Gesture control for PowerPoint presentation

Basic idea of the project

The intention of this tutorial is to learn how to control computer keyboard and mouse events using your micro-controller. For demonstration I have chosen to name the project as gesture control for PowerPoint presentation. At the end of this tutorial you will be able to control the slides using your gestures. Now in order to control the operating system you need a language like python, java, c++ etc. I find python affable and powerful so I’ll be using that for coding. You can use any language you want but the logic and algorithm will remain the same, only the syntax will differ. I won’t be teaching you python in this post that is beyond the scope of this post. If you want to learn the language there is plethora of content available online. You just need a net connection and off you go.
P.S. : If you like the posts do like and share them with others.

Python

Python is an easy to learn high level programming language. It is a beautiful and a very powerful language. The packages that are available make it kind of limitless. Some of the places where python is used are mentioned below.

  • Google makes extensive use of Python in its web search systems.
  • The popular YouTube video sharing service is largely written in Python.
  • The Dropbox storage service codes both its server and desktop client software primarily in Python.
  • The Raspberry Pi single-board computer promotes Python as its educational language.
  • NASA, Los Alamos, Fermilab, JPL, and others use Python for scientific programming tasks.

So we know that most of the big shots use python. Now they use it for a reason and the reason being that its simply an awesome language. If you want to start learning programming you ought to start with python. Here are a list of sites and books that you may use for learning python.

  1. https://www.python.org/about/gettingstarted/ (This is the official page where you can learn how to install the IDE and get started.)
  2. Learning Python, 5th Edition (This is a good book if you are new to programming and otherwise as well.)
  3. http://www.learnpython.org/
  4. http://www.tutorialspoint.com/python/

Once you get the hang of it then you can directly use the documentations for learning how to use the packages.

pySerial and PyUserInput

We will be requiring these modules in our project. The names are quite self explanatory the former is for serial communication while the latter is for the mouse and keyboard events. The links to these modules are:

Well download these and install them. I recommend you to use 32bit python 2.7 version modules as well as the language. Because most of the modules are available for 2.7 version.

Components and Software requirements

  • A microcontroller board with UART capability e.g. MSP430G2 Launchpad, Arduino Uno board etc.
  • An accelerometer e.g. ADXL335 etc..
  • Python 2.7 , pySerial & PyUserInput modules

Connections

connections

I have used fritzing for making this. Here is the link to their home page.  http://fritzing.org/home/

Logic

We will calibrate the accelerometer and take readings for left and right position. Use the serial monitor for this. Read my tutorial titled Capacitive Accelerometer Interfacing if you don’t know what I am talking about. Next once you have those digital values you need to make the program for slide control. We know that left arrow and right arrow keys are used for navigation purpose. So in our python script the if statements will contain code for left arrow button press and right arrow button press. Note that you are reading the values that the controller is sending serially using python and taking decisions based on that value.

Energia Code

int x_pin = A0;
void setup()
{
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(x_pin,INPUT);
  analogReference(INTERNAL2V5);
}

void loop()
{
  // put your main code here, to run repeatedly:
  int x = analogRead(x_pin);
  Serial.println(x);
  delay(500);
}

Python Script

__author__ = 'MANPREET'
'''
This is a file for controlling keyboard events.
'''
from pykeyboard import PyKeyboard
import serial
import time

comPort = raw_input("Please enter the COM port number")
baudRate = raw_input("Please enter the baud rate")
myserial = serial.Serial(comPort, baudRate)
k = PyKeyboard()
TRUE = 1;
try:
    while (TRUE):
        if (myserial.inWaiting()):
            mydata = myserial.readline()
            x = int(mydata)
            print(x)
            if x > 650:
                k.tap_key(k.left_key)
                print("left")
                time.sleep(1)
            if x < 550:
                k.tap_key(k.right_key)
                print("right")
                time.sleep(1)
except KeyboardInterrupt:
    print("stop")

Code Explanation

The Energia code is pretty straightforward but still just to cover that as well. We have declared A0 i.e. P1.0 pin as input and changed the ADC reference voltage to 2.5V in line 7. Next part is just getting the ADC reading and sending it serially.

The python code demands some explanation. So lets begin understanding the code .

from pykeyboard import PyKeyboard
import serial
import time

This code will import three modules PyKeyboard, serial and time. For the pykeyboard we have imported the constructor. Then you have made one object k using the same.

comPort = raw_input("Please enter the COM port number")
baudRate = raw_input("Please enter the baud rate")
myserial = serial.Serial(comPort, baudRate)
k = PyKeyboard()

myserial is an object of the serial module that you have imported. You will use this to access its functions. The raw_input() is for taking the com port and baud rate values from the user. Example COM11 and 9600.

TRUE = 1;
try:
    while (TRUE):
        if (myserial.inWaiting()):
            mydata = myserial.readline()
            x = int(mydata)
            print(x)
            if x > 650:
                k.tap_key(k.left_key)
                print("left")
                time.sleep(1)
            if x < 550:
                k.tap_key(k.right_key)
                print("right")
                time.sleep(1)
except KeyboardInterrupt:
    print("stop")

Well this is an infinite loop and you are checking this block for keyboard interrupt i.e. ctrl+c . This is done so that you can come out of the program properly without having to kill the program. Next we are checking if there is data in the serial buffer. If yes then we are storing it in mydata variable. Convert it into integer and store it as some variable say x. Next step is easy write two if statements and include the code and condition for left arrow button press and right arrow button press. For more details of the PyKeyboard module visit : https://pypi.python.org/pypi/PyUserInput/0.1.9
For running the python script install python 2.7. Copy paste the python script code into notepad and save it as gersturecontrol.py(or any name for that matter) Then follow these steps.

  1. Open command prompt(Press windows+r, then type cmd and press enter.)
  2. opening_command_prompt

  3. Change the directory to the one containing your python script i.e. the .py file. Use cd for that.
  4. file_location

  5. Use python gesturecontrol.py for running your code
  6. running the program

  7. For stopping the code press ctrl+c

Thank you for reading the post and hope that it was helpful.If you like the post do share it with others and spread the knowledge.

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Serial Communication

Hello!! Before I start this post I want to say that if anyone of you wants to add me to their linkedin network here is my profile link : in.linkedin.com/in/msminhas93/

Often we need to communicate between two devices. This can be either parallel or serial. In parallel communication there is an individual data line for each bit, so normally there would be 8 data lines for 8 bit data. In asynchronous we require only two lines. One for transmission and the other for reception.

Theory

So the main thing in serial communication is ‘baud rate’. It is nothing but the bits sent per second. In serial asynchronous communication the baud rate of both transmitter and receiver have to be equal. If there is any mismatch there is bound to be error in sending and receiving data.

Now you might wonder what is sent serially? The answer is ASCII values of the character or symbol to be transmitted is sent serially. Now ASCII is a 7 bit hex code. There is the extended ASCII code as well. You can find all the ASCII values here.

Now let us take an example. Suppose I want to send character M serially. The ASCII value of M is 0x4D. The binary equivalent is 0b01001101. Now we send this data as pulses, changing the bits after the time 1/baud_rate.

070120141331

So this is how the serial data looks like. Some of you might have this doubt that how on earth will the processor or controller come to know that the other party is transmitting data and it has to take those bits. This is a very good doubt.

The beginning of serial data is marked by a start bit and on similar grounds there is a stop bit or two. Just like one normally says ‘hello’ at the start of a conversation and ‘bye’ at the end we send the start and stop bits for the same purpose.

The other question that may arise in the mind of the curious is that what if there is noise in the system? This is a valid question as well. So there are error checking bits like parity bits which are sent along with the data serially. (Parity can be even or odd. Now if the system uses even parity, then it will make the number of ‘1’ bits in the data even by adding 1 or 0. So if the data already has even number of ones the even parity bit is 0 and if the data has odd number of ones then the even parity bit is set or is 1 so that the total number of ones in the data is even.) Well this sums up asynchronous serial communication part.

Now this is known as UART module in the microcontrollers. UART stands for universal asynchronous transmitter and receiver. Most modern microcontrollers have a dedicated hardware for asynchronous serial communication called UART. msp430 also has this facility. Now what this means that you have to just configure the peripheral and the baud rate generation, parity bits and all other factors as well as the receiving part is done by this hardware. (If you wanted to send data serially without hardware dedicated for the same you would have to make the port high and low, use delay subroutines and the rotate instructions for doing the same task. The detection will also be tedious.)

This is how the data will look when  you send it via UART module.

w_example

Well let’s begin with the USCI module that provided in the msp430 micro controllers. This provides a UART mode for asynchronous serial communication. There are few basic initialization registers like all peripherals of msp430. Note that you can use grace for initializing the UART mode. But I’ll be covering the normal method by using the command registers and configuring it to meet our needs.

Let us begin.

UART mode features include:
• 7- or 8-bit data with odd, even, or non-parity
• Independent transmit and receive shift registers
• Separate transmit and receive buffer registers
• LSB-first or MSB-first data transmit and receive
• Built-in idle-line and address-bit communication protocols for multiprocessor systems
• Receiver start-edge detection for auto-wake up from LPMx modes
• Programmable baud rate with modulation for fractional baud rate support
• Status flags for error detection and suppression
• Status flags for address detection
• Independent interrupt capability for receive and transmit

The list of all registers related to the UART mode are listed below.

registers_list

Now the procedure how to initialize these registers is given in the msp430g2 user manual.

initializing

Just set those bits which you want as per the explanation given in the user guide.

Then there are the UCA0TXBUF and UCA0RXBUF via which the serial data is transmitted and received respectively. If you want to send any character just put it in the UCA0TXBUF register and it will be transmitted. Just check whether the byte has been sent or not by checking the UCA0TXIFG bit of IFG2 register. If it is set means the module is busy sending the previous byte or data and one has to wait till it is reset.

With this background you should be able to program the controller to send and receive data.

Before we shift to the program there is something that I need to tell you. For hardware UART via launchpad without having to use the rs232 cable and max232 IC. For newer launchpad versions i.e. 1.5 and above there is the position of the jumpers printed on the launchpad itself for hardware UART and software UART respectively.

Hardware UART on Launchpad 1.4

If you have a Launchpad of v1.4 (versions that have no ‘Rev x.x’ printed below the ‘MSP-EXP430G2’ label are pre 1.5) is is possible to use hardware UART by replacing the MSP430 with a newer model, such as the MSP430G2553 and then cross connecting the serial pins in header J3 i.e the TXD and RXD(use a cross jumper or female to female wires for the same.)

Program

#include "serial.h"
#include "lcd.h"
int main(void) {
    WDTCTL = WDTPW | WDTHOLD;	// Stop watchdog timer
    uart_init();
    lcd_init();
    IE2 |= UCA0RXIE;
    println("START");
    __bis_SR_register(LPM0_bits + GIE);
}
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR(void)
{
	if(UCA0RXBUF == '0')
        {
            send_command(0x01);
        }
	else
        send_data(UCA0RXBUF);
}

/*
 *  serial.h
 *  Created on   	: 01-Jan-2014 12:25:06 PM
 *  Author	  	: Manpreet Singh Minhas
 *  Website		: https://learningmsp430.wordpress.com/
 *  This is a standard header for 9600 baud rate serial communication.
 */

#ifndef SERIAL_H_
#define SERIAL_H_

#include<msp430g2553.h>// Change this as per your micro-controller chip.
void uart_init(void);
void send_byte(int data);
void print(char *data);
void println(char *data);
void send_int(int a);
void send_intln(int a);
void uart_init()
{
	P1SEL  |= BIT1|BIT2; // Port for UART transmission and reception purpose.
	P1SEL2 |= BIT1|BIT2;
    UCA0CTL1 |= UCSWRST; // Software reset
    UCA0CTL1 |= UCSSEL_1;// Select ACLK
    UCA0BR0 = 3;// This is the count for getting 9600 baud rate 32768/9600 = 3.4133
    UCA0BR1 = 0;
    UCA0MCTL = UCBRS1 + UCBRS0;// Modulation bits = 0b00000011
    UCA0CTL1 &= ~UCSWRST;	// Start the UART
}
void send_byte(int data)
{
	while (!(IFG2&UCA0TXIFG));
	UCA0TXBUF = data;
}
void print(char *data)
{
	while(*data)
	{
		send_byte(*data);
		data++;
	}
}
void println(char *data)
{
	while(*data)
	{
		send_byte(*data);
		data++;
	}
	send_byte('\n');
	send_byte('\r');
}
void send_int(int a)
{
	int temp;
	int rev=0;
	int dummy =a;
	 while (dummy)
	   {
	      rev = rev * 10;
	      rev = rev + dummy%10;
	      dummy = dummy/10;
	   }
	while(rev)
	{
		temp=rev%10;
		send_byte(0x30+temp);
		rev /=10;
	}
}
void send_intln(int a)
{
	int temp;
	int rev=0;
	int dummy =a;
	 while (dummy)
	   {
	      rev = rev * 10;
	      rev = rev + dummy%10;
	      dummy = dummy/10;
	   }
	while(rev)
	{
		temp=rev%10;
		send_byte(0x30+temp);
		rev /=10;
	}
	 send_byte('\n');
	 send_byte('\r');
}
#endif/* SERIAL_H_ */

Well this program will send the data received serially to lcd. For sending data you will require a software like hyper terminal, putty, energia serial monitor, arduino serial monitor etc. So just configure that to 9600 baud rate with no parity bits and only one stop bit and you are all set to send data serially. If you have any problem you can comment or send me mail.

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