Blink without delay and millis but with the DS1307 :)

Using Arduino Programming Questions
#1

I want to use a DS1307 RTC in a home automation project to do certain time based things. I have a small DS1307 board and have managed to make it work with various sketches that I’ve found online. This code was very handy → RTC1307 - Real Time Clock - Combustory
Now I thought lets try to make a sketch like the blink without delay example but using the data from the DS1307.
But I’m getting nowhere, I don’t really have a clue how I should make this sketch… Anyone that can help me?
I’ve made the following sketch, which does not work.

/*
 Blink without delay using a DS1307
 Led blinks once every second.
 */

#include <Wire.h>
const int DS1307_I2C_ADDRESS = 0x68;

const int led =  13;      // the number of the light pin
int ledState = LOW;

byte second, minute, hour;

// Convert binary coded decimal to normal decimal numbers
byte bcdToDec(byte val)
{
  return ( (val/16*10) + (val%16) );
}

void getDateDs1307()
{
  // Reset the register pointer
  Wire.beginTransmission(DS1307_I2C_ADDRESS);
  Wire.send(0x00);
  Wire.endTransmission();

  Wire.requestFrom(DS1307_I2C_ADDRESS, 3);

  second     = bcdToDec(Wire.receive() & 0x7f);
  minute     = bcdToDec(Wire.receive());
  hour       = bcdToDec(Wire.receive() & 0x3f);
}

void setup() {
  Wire.begin();
  pinMode(led, OUTPUT);      
}

void loop(){

  getDateDs1307();
  int time1 = second;

  getDateDs1307();
  int time2 = second;
  if (abs(time1 - time2) > 1)
  {
    if (ledState == LOW) 
      ledState = HIGH;
    else
      ledState = LOW;

    // set the LED with the ledState of the variable:
    digitalWrite(led, ledState);
  }
}
#2 
  getDateDs1307();
  int time1 = second;

  getDateDs1307();
  int time2 = second;
  if (abs(time1 - time2) > 1)

time1 is nearly always going to equal time2 - 99.99999999999999% of the time. Your if test will hardly ever be true.

#3

I'm not sure I understand the point, but your code might work better like this:

...
int lastTime = -1;

void loop(){

  getDateDs1307();
  int time1 = second;
  if (abs(time1 - lastTime) > 1)
  {
    if (ledState == LOW) 
      ledState = HIGH;
    else
      ledState = LOW;

    // set the LED with the ledState of the variable:
    digitalWrite(led, ledState);
    lastTime = time1;
  }
}

I hope this helps,

Brad.

#4

Ha, that works. These simple things sometime look so difficult :roll_eyes: Thank you.

#5

Note that that only works for intervals under 60 seconds. If you want longer intervals you could calculate the time of day in seconds:

unsigned long time1 = ((hours*60L)+minutes)*60L+seconds;

This would let you time intervals up to half a day (43,200 seconds).

#6

That's interesting, thanks for the info.

#7

Bajdi: Ha, that works. These simple things sometime look so difficult :roll_eyes: Thank you.

No problem. One more suggestion for next time: If all you're trying to do is switch ledState from HIGH to LOW, you can do something like this:

ledState = !ledState;

I know you were using the example code, I just thought I'd share a simpler way (less typing too ;-) )

(the example code structure of the if/else statement works better in many real world cases where, for example, you might want to do something - like controlling a pump - as well as toggling the LED's on and off)

Brad (KF7FER)

#8

This thread is a treasure trove of an example how to do something of an action with DS1307 other than set a clock, which is the echo-chamber Internet is full of. You guys got me to the square two! Square three will be to have DS1307 control a one of the servos at a set time intervals.

#9