A few months back, I put together an Arduino with a datalogger shield (Adafruit Assembled Data Logging shield for Arduino : ID 1141 : $13.95 : Adafruit Industries, Unique & fun DIY electronics and kits), to measure solar irradiance at a test site.
It worked fine for a while, but then one day, I got this:
Datetime Solar Irradiance
6/23/2015 14:54 815.43
6/23/2015 15:25 427.25
6/23/2015 15:56 307.62
6/23/2015 16:28 0
6/23/2015 16:59 0
6/23/2015 17:30 0
6/23/2015 18:02 0
6/23/2015 18:33 8.54
6/23/2015 19:04 0
6/23/2015 19:35 0
6/23/2015 20:06 0
6/23/2015 20:37 0
6/23/2015 21:08 0
6/23/2015 21:39 0
6/23/2015 22:11 0
6/23/2015 22:42 0
6/23/2015 23:13 0
6/23/2015 23:44 0
6/24/2015 0:15 0
6/24/2015 0:46 0
6/24/2015 1:17 0
2165/165/165 165:165:85 0
2165/165/165 165:165:85 0
2165/165/165 165:165:85 0
2165/165/165 165:165:85 0
As you can see, after 1:17 am, the timestamp just goes to 2165/165/165 and on and on it goes. I reconfigured the RTC and re-uploaded the logging sketch last week...worked fine for a few days, and then the timestamps went to 2165 again.
The Arduino is in a box that nobody touches. The last time it went to 2165/165/165 was at 5 am, so nobody was tampering with it.
Any ideas at all what might be causing this?