuously count, and increments neatly

  currentbutton=debounce(lastbutton);

  //If the pir is high, the light will turn on, and the count increments by one

  if(lastbutton==LOW && currentbutton==HIGH)

  {

    digitalWrite(led,HIGH);

    count++;

    Serial.print("Count: ");

    Serial.println(count);

  }

  lastbutton=currentbutton;

  //If the pir is low, we will do one of two things depending on the reading of the light sensor

  if(currentbutton==LOW)

  {

    val=analogRead(cds);

    //If the light sensor is uncovered, the reading will be over 300 and therefore I write the led low

    if(val>300 && digitalRead(pir)==LOW)

    {

      digitalWrite(led,LOW);

    }

    //If the light sensor is covered, the reading will be 300 or less

    //I therefore want the led to blink the amount of times the pir has been activated

    if(val<=300 && digitalRead(pir)==LOW)

    {

      //By using a while loop, I can have the code to make the LED blink the amount of times I want it to

      while(k<=count)

      {

        digitalWrite(led,HIGH);

        delay(250);

        digitalWrite(led,LOW);

        delay(250);

        k++;

        //Once I reach the count, I reset k to 0 and write the LED low for 1000 milliseconds to indicate a reset

        if(k==count)

        {

          k=0;

          digitalWrite(led,LOW);

          delay(1000);

          break;

        }

      }

    }

  }

}

Programming

//GPS Distances//
//This program calculates the distance between two GPS coordinates//
#include <stdio.h>
#include <math.h>

//Create function to calculate angle between vectors//
double angle(double x1,double y1,double z1,double x2,double y2,double z2)
{
  double adotb=x1*x2+y1*y2+z1*z2;
  double maga=sqrt(x1*x1+y1*y1+z1*z1);
  double magb=sqrt(x2*x2+y2*y2+z2*z2);
  double angle=acos(adotb/(maga*magb));
  return angle;
}

//Function to calculate distance between two vectors//

float gc_distance(float firstlat, float firstlong, float secondlat, float secondlong){

//Define values//
  float pi=3.14159265;
  float x1, y1, z1, x2, y2 ,z2;
  float phi1,theta1,phi2,theta2;
  float rho=3960;

  //Find angles//
  phi1=(90-firstlat)*pi/180;
  theta1=(360-firstlong)*pi/180;
  phi2=(90-secondlat)*pi/180;
  theta2=(360-secondlong)*pi/180;

  //Find rectangular coordinates//
  x1=rho*sin(phi1)*cos(theta1);
  y1=rho*sin(phi1)*sin(theta1);
  z1=rho*cos(phi1);
  x2=rho*sin(phi2)*cos(theta2);
  y2=rho*sin(phi2)*sin(theta2);
  z2=rho*cos(phi2);

  //Use angle function to find angle between rectangular coordinates//
  //Multiply by radius to find distance//
double ans=3960*angle(x1,y1,z1,x2,y2,z2);
  //Print result
  return ans;
  }
int main(void){
  int lat_val1, long_val1,lat_val2,long_val2;
  float firstlat, firstlong, secondlat, secondlong;

  //Read latitude and longitude for first point//
  printf("Input the latitude and longitude of the first city\n");
  scanf("%f %f",&firstlat,&firstlong);

  //Find out if latitude is north or south and adjust accordingly//
  printf("Is the value of latitude north or south? Enter 1 for north   and 2 for south.\n");
  scanf("%i",&lat_val1);
  if(lat_val1==2)
  {
    firstlat=-firstlat;
  }

  //Find out if longitude is east or west//
  printf("Is the value of longitude east or west? Enter 1 for west   and 2 for east\n");
  scanf("%i",&long_val1);
  if(long_val1==2)
  {
    firstlong=-firstlong;
  }


  //Read latitude and longitude for second point//
  printf("Input the latitude and longitude of the second city\n");
  scanf("%f %f",&secondlat,&secondlong);

  //Find out whether latitude value is north or south and adjust   accordingly//
  printf("Is the value of latitude north or south? Enter 1 for north   and 2 for south.\n");
  scanf("%i",&lat_val2);
  if(lat_val2==2)
  {
     secondlat=-secondlat;
  }

  //Find out whether longitude is east or west//
  printf("Is the value of longitude east or west? Enter 1 for west  and 2 for east\n");
  scanf("%i",&long_val2);
  if(long_val1==2)
  {
    secondlong=-secondlong;
  }

  //Use function to calculate distance//
  float  distance=gc_distance(firstlat,firstlong,secondlat,secondlong);
  printf("Distance: %4.3f miles\n",distance);
  return 0;
}