DS1307 sqw as interrupt acting strangely?

Projects Networking, Protocols, and Devices
1

Hello all... I am attempting to use the Sparkfun DS1307 sqw output as an interrupt to ensure that some timers are checked once a minute. I have it working, however the I am getting multiple reads on the interrupt pin. Here is the applicable code

#include <Wire.h>
#include <DS1307RTC.h>
#include <Time.h>
volatile boolean sqwinterrupt = false;

void setup() {
  pinMode(3, INPUT_PULLUP);  // Used as interrupt pin for DS1307 sqw output @ 1Hz
  // This sets the sqw of the ds1307 to 1Hz, used as interrupt to check the times to see if outputs need updating
  Wire.begin();
  Wire.beginTransmission(0x68);
  Wire.write(0x07);  // Goto the sqw register
  Wire.write(0x10);  // binary B00010000 sets sqwenable to 1 and rs0 and rs1 to 0
  Wire.endTransmission();
  attachInterrupt(1, sqwInterrupt, FALLING);
}

void loop() {
t = now();
if (sqwinterrupt == true) {
    Serial.print("Sqw:");
    Serial.print(hour(t));
    Serial.print(":");
    Serial.print(minute(t));
    Serial.print(":");
    Serial.println(second(t)); 
    sqwinterrupt = false;
   if (second(t) == 0) {  // Only need to check the timers once a minute
     checkTimers();
     Serial.print("Timers checked at: ");
     Serial.print(hour(t));
     Serial.print(":");
     Serial.print(minute(t));
     Serial.print(":");
     Serial.println(second(t));
   }
  }

/*************************
 ***  sqwInterrupt()  ****
 *************************/
 void sqwInterrupt() {
   sqwinterrupt = true;
 }

This gives me an output like so:
Sqw:21:46:57
Sqw:21:46:57
Sqw:21:46:57
Sqw:21:46:57
Sqw:21:46:58
Sqw:21:46:58
Sqw:21:46:58
Sqw:21:46:58
Sqw:21:46:58
Sqw:21:46:59
Sqw:21:46:59
Sqw:21:46:59
Sqw:21:46:59
Sqw:21:47:0
Timers checked at: 21:47:0
Sqw:21:47:0
Timers checked at: 21:47:0
Sqw:21:47:0
Timers checked at: 21:47:0
Sqw:21:47:0
Timers checked at: 21:47:0
Sqw:21:47:0
Timers checked at: 21:47:0
Sqw:21:47:1
Sqw:21:47:1
Sqw:21:47:1
Sqw:21:47:1
Sqw:21:47:1
Sqw:21:47:2
Sqw:21:47:2
Sqw:21:47:2
Sqw:21:47:2
Sqw:21:47:2
Sqw:21:47:3
Sqw:21:47:3
Sqw:21:47:3

Any ideas on why this might be? I guess I could use a flag to check that the once the timers are checked to skip until the 1 second mark... but that seems unnecessary
Any help would be appreciated and thanks in advance!

2

I have discovered the source of my problem. I am using interrupt 1 on pin 2 to read the tachometer of a 12v computer case fan. When the fan is on, it is injecting noise or something that is being read on pin 3. I currently have the computer fan being powered by a bench power supply, and the arduino powered from USB. Should i tie the grounds together or something to reduce the noise?

3

OK, seems that my thinking cap was able to solve the problem. I used an 8v regulator (using 317 variable regulator set to 8v) powered from the 12v bench supply. I ran the arduino off of the 8v using the vin and gnd pins. This solved the noise issue for me, and now everything is reading correctly. I would still appreciate if someone could tell me what kind of bad things might happen if i tied the ground of the 12v bench supply and the ground of the arduino when its powered by usb. Would this cause my computer to burst into flames? I'd rather not test such a theory :stuck_out_tongue: