Realtime clock during idle?

Forum 2005-2010 (read only) Software Syntax & Programs
1

Hello!
I am working on a project that will require a data log that is saved onto an SD card. I have bought this item (http://tinyurl.com/arduinommc) from ebay, and it will allow me to use a premade mem card (SD) to store files to, however the question I have now is how to make a realtime clock while the Arduino is 'asleep'.
My application will be driving servos, reading analog inputs and various other things, and for this I need a way to monitor what time certain actions occur, but instead of constantly having the arduino on, I need to have it in a low power state until a certain action occurs and while in that low power state, I need to have a realtime clock going with time and date.

I know I will need to use interrupts for this, however I will look into this later.

Thanks for any input!

2

You want an RTC clock chip and crystal. I got one of these recently:
link.

There are plenty of examples of code which work with it - google "arduino DS1307" - and you can add a battery so it will continue to know the correct time when the arduino is powered down, which is very useful. It means you can set the time then dump the time-setting routine, saving a bit of code.

Have a look for RTC or DS1307 in the playground wiki, I think that's where I found out how to work mine.

3

Would this work (only the IC) (http://tinyurl.com/arduinortc) or do I need the 32.768kHz Watch Crystal as well?

Sorry, I could probably find out by reading the datasheet, but my phone doesn't read PDFs well for some reason.

Thanks!

4

No. To implement it properly you need a crystal, and some sort of battery backup. I made my own from parts, and while not as elegant a design as say, the Sparkfun board, it works.

5

You need the crystal. You need a 3v battery for backup too - you can use button cells (I picked up a 3v cell and circuit board mount holder for not much money).

There's a thread in (I think) Bar Spot or maybe FAQ where people list what stores they get stuff from. There might be some tips on where to pick up parts like a clock chip, crystal and battery.
Sparkfun do an RTC breakout board, which is a little circuit board with the chip, crystal and battery on - it'd probably be the easiest solution for you, but not the cheapest.

Edit: here's that thread link. Doesn't look as useful as I remember though.

6

I will buy this (http://tinyurl.com/rtcboard)
from eBay, it should do the trick since it is based on the DS1307 and has the xtal and even a battery holder!