DS1307
https://www.sparkfun.com/datasheets/Components/DS1307.pdf
https://inline.inajob.tk/img/twitter-5643382/DS1307/4ec68393-dcf9-11ed-ae67-fe51f6f5a13e#.png
- 32.768kHzの水晶があれば後は汎用部品
- VCCは5V、VBatは3V(2-3.5V)