DS1307 I2C RTC DS1307 24C32 Real Time Clock Module for Arduino (Works with Official Arduino Boards)

Pros: Good build quality Woks as supposed

Cons: No pinheads, needs soldering. Does not have pull up resistors, you should add them (2.2k are recommended, but works fine with 1.5k+)

Other: Great product, could only be better with pull up resistors and pinheads in place, to work "out of the box", but it would probably be unnecessary for some people.

Pros: Good quality soldering and pcb. Header is missing but soldering this is not a problem. Clock 1307 works direcly connected to arduino uno. No additional resistors needed. Battery is also working well.

Cons: Two headers purpose not clear,there are two devices on the pcb, clock and eeprom. Eeprom not yet used. Shipping come in esd bag rapped in bubble cover

Other: Good product for good price. Easy connection to arduino uno

Pros: Good quality product. Has good solid soldering. Can be used as clock and for eeprom variable storage. This all via serial interface, only 2 data wires SDA and SCL are needed. Can be directly connected to arduino uno, without extra resitors. For arduino there is special library for this clock chip ds1307. See link http://www.ladyada.net/learn/breakoutplus/ds1307rtc.html for an example.

Cons: The module has two chips , clock and eeprom. I only have used the clock chip. This chip also has small eeprom inside. The two headers are not clear, and neede to be soldered after buying.

Other: Good product. Could be cheaper if eeprom was left out. I do not need this.