I recently bought a Tiny RTC module and experienced difficulties too. This post helped me a lot ! Thank you !
Nevertheless, I don't want to apply on board modifications, so I have found another way to make it work (without exploding batteries
I am here to share my own experience on this module and I came with some questions ...
First, concerning the oscillator and the ground thing, it seems from DS1307 datasheet itself (http://datasheets.maximintegrated.com/en/ds/DS1307.pdf
) that oscillator must be attached to ground (figure 2, p7) in order to be isolated from "RF generating signals". jonwwo was right (compliant with specs). End of story.
Then, if i understood well, this module is dedicated to work with rechargable battery only. I didn't had any, so I tried with a non rechargable one : that was not working. But if I powered up VCC pin, it works. Question 1 : Should I understand that powering VCC is mandatory ?
After that, I removed battery, and let VCC connected (from Arduino). That was working well, but when arduino was disconnected, RTC module was switched off and I lost current time. I could have expected that.
Finally, I powered up RTC module from external power source (9V battery through LM7805). Of course, Arduino powered or not, I keep current time and further request to time returns correct answer. Question 2: why powering VCC with external power source helps keeping time memory, while using a little CR2032 cell does not keep it ?
Given the diagram already posted (http://www.emartee.com/Attachment.php?name=42059.pdf
), it should be the same to me : VBAT pin is connected both to battery and VCC. CR2032 and LIR2032 voltage is quite the same, am I wrong ?
Now, I think I will keep an external power source connected to VCC to keep RTC module running, but it sources about 1.8 mA, while spec says that it sources only 5nA from battery. I am worried by this high consumption. Question 3 : Is there a way to decrease this ?
Anyway, this cheap module seems to do the job, but is quite hard for a beginner to make it work. And I guess it will become harder if I want to decrease current. We'll see ...