Implementation of countdown timer using RTCTimedEvent library

I am trying to use this library for a countdown timer using a DS1307 Real Time Clock. Library is available at http://code.google.com/p/ebl-arduino/wiki/RTCTimedEvent

Experiencing difficulty with coming up with a way to know when a new minute occurs. I do not care about the actual minute; just, when it occurs.

My thought is to make a web page, using images of digits to build a count down clock. Library example:

/*
  Web Server
 
 A simple web server that shows the value of the analog input pins.
 using an Arduino Wiznet Ethernet shield. 
 
 Circuit:
 * Ethernet shield attached to pins 10, 11, 12, 13
 * Analog inputs attached to pins A0 through A5 (optional)
 
 created 18 Dec 2009
 by David A. Mellis
 modified 9 Apr 2012
 by Tom Igoe
 
 */
#include <Wire.h>    //  http://arduino.cc/en/Main/Software  included in download
#include <SPI.h>
#include <Ethernet.h>
#include <RTCTimedEvent.h>

int time;
int time2;

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192,168,2,7);

// Initialize the Ethernet server library
// with the IP address and port you want to use 
// (port 80 is default for HTTP):
EthernetServer server(80);

void setup() {
 // Open serial communications and wait for port to open:
  Serial.begin(9600);
   while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }

  // start the Ethernet connection and the server:
  Ethernet.begin(mac, ip);
  server.begin();
  Serial.print("server is at ");
  Serial.println(Ethernet.localIP());
  
  time =60;  //Initial timer value
  
  //initial buffer for 1 timer
  RTCTimedEvent.initialCapacity = sizeof(RTCTimerInformation)*1;

  //event for every minute
  RTCTimedEvent.addTimer(TIMER_ANY, //minute
                         TIMER_ANY, //hour
                         TIMER_ANY, //day fo week
                         TIMER_ANY, //day
                         TIMER_ANY, //month
                         minuteCall);


}
  
void loop(){

  RTCTimedEvent.loop();
   
  // listen for incoming clients
  EthernetClient client = server.available();
  if (client) {
    Serial.println("new client");
    // an http request ends with a blank line
    boolean currentLineIsBlank = true;
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();
        Serial.write(c);
        // if you've gotten to the end of the line (received a newline
        // character) and the line is blank, the http request has ended,
        // so you can send a reply
        if (c == '\n' && currentLineIsBlank) {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          client.println("Connection: close");  // the connection will be closed after completion of the response
	  client.println("Refresh: 5");  // refresh the page automatically every 5 sec
          client.println();
          client.println("<!DOCTYPE HTML>");
          client.println("<html>");
          // output the value of each analog input pin
          client.println(time2);
          client.println("</html>");
          break;
        }
        if (c == '\n') {
          // you're starting a new line
          currentLineIsBlank = true;
        } 
        else if (c != '\r') {
          // you've gotten a character on the current line
          currentLineIsBlank = false;
        }
      }
    }
    // give the web browser time to receive the data
    delay(1);
    // close the connection:
    client.stop();
    Serial.println("client disonnected");
  }
}


minuteCall((RTCTimerInformation* Sender)time2) {
    Serial.print(RTCTimedEvent.time.minute, DEC);
	time2 = time - 1;
	return();
}

William

Why not just ask the clock what time it is, on each pass through loop? When the second value this time is less than last time, a new minute has occurred? It is not necessary to have that library hold your hand.

I think the library will work if I can pass a value from the the minuteCall function. For example start at 60 minutes, then each time minuteCall is called subtract 1 minute.

I am having trouble visualizing this step.

Code compiles, for now only print minute value when minuteCall is called.

/*
/*  Arduino 1.0+

Count down timer using web display page using digit images.
digit images not implemented yet.

 */
 
 
 
#include <Wire.h>    //  http://arduino.cc/en/Main/Software  included in download
#include <SPI.h>
#include <Ethernet.h>
#include <RTCTimedEvent.h>   // http://code.google.com/p/ebl-arduino/wiki/RTCTimedEvent

int countDown = 60;  //60 Minute countdown timer
int countTime;

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192,168,2,7);

// Initialize the Ethernet server library
// with the IP address and port you want to use 
// (port 80 is default for HTTP):
EthernetServer server(80);

void setup() {
 // Open serial communications and wait for port to open:
  Serial.begin(9600);
   while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }

  Wire.begin();
  
  // start the Ethernet connection and the server:
  Ethernet.begin(mac, ip);
  server.begin();
  Serial.print("server is at ");
  Serial.println(Ethernet.localIP());
  
  RTCTimedEvent.initialCapacity = sizeof(RTCTimerInformation)*1;
  
  //event for every minute
  RTCTimedEvent.addTimer(TIMER_ANY, //minute
                         TIMER_ANY, //hour
                         TIMER_ANY, //day fo week
                         TIMER_ANY, //day
                         TIMER_ANY, //month
                         minuteCall);
  
  
}
  
void loop(){

  RTCTimedEvent.loop();
  
  // listen for incoming clients
  EthernetClient client = server.available();
  if (client) {
    Serial.println("new client");
    // an http request ends with a blank line
    boolean currentLineIsBlank = true;
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();
        Serial.write(c);
        // if you've gotten to the end of the line (received a newline
        // character) and the line is blank, the http request has ended,
        // so you can send a reply
        if (c == '\n' && currentLineIsBlank) {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          client.println("Connection: close");  // the connection will be closed after completion of the response
	  client.println("Refresh: 5");  // refresh the page automatically every 5 sec
          client.println();
          client.println("<!DOCTYPE HTML>");
          client.println("<html>");
          // output the value of each analog input pin
          client.println(countTime);  
          client.println("</html>");
          break;
        }
        if (c == '\n') {
          // you're starting a new line
          currentLineIsBlank = true;
        } 
        else if (c != '\r') {
          // you've gotten a character on the current line
          currentLineIsBlank = false;
        }
      }
    }
    // give the web browser time to receive the data
    delay(1);
    // close the connection:
    client.stop();
    Serial.println("client disonnected");
  }
}


void minuteCall(RTCTimerInformation* Sender) {
  Serial.println("New minute: ");
  Serial.print(RTCTimedEvent.time.minute, DEC);
  //I do not need to keep track of actual minute from RTC.
  //Plan to use this event to subtract 1 minute from the value of countDown (60 minutes).
  
}

William

void minuteCall(RTCTimerInformation* Sender) {
  Serial.println("New minute: ");
  Serial.print(RTCTimedEvent.time.minute, DEC);
  //I do not need to keep track of actual minute from RTC.
  //Plan to use this event to subtract 1 minute from the value of countDown (60 minutes).
  
}

You should not be calling interrupt-dependent functions, like Serial.print() in an ISR, where interrupts are disabled.

Since this function is only called when the minute number changes, why worry about what the minute value was. If you only want to change values once a minute, approximately, using interrupts is the WRONG approach. Learn to read from the clock!

Example that comes with the RTCTimedEvent library includes Serial.print statements in the minuteCall function --example from RTCTimedEvent library:

#include <RTCTimedEvent.h>
#include <Wire.h> //needed for I2C

void setup() {
  Serial.begin(9600);
  
  //set time to 31/12/2010 23:58:50
  RTCTimedEvent.time.second = 50;
  RTCTimedEvent.time.minute = 58;
  RTCTimedEvent.time.hour = 23;
  RTCTimedEvent.time.dayOfWeek  = 6;
  RTCTimedEvent.time.day = 31;
  RTCTimedEvent.time.month = 12;
  RTCTimedEvent.time.year = 2010;
  RTCTimedEvent.writeRTC();
  
  //initial buffer for 3 timers
  RTCTimedEvent.initialCapacity = sizeof(RTCTimerInformation)*3;

  //event for every day
  RTCTimedEvent.addTimer(0,         //minute
                         0,         //hour
                         TIMER_ANY, //day fo week
                         TIMER_ANY, //day
                         TIMER_ANY, //month
                         dayCall);
  
  //event for every hour
  RTCTimedEvent.addTimer(0,         //minute
                         TIMER_ANY, //hour
                         TIMER_ANY, //day fo week
                         TIMER_ANY, //day
                         TIMER_ANY, //month
                         hourCall);
  
  //event for every minute
  RTCTimedEvent.addTimer(TIMER_ANY, //minute
                         TIMER_ANY, //hour
                         TIMER_ANY, //day fo week
                         TIMER_ANY, //day
                         TIMER_ANY, //month
                         minuteCall);
}

void loop() {
  RTCTimedEvent.loop();
}

void minuteCall(RTCTimerInformation* Sender) {
  Serial.print("New minute: ");
  
  Serial.print(RTCTimedEvent.time.hour, DEC);
  Serial.print(":");
  Serial.print(RTCTimedEvent.time.minute, DEC);
  Serial.print(":");
  Serial.print(RTCTimedEvent.time.second, DEC);
  Serial.print("  ");
  Serial.print(RTCTimedEvent.time.month, DEC);
  Serial.print("/");
  Serial.print(RTCTimedEvent.time.day, DEC);
  Serial.print("/");
  Serial.println(RTCTimedEvent.time.year, DEC);
}

void hourCall(RTCTimerInformation* Sender) {
  Serial.print("New hour! ");
}

void dayCall(RTCTimerInformation* Sender) {
  Serial.print("New day! ");
}

Why is this a bad idea? It works in this case.

Why is this a bad idea? It works in this case.

But, not in general. In that case, the print()ing doesn’t actually happen until the ISR ends. In the ISR, the data is buffered. As long as there is room in the buffer, print() will buffer the data and return.

If the buffer gets full, though, print() will block, waiting from room in the buffer. No room will ever appear, because interrupts are disabled in an ISR, and interrupts are required to make more room in the buffer.

In general, Serial.print() in an ISR is a bad idea.