Hi Antonio

>Can someone tell me about a RTC to use in a data logger, i need one small
>as possible and with built in battery ?
>
>Thanks.

Think that the most compact RTC in the market with built in battery is
Dallas DS-1994. You get RTC, xtal, battery and 512 byte BBRAM all in a
stainless steel case of 16mm diameter by 5mm thick. Looks like a big coint
cell battery.

Any other RTC will need (at least) external battery or, if including
battery, it will be a 24 pin DIP block 6mm high.

But there are some warnings on using this device:

1) Clock is just a 5 byte binary counter incrementing at 256 times per
second. You have to write code to calculate
year/month/day/hour/minute/second from that mess.

2) The device is interfaced using the Dallas 1wire protocol. You will have
to write code to manage the protocol. The good news is that it'll only get
one I/O pin from your CPU.

3) There is no "RTC only" version and if you don't need the 512 bytes of
BBRAM you will have to pay for them anyway. But if that is enought for your
data logger you can build the whole thing with the DS-1994 and a PIC. Cost
in Spain for 100pcs is about $10 each.

May be you can find someone who share the PIC code for this. Good luck !.



Luis Fernandez Cormenzana
RadioBit Sistemas, S.L.
        Vehicle fleet control systems
        Patrol presence controllers

Fax/Tel:+34-6-585 64 57
e-mail: radiobit@dragonet.es
http://www.dragonet.es/users/radiobit