3V RTC chip?

I was working on a little clock project that runs off a 3v coin battery with the arduino bootloaded at 8MHz until I realized that the ds1307 has a 4.5V minimum. It looks like the 1302 doesn't seem to be similar enough to the 1307, I can't tell if it would still work.

The ds3231 seems to have 3v operation but I can only find it already placed onto a board. Because of this I don't know if the boards are meant for 5v only(they seem to have an entire extra IC so who knows whats going on there). I also don't know if I can interface the IC by itself with the arduino like I can with the 1307. I would really like to have a lone chip, my 3v projects are usually meant to be pretty compact. I don't have any issue with SOIC packages.

Is it a good idea to be using a ds3231 without a breakout board? What is that little extra chip for? Is there something else better to try?

You have not linked to the breakout board your looking at but I'm sure the extra chip will probably be a small memory chip. The DS1307 has a small amount of built in memory for general use where the DS3231 does not, so vendors tend to put a little bit of memory on there breakout boards.

I have a few projects using the DS3231 and apart from the usual decoupling capacitor, pullup resistors on the I2C lines and a battery (optional) you don't need anything else.

I times past you could get the DS3231 in an 8 pin DIP package and when that was phased out you could still get an 8 pin SMT version but it looks like all you can get now is the 16 pin surface mount package.

That little extra chip is EEPROM. It was added to DS1307 boards on Ebay. When making a DS3231 module, they decided to add also the EEPROM.

http://www.ebay.com/itm/371166867487

There are many 3v3 RTC chips, apart from them mostly being SMD devices and therefore a bit hard to solder (arguably) there's no reason you can't use them directly, no need for a breakout board.

I'm not at my normal computer now but if you get stuck I can find some examples later.


Rob

when the breakout board has a battery and the board and the battery cost less than just the battery…

in this case, the board I linked is tiny and the battery is tiny as well. not sure of the life expectancy of the battery.

the smt work is done and this is ready to plug in.

definitely not as clean looking as making your own board with the battery holder and the RTC.