delta modulation

Hi to everyone, i want to convert an analog signal to digital with Arduino board, using delta modulation and then to graph the results with processing language.
Delta modulation (DM or ?-modulation) is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance. DM is the simplest form of differential pulse-code modulation (DPCM) where the difference between successive samples is encoded into n-bit data streams. In delta modulation, the transmitted data is reduced to a 1-bit data stream.
Its main features are:
the analog signal is approximated with a series of segments
each segment of the approximated signal is compared to the original analog wave to determine the increase or decrease in relative amplitude
the decision process for establishing the state of successive bits is determined by this comparison
only the change of information is sent, that is, only an increase or decrease of the signal amplitude from the previous sample is sent whereas a no-change condition causes the modulated signal to remain at the same 0 or 1 state of the previous sample.

Here is the code i have now but i want help
Arduino code

int currReading;
int prevReading = 0;
void setup()
// initialize the serial communication:
// this code is for analog-to-digital on arduino
void loop()
// send the value of analog input 0:
currReading = analogRead(0);
int delta = currReading - prevReading;

prevReading = currReading;
// wait a bit for the analog-to-digital converter
// to stabilize after the last reading:

/* Processing code for this example

// Graphing sketch

// This program takes ASCII-encoded strings
// from the serial port at 9600 baud and graphs them. It expects values in the
// range 0 to 1023, followed by a newline, or newline and carriage return

// Created 20 Apr 2005
// Updated 18 Jan 2008
// by Tom Igoe
// This example code is in the public domain.

import processing.serial.*;

Serial myPort; // The serial port
int xPos = 1; // horizontal position of the graph

void setup () {
// set the window size:
size(400, 300);

// List all the available serial ports
// I know that the first port in the serial list on my mac
// is always my Arduino, so I open Serial.list()[0].
// Open whatever port is the one you're using.
myPort = new Serial(this, Serial.list()[0], 9600);
// don't generate a serialEvent() unless you get a newline character:
// set inital background:
void draw () {
// everything happens in the serialEvent()

void serialEvent (Serial myPort) {
// get the ASCII string:
String inString = myPort.readStringUntil('\n');

if (inString != null) {
// trim off any whitespace:
inString = trim(inString);
// convert to an int and map to the screen height:
float inByte = float(inString);
inByte = map(inByte, 0, 1023, 0, height);

// draw the line:
line(xPos, height, xPos, height - inByte);

// at the edge of the screen, go back to the beginning:
if (xPos >= width) {
xPos = 0;
else {
// increment the horizontal position: