Nice work
I just wrapped your code up in the forum friendly code displayer (the little # button above when you post)
Just so its easier to read.
Top job 
/*
* Morse Code Decoder and door opener
*
* Josh Myer <josh@joshisanerd.com>
*
* 20090103 rev 0 -- ugly and unfortunate, but mostly functional (my first arduino code)
*
* Hook a debounced switch up to digital pin 2, like you would for the Button demo.
*
* This code reads morse code from digital02, turning it into ASCII characters.
* If you key in "SOS" (... --- ...), it will turn on the LED on digital13.
*
* The intended application is to let me key in a password at my apartment's
* front gate and have it automatically let me into the building, instead of
* fumbling around for keys.
*
* There's still lots of stuff to do and clean up, but I wanted to share the idea
* and the current implementation to help spur people on.
*/
#include <avr/pgmspace.h>
#include <string.h>
int ledPin = 13; // choose the pin for the LED
int inputPin = 2; // choose the input pin (for a pushbutton)
int val = 0; // variable for reading the pin status
#define THRESHOLD 3
#define DELAY_TIME 10 // ms
int n_since_zero = 0;
int n_in_zero = 0;
#define NCHARS 26+10+3
char morse_chars[NCHARS] = {
'A',
'B',
'C',
'D',
'E',
'F',
'G',
'H',
'I',
'J',
'K',
'L',
'M',
'N',
'O',
'P',
'Q',
'R',
'S',
'T',
'U',
'V',
'W',
'X',
'Y',
'Z',
'0',
'1',
'2',
'3',
'4',
'5',
'6',
'7',
'8',
'9',
'.',
',',
'?',
};
char* morse_strings[NCHARS] = {
".-",
"-...",
"-.-.",
"-..",
".",
"..-.",
"--.",
"....",
"..",
".---",
"-.-",
".-..",
"--",
"-.",
"---",
".--.",
"--.-",
".-.",
"...",
"-",
"..-",
"...-",
".--",
"-..-",
"-.--",
"--..",
"-----",
".----",
"..---",
"...--",
"....-",
".....",
"-....",
"--...",
"---..",
"----.",
".-.-.-",
"--..--",
"..--..",
};
#define PAUSE 0
#define DIT 1
#define DAH 2
#define DDLEN 5
char passwd[] = "SOS";
char chars_rx[10];
int char_cursor= 0;
int ditsdahs[DDLEN];
int dd_cursor = 0;
void setup() {
pinMode(ledPin, OUTPUT); // declare LED as output
pinMode(inputPin, INPUT); // declare pushbutton as input
for (int i = 0; i < DDLEN; i++) {
ditsdahs[i] = 0;
}
dd_cursor = 0;
for (int i = 0; i < 10; i++) {
chars_rx[i] = 0;
}
char_cursor = 0;
Serial.begin(9600);
}
void dd_print() {
Serial.print(" > DD BUF: ");
for(int i = 0; i < DDLEN; i++) {
Serial.print(ditsdahs[i]);
Serial.print(", ");
}
Serial.println();
}
boolean dd_eq(char*buf) {
if(ditsdahs[0] == PAUSE) return false;
int i;
for(i = 0; ditsdahs[i] != PAUSE && i < DDLEN; i++) {
if (ditsdahs[i] == DIT && buf[i] == '-') {
return false;
}
if (ditsdahs[i] == DAH && buf[i] == '.') {
return false;
}
}
/*
Serial.print("Got to the end of ");
Serial.print(buf);
Serial.print("; checking strlen=");
Serial.print(strlen(buf));
Serial.print(" == i=");
Serial.println(i);
*/
if (i != strlen(buf)) return false;
return true;
}
void dd_decode() {
for(int i = 0; i < NCHARS; i++) {
/*
Serial.print("dd_decode: check i=");
Serial.print(i);
Serial.print(" , string=\"");
Serial.print(morse_strings[i]);
Serial.print("\", c=");
Serial.print(morse_chars[i]);
Serial.println();
*/
if (dd_eq(morse_strings[i])) {
char c = morse_chars[i];
char_emit(c);
break;
}
}
for (int i = 0; i < DDLEN; i++) {
ditsdahs[i] = 0;
}
dd_cursor = 0;
}
void check_passwd() {
Serial.print("Check password: ");
Serial.print(chars_rx);
Serial.println();
if (0 != strstr(chars_rx, passwd)) {
digitalWrite(ledPin, HIGH);
}
/*
for (int i = 0; i < 10; i++) {
chars_rx[i] = 0;
}
char_cursor = 0;
*/
}
void char_emit(char c) {
Serial.print("Got a char: c=");
Serial.println(c);
chars_rx[char_cursor] = c;
char_cursor++;
if (char_cursor >= strlen(passwd)) {
check_passwd();
}
}
void dd_emit(int v) {
ditsdahs[dd_cursor] = v;
dd_cursor++;
dd_print();
if (v == PAUSE)
dd_decode();
}
void dit() {
dd_emit(DIT);
Serial.println("DIT");
}
void dah() {
dd_emit(DAH);
Serial.println("DAH");
}
void pause() {
dd_emit(PAUSE);
Serial.println("PAUSE");
}
void loop(){
val = digitalRead(inputPin); // read input value
if (val == LOW) {
if (n_since_zero > 5) {
/* Serial.print("CROSS LOW AFTER ");
Serial.println(n_since_zero);
*/
if (n_since_zero > 16) {
dah();
}
else {
dit();
}
}
n_since_zero = 0;
n_in_zero++;
}
else {
n_since_zero++;
}
if (n_in_zero == 20) {
pause();
}
if (n_since_zero > THRESHOLD) {
if (n_in_zero > 0) {
// Serial.print("CROSS HIGH AFTER ");
//Serial.print(" > ");
// Serial.println(n_in_zero);
// Serial.println("**************************");
}
n_in_zero = 0;
// digitalWrite(ledPin, HIGH);
}
else {
// digitalWrite(ledPin, LOW);
}
delay(DELAY_TIME);
}