How to Keep track of time?

jaikumar · Joined: 15 Dec 2006 Posts: 109

I need to keep track of a lamp operating time. Have to save values in-between power cuts. What will be the best way to do this?

Hope someone can give me ideas.

Thanks and Regards.
Jai.

Jerson · Joined: 31 Jul 2009 Posts: 122 Location: Bombay, India

1. Use an RTC chip like the DS1307
2. Implement a firmware timer code along with a power fail early warning interrupt that you use to save the time values to the EEPROM
_________________
Regards
Jerson Fernandes

Wayne_ · Joined: 10 Oct 2007 Posts: 681

The last post brings up the question of:-
Does the PIC loose power during the power cut or do you monitor the power outage another way ?

I assumed the PIC was running on battery or something.

If your PIC has RTCC built in then just use that. Also what accuracy do you need ? Second, ms ?

jaikumar · Joined: 15 Dec 2006 Posts: 109

I don't want to use RTC. Don't need to be very accurate. The Clock is 4Mhz crystal.
I have seen other posts on this issue. Want to know whether a diode and huge cap supply for the pic alone and a voltage divider sample idea.Save to internal eeprom. will it work? have to save 4 bytes.

vsmguy · Joined: 13 Jan 2007 Posts: 91

You would not need an RTC - there is a thesis on the net about getting precise 1sec delays in a PIC.

It's in PDF format.

How you manage to keep the PIC powered is at your discretion.

Wayne_ · Joined: 10 Oct 2007 Posts: 681

WIth a cap you could proberbly keep the PIC running for a little while when the power goes off, depending on current draw.

I assume then you will not be powering the PIC whilst the power is off?
Are you expecting the cap to keep the pic powered up whilst the power is off or do you just want it to keep it on for long enough to store the values ?

jaikumar · Joined: 15 Dec 2006 Posts: 109

Are you expecting the cap to keep the pic powered up whilst the power is off - I ONLY WISH.
No Just Long enough to store the 4 byte values on the internal eeprom of pic.

Wayne_ · Joined: 10 Oct 2007 Posts: 681

So what are the 4 bytes ?

The pic will have no knowledge of how long it was off and it will not be able to work out how long it was off unless you have some extenal timer.

Each time the pic powers up will you be setting the time info on it somehow?

You will only be able to monitor how long the pic was on for each time. This will not tell you how long the power was off.

vsmguy · Joined: 13 Jan 2007 Posts: 91

This is going to get complicated.

As I said at the beginning - How you manage to keep the PIC powered is at your discretion.

This is a forum for the CCS compiler.

Keeping the PIC powered has nothing to do with it.

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

vsmguy · Joined: 13 Jan 2007 Posts: 91

A good way to power the PIC would be to have a LDO connected to the regular 9V battery via a relay/FET that switches when there is no external power.

This would give the PIC all the backup it would ever need.

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

Here are some other threads on this issue, including formulas:
http://www.ccsinfo.com/forum/viewtopic.php?t=38936
http://www.ccsinfo.com/forum/viewtopic.php?p=30962
http://www.ccsinfo.com/forum/viewtopic.php?t=25733
http://pic-c.ccsinfo.com/forum/viewtopic.php?p=23543

Humberto · Posted: Thu Jul 08, 2010 7:14 pm