Home of Industrial design student Ganesh Ram

Here, the goal is to use the I/O pins of arduino to control the action of LEDs in the form of a 3x3 matrix. Adding buttons to it and doing specific actions with the press of buttons(glowing all LEDs 5 times and to spell out some pre-specified pattern). With normal methods, 10 pins are required for controlling the LEDs(with common ground) and couple of extra GPIO pins for the push button/switches. If that number seems extra for making a bunch of LEDs glow, you're right. In forward bias, LEDs convert electrical energy into light and in reverse bias, generally don't flow of electricity due to high resistance(more on this here. So this means we can technically use the same two I/O pins to make two LEDs glow, albeit not at the same time(or can we?). This property of microcontroller port is called as tri-state logic, where the I/O pin can assume either a positive high value, a zero value or simply switched off/disconnected. This method with multiple pins, is called Charlieplexing, where n pins can be used to drive n(n-1) LEDs(or 2*nC2 for you math nerds). With 3 pins, we can drive 6 LEDs or with 4 pins 12 LEDs. We used 4 pins to drive 9 LEDs here. That's still more than a 100% saving on I/O pins compared to directly driving the LEDs. Then we have the additional matter of driving multiple LEDs at the same time for which we will use a form of visual trickery called Persistence of Vision. This basically means that if we switch the LED cycling fast enough, then all LEDs will seem to glow at the same time.

In the GIFs above, the delay is varied from 1000ms to 2ms. 2ms equals to 500Hz frequency in changing LEDs and looks like continuous glow, and for all practical purposes, it can be assumed to be since we see it that way. You can see the banding by switching on video stabilization in your camera or changing the refresh rate to 50Hz

The circuit diagram for this exercise along with charlieplexing is below.

and the code for this can be found here. Serial input along with functions for button press is also included in the code as in the attached code snippet below.


      	  	 if (Serial.available()) {
    input = Serial.read();//read the input
    if (input == 'a' || input == 'A') 
    {
      for(i=0;i<=50;i++)
       {
          A();
       }
    }

    if (input == 'b' || input == 'B') 
    {
      for(i=0;i<=50;i++)
       {
          B();
       }
    }


	void set_pins(int high_pin, int low_pin)
{
   reset_pins();
   pinMode(high_pin, OUTPUT);
   pinMode(low_pin, OUTPUT);
   digitalWrite(high_pin, HIGH);
   digitalWrite(low_pin,LOW);
}

void reset_pins()
{
   pinMode(LED_1, INPUT); 
   pinMode(LED_2, INPUT);
   pinMode(LED_3, INPUT);
   pinMode(LED_4, INPUT);
   digitalWrite(LED_1, LOW);
   digitalWrite(LED_2, LOW);
   digitalWrite(LED_3, LOW);
   digitalWrite(LED_4, LOW);
}

void A()
{

   

   set_pins(LED_1, LED_2); //LED 1A
   delay(2);                
   set_pins(LED_2, LED_1); //LED 1B
   delay(2);
   set_pins(LED_1, LED_4);  //LED 1C
   delay(2);
   set_pins(LED_4, LED_1); //LED 2C
   delay(2);
 //  set_pins(LED_3, LED_2); //LED 2B
   delay(2); 
   set_pins(LED_2, LED_3); //LED 2A
   delay(2); 
   set_pins(LED_2, LED_4); //LED 3C
   delay(2);
  // set_pins(LED_3, LED_4); //LED 3B
   delay(2); 
   set_pins(LED_4, LED_3); //LED 3A
   delay(2); 
   
 
}

When the first button is pressed, the LEDs are programmed to spell "IITD". This can be changed to anything by including the defined function for all letters(numbers are not yet included in the code and can also be added easily).

When the second button is pressed, the all LEDs blink 5 times.

and finally, accepting serial input from the PC and displaying the characters on the LEDs which in this case are the names involved in this exercise, Anand and Ganesh.

Here we use a speaker/beeper as an output device from the arduino and can use it to create sound in various frequencies. First we'd be using just the speaker as an output from the arduino and re-create some MIDI music. Reacreate some old video games music from the age of Windows 95 and 98.

For this we use the Playtunes library which is available for download from GitHub. We also use tone converter which can convert MIDI music format to one which is recognized by arduino using the playtunes library. MidiTones is one such software which runs on the commandline and can be used to convert .mid file types to .c file types which can be pasted in the arduino code to play the file on a piezo buzzer.

Use the following code and copy paste the c file generated by MidiTones



#include Playtune.h
 

//copy paste content of converted midi file here.ie: (yourtone).c

 

Playtune pt;

void setup() {
pt.tune_initchan (10);
pt.tune_initchan (11);
pt.tune_initchan (12);
}

void loop () {
pt.tune_playscore (score); /* start playing */
while (pt.tune_playing) ; /* wait here until playing stops */
}

The circuit was built on arduino and tested with the generated code

Code and Circuit can be found in the TinkerCad link below.

For both input and output device in use, Please check the theremin project tab

Steps in this assignment - Connecting a bluetooth module to arduino, Connecting the LED Matrix MAX 7219 to the arduino, Making the app using MIT App inventor and Making the connections and uploading the code for the same.

The bluetooth module is connected to the arduino as shown below

For testing out the module, the following code can be used by connecting an LED between pin 7 and GND



#define ledPin 7
    int state = 0;
    void setup() {
      pinMode(ledPin, OUTPUT);
      digitalWrite(ledPin, LOW);
      Serial.begin(38400); // Default communication rate of the Bluetooth module
    }
    void loop() {
      if(Serial.available() > 0){ // Checks whether data is comming from the serial port
        state = Serial.read(); // Reads the data from the serial port
     }
     if (state == '0') {
      digitalWrite(ledPin, LOW); // Turn LED OFF
      Serial.println("LED: OFF"); // Send back, to the phone, the String "LED: ON"
      state = 0;
     }
     else if (state == '1') {
      digitalWrite(ledPin, HIGH);
      Serial.println("LED: ON");;
      state = 0;
     } 
    }

Next, the MAX 7219 can be connected to Arduino as shown below and tested for functionality using the LEDControl.h header file. The MAX7219 LED matrix has 8x8 LEDs or 64 individual LEDs which can be controlled.

Using the MIT App inventor

The MIT app inventor was used here to build the android app for LED control and displaying the text on the LED matrix. We start here by defining the layout of the app and building further on that

The .APK file for the app that was build can be found here.

The connections are made on the breadboard as shown below

Power Tool Design

Two Wheeler Helmet Safety Improvement

Course Project Ideation

Website Development for Course

Programming assignment files

C Programs

Python Codes

Arduino LED Matrix Assignment(using Charlieplexing)

Input Devices and Experiment

Sensors in Android Phone

Output Devices and Experiment

Displaying text on a LED Matrix through Bluetooth module using app

Using the MIT App inventor

Project Proposal for DSL810

Digital Music Mini Orchestra (Theremin, Chaldni Plate and Musical Floppy drive)

Ganesh Ram

Prototype and Testing