Hello guys
So I have a project to display time and temperature data logger, which also could sent SMS when there was any temperature rise
Instead of using a RTC module, I used RTC attached to SIM 900. My problem is:
- How to take date/time data from AT+CCLK command and print the timestamp to the LCD screen (yeah i used LCD screen as a display monitor for user)?
Here is my experiment code, which inspired from this post Data processing. Getting time and date. - Syntax & Programs - Arduino Forum
#include <LiquidCrystal.h>
#include "SIM900.h"
#include <SoftwareSerial.h>
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
SoftwareSerial mySerial(2, 3); // RX, TX
int i=0;
#define CCLK_MSG_LEN 28 // total characters in the CCLK message
#define TIME_STR_LEN 18 // the actual number of characters for date and time
char timeStr[TIME_STR_LEN]; // holds the time string
char timePreamble[] = "CCLK: \"" ; // there is a quotation mark in the string so we need the C escape char
void setup(){
lcd.begin(16, 2);
Serial.begin(9600);
Serial.println("GSM Shield testing.");
gsm.begin(9600);
//Start configuration of shield with baudrate.
//For http uses is raccomanded to use 4800 or slower.
mySerial.begin(9600);
mySerial.println( "AT+CLTS=1");
mySerial.println( "AT+CCLK =\"15/06/23,13:28:00+28\"");
lcd.setCursor(0,0);
lcd.print("Just Testing");
mySerial.println( "AT+CCLK?" );
}
boolean getTime(){
if(mySerial.available() >= CCLK_MSG_LEN ){
if(mySerial.read() == '+'){ // check if start of string
for(int i=0; i < strlen(timePreamble); i++){
if(mySerial.read() != timePreamble[i] )
return false; // exit if the received data does not match the preamble
}
// we are now at the start of the time data
for(int i=i; i < TIME_STR_LEN; i++)
timeStr[i] = mySerial.read();
return true; // we have filled the timeString with valid data
}
}
return false; // we dont have a full message starting with the CCLK preamble
}
// converts two characters from date string into a two digit decimal value
int dateToDecimal(char * date){
int value = ((date[0] - '0') * 10) + (date[1] - '0');
return value;
}
void loop()
{
int a, b, c, d, e, f;
if(getTime() == true){
a = dateToDecimal(&timeStr[0]) ;
b = dateToDecimal(&timeStr[3]) ;
c = dateToDecimal(&timeStr[6]) ;
d = dateToDecimal(&timeStr[9]) ;
e = dateToDecimal(&timeStr[12]) ;
f = dateToDecimal(&timeStr[15]) ;}
lcd.setCursor(0,1);
lcd.print(c);
lcd.print("/");
lcd.print(b);
lcd.print("/");
lcd.print(a);
lcd.print(" ");
lcd.print(d);
lcd.print(":");
lcd.print(e); //this line of code use to create dd:mm:yy hh:mm
delay(10000);}
but the current result from this code, my LCD screen shows unknown numbers 4357/257/0 659:4546
any idea why this thing happened? Thank you so much and sorry for my bad english 
I think your problem is here:
for(int i=i; i < TIME_STR_LEN; i++)
Shouldn't 'i' start at zero?
johnwasser:
I think your problem is here:
for(int i=i; i < TIME_STR_LEN; i++)
Shouldn't 'i' start at zero?
thank you johnwasser, i already changed i=0 but the it still shows unknown sequence of numbers
i did some modification in code, to check where the error happens. I put 'else' condition after if statement
if(getTime() == true){
a = dateToDecimal(&timeStr[0]) ;
b = dateToDecimal(&timeStr[3]) ;
c = dateToDecimal(&timeStr[6]) ;
d = dateToDecimal(&timeStr[9]) ;
e = dateToDecimal(&timeStr[12]) ;
f = dateToDecimal(&timeStr[15]) ;}
else Serial.println("There is something wrong");
and yes, "There is something wrong" is printed on Serial monitor. It seems like getTime() method return false value. And maybe there is something wrong with getTime() method
boolean getTime(){
if(mySerial.available() >= CCLK_MSG_LEN ){
if(mySerial.read() == '+'){ // check if start of string
for(int i=0; i < strlen(timePreamble); i++){
if(mySerial.read() != timePreamble[i] )
return false; // exit if the received data does not match the preamble
}
// we are now at the start of the time data
for(int i=0; i < TIME_STR_LEN; i++)
timeStr[i] = mySerial.read();
return true; // we have filled the timeString with valid data
}
}
return false; // we dont have a full message starting with the CCLK preamble
}
any idea? 
getTime() will return false until at least 27 characters have arrived. It will also return false if the first character read is a '+' and the next seven characters don't match the preamble.
IF THE FIRST CHARACTER IS NOT A '+' it treats the next TIME_STR_LEN characters as a valid time string. There is a very good chance you are hitting a non-'+' character and reading the wrong part of the string.
Try this:
boolean getTime(){
// Check for available bytes
if(mySerial.available() < CCLK_MSG_LEN )
return false; // Not enough characters for a full message. Try again later
if(mySerial.read() != '+')
return false; // Not in sync yet
// In sync. Check the preamble
for(int i=0; i < strlen(timePreamble); i++) {
if(mySerial.read() != timePreamble[i] )
return false; // exit if the received data does not match the preamble
}
// Preamble checked. We are now at the start of the time data
for(int i=0; i < TIME_STR_LEN; i++)
timeStr[i] = mySerial.read();
return true; // we have filled the timeString with valid data
}
johnwasser thank you very much i already use the code, and finally get the right result for each value.
but there is still something weird about it. It only get right in a few second. Later on it shows unknown value (again)
I tried to print the result in serial, here is the result:
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
date components are
15
6
25
10
18
22
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
date components are
15
6
25
-385
-385
-385
date components are
15
6
25
10
19
15
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
There is something wrong
date components are
0
926
404
4357
669
3932
maybe there is something wrong about my baud rate or loop? since the right result only shown in few times