As I mentioned in a previous post, I was not enormously satisfied with the accuracy of the DS1307 clock module that I got from China. It was hard to argue with the less than three dollar price tag, but I was hoping that the accuracy might achieve 20ppm (less than two seconds of drift per day). My measured drift was over ten times that, about 25 seconds per day. Ungood.
Toward that end, I picked up a different clock module based upon the DS3231 chip. I didn’t have much time to play with it, but I did power it up.
A couple of quick notes:
- It seems to have a dedicated 32KHz output, but it doesn’t run when solely on battery power.
- The rise time of the 32kHz signal is pretty slow.
- The duty cycle of the 32Khz signal is significantly below 50%.
- The frequency as reported by my (not terribly accurate) oscilloscope’s built in frequency meter seems very close to the nominal 32768 Hz signal.
When I get time tonight, I’ll test it against my GPS and see what really works. My initial impression? Positive. If you care about even reasonable accuracy, paying a couple of bucks more for a clock module will probably be a good idea.