Improving accuracy

Thanks to the readonly old Arduino forum I noticed only today that the author of the DCF77 code I am currently using published an update, nearly a year ago.

He wrapped it in a nice library, which makes it a lot easier to use. Sadly it doesn’t work on version 1.0 of the Arduino UI, so I reverted to version 0022 for now. There are newer “old” versions of the UI, but I had this version still installed.

This is the example from the library:

#include "Dcf77.h"
 
Dcf77 dcf77(0); 
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  const char *v = dcf77.getDateTime();
  if (strcmp (v,"DCF77POLL") != 0) {
    Serial.println(v);  
  }
}

The library takes care of parity and plausability checks, so I don’t have to worry about that anymore. The downside is that it produces the current time far less frequent than the code I’m using now, but when it returns one it is correct.

I’m still leaning toward adding a realtime clock to the clock. This way I can rely on the RTC for the current time and correct it now and then when I get a signal from the DCF receiver.

Circuit board for the wordclock

Yesterday I was playing with Fritzing to create a circuit board for the wordclock. Building it on the breadboard was easy, but the auto routing on the PCB-layout drove me nuts. Today I tried it again, loaded the file, repositioned the components on the circuit board a little and guess what … it worked on the first try. This is how the circuit board in the next version of the wordclock may look like:

It is designed for an Arduino Mini Pro, which is by far the cheapest Arduino variant I could find and which is sufficient for this purpose. U1, U2 and U3 will hold the 74HC595 ICs, J3, J4 and J5 will connect the LEDs. J2 is the connection for the DCF77 receiver.

I guess next I’ll have to learn how to etch my own circuit boards.

Breakthrough

This evening I managed to get a breakthrough while I was working on the wordclock. The clock kept showing a completely wrong time now and then, followed by the correct time a minute later.

So I loaded the test program for the DCF receiver again and monitored the output on the serial console over a longer time (one or two hours or so). I noticed that the receiver actually gave incomplete information once in a while. To rectify this I did two things: Continue reading Breakthrough