Comparison of four real-time clocks

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This is my last hand-wired prototype board. Now that I have figured out how to make inexpensive PCB boards quickly and easily (eight days and US$  22), I am not making any more by hand. I still will use a breadboard, however, on occasion. Board-level simulation tools aren't quite available or easy enough to use yet.

The Accuracy Test Software

To test the RTCs automatically, I constructed a program that first sets each clock and then, every 10 minutes, logs the time differences and the calculated parts per million (ppm) between the RTCs and the NTP-corrected Raspberry Pi clock into a MySQL database. All this was done completely on the Raspberry Pi. The clock on the Raspberry Pi is not very accurate but the NTP daemon will correct the time on a regular basis, making the PI a pretty good clock, as long as you are connected to the Internet.

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