Author: yihanz@andrew.cmu.edu

For this assignment, I used two potentiometers to simulate the “Etch A Sketch” (Wikipedia_”Etch A Sketch”). Using two potentiometer, one controls left and right movement, and the other controls the up and down movement, the browser window is going to serve as a canvas for the “Etch A Sketch” board.

• Parts list:
  • Potentiometer (10K)  x2
  • Adafruit M0 Metro Express
  • Bunch of jumper wires

Fritzing Sketch:

Code (Arduino Part):

Code (js part):

Zip -Etch A Sketch

This is ment to be a toy for cats and dogs, where the closer they are to the toy, the brighter the LED is going to be. And when they put their paws on th button (it’s a photoresistor), the LED with stop for however long they leave their paws in place.

Material:

• 1x  IR distance sensor
• 1x  photoresistor
• 1x  3.3v LED
• 1x  10k potentiometer
• 1x  220 resistor
• Adafruit Metro M0 Express

Setup:

Code:

/*

  Jean Zhang





  This is a sketch about a toy for pets (hopefully).

  This is Ver 1.0 which is a easy prototype, a proof of

  concept that the code/board/sensors works properly.



  This code is modified from the class 2 note from

  Prof. J. Eric Townsend.The lisence is as the following:







  The MIT License (MIT)



  Copyright (c) 2014 J. Eric Townsend



  Permission is hereby granted, free of charge, to any person obtaining a copy

  of this software and associated documentation files (the "Software"), to deal

  in the Software without restriction, including without limitation the rights

  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

  copies of the Software, and to permit persons to whom the Software is

  furnished to do so, subject to the following conditions:



  The above copyright notice and this permission notice shall be included in

  all copies or substantial portions of the Software.



  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

  THE SOFTWARE.



  This code is modified from the original code by Jean Zhang.

  Lots of thanks to Robert Zacharias and Professor Garth Zeglin for helping out with debugging and making the code to properly compile.









*/

const int irPin = 0;

const int photoPin = 1;

const int ledPin = 8;



const int sampleSize = 16;



int irIndex = 0;

int irReadings[sampleSize];



int photoIndex = 0;

int photoReadings[sampleSize];



int distVal, photoVal, ledVal;



const int ambientPhoto = 600;

const int tolerance = 200;







void setup() {

  Serial.begin(115200);



  pinMode(irPin, INPUT);

  pinMode(photoPin, INPUT);

  pinMode(ledPin, OUTPUT);





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



}



void loop() {

  //Reading the values from ir and photoResistor

  int photo = analogRead(photoPin);

  photoReadings[photoIndex] = photo;

  photoIndex = (photoIndex + 1) % sampleSize;



  int irDist = analogRead(irPin);

  irReadings[irIndex] = irDist;

  irIndex = (irIndex + 1) % sampleSize;



  //Get readings for irSensors

  int *pirReadings = irReadings;

  distVal = getVal(pirReadings); // feed the pointer of the array (array location)

//  photoVal = getVal(*photoReadings);







  // console

#if 0

  Serial.print("low ");

  Serial.print(low);

  Serial.print(" high ");

  Serial.print(high);

  Serial.print(" mean ");

  Serial.println(mean);

  Serial.print(" median ");

  Serial.println(median);

  delay(500);

  digitalWrite(photoPin, LOW);

  delay(500);

#endif





  int ledVal = map(distVal, 0, 1023, 0, 255);

  //0 (min) is based on the ambient setting



  if (abs(ambientPhoto - photoVal) > tolerance) {

    ledVal = 0;

  }



  analogWrite(ledPin, ledVal);







}



//Modified from class note:

int getVal(int *readings) { //return mean for now

  int median = 0;

  int low = 1024;

  int high = 0;

  int mean = 0;

  for (int i = 0; i < sampleSize; i++) {

    mean += readings[i];

    if (readings[i] < low) { low = readings[i]; } if (readings[i] > high) {

      high = readings[i];

    }

  }

  mean = mean / sampleSize;

  bubbleSort(readings);

  median = readings[sampleSize / 2];



  return mean;

  //return median

}

//In C, a function cannot return an array









// tigoe's sort for an array

// since bubbleSort changes the array locally, the function doesn't

// need to return any value

void bubbleSort(int *readings) {

  int out, in, swapper;

  for (out = 0 ; out < sampleSize; out++) { // outer loop

    for (in = out; in < (sampleSize - 1); in++) { // inner loop if ( readings[in] > readings[in + 1] ) { // out of order?

        // swap them:

        swapper = readings[in];

        readings [in] = readings[in + 1];

        readings [(in + 1)] = swapper;

      }

    }

  }



}

Reflection:

I haven’t been able to get my hardware to work at the moment (just started testing like 10min ago). I spent a lot of time trying to debug the program. I had lots of issue with C++ since I didn’t really learn how to program in C besides reading codes for reference in my Python Projects (so much less work…).

My biggest issue is with the syntax of functions and the “pointer”  in C. I wanted to make the return median/mean part into a function and use bubbleSort multiple times on different sensor values, where instead of changing the global, it takes in an array and sort that array. The problem being when defining function,  it is defining certain type of data/value. And the take-in value need to be defined for their data type . However, when the take in value is an array, the pointer concept comes into play, and I keep getting the error like this

invalid types 'int[int]' for array subscript

After lots of Google-ing and reading comments I start to understand the concept of pointers and modify my code accordingly. (It is actually a really simple solution, kinda like the x.^x – the dot syntax in MATLAB). Instead of using :

void bubbleSort(int readings) { ........

Simply change the expression into:

void bubbleSort(int *readings) { ........ 

Note the different between “int readings” and “int *readings“.  Where *readings is a pointer and readings is not really a valid input.

I also tried to return an array for bubbleSort, which I don’t have to do that (bad habit writing python programs, it does so much for you).  In C, a function cannot return an array, instead, the way to return arraies is to use pointers, which also gave me a lot of problems when compiling.

Lots of thanks to Robert Zacharias and Professor Garth Zeglin for helping with the bug in the code (mainly for the pointer spaghetti) and making the code compile properly.