Mmm.., using "sleep" with watchdog timer seems useful for other project
than a datalogger.  I need  accurate timestamp and I dubt that precision,
for example in two months, will be into 5 minutes range.
When my logger will be mounted in an external meteo-station, it will be
submitted to a
temperature interval of 20-30 C a day in some seasons. I think that will be
difficult to have an accurate
timing with watchdog oscillator that isn't stable as a crystal osc.

However, this method seems to be useful for general purpose use or for a
shorter time interval, so I will test this interesting method!

DS1620:
with honesty, if I will use 32Khz solution I will prefer a DS1721 (I2C
protocol)
that have about half the price and is  technically more stable than the
"old" types 1620
and 1820. Another feature, if I'm not wrong, is high-res temperature data
stored in two byte.
Measuring temp. in high-res mode with DS1620 needs to store four bytes in
logger eeprom, with half capacity of measurements ( in my logger 8Kbyte
rather than 16Kbyte).


Now, many thanks for your suggestions!
(also to Byron A Jeff  for the DS1620 code)


----- Original Message -----
From: "Spehro Pefhany" <speff@INTERLOG.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: 7 febbraio, 2002 18.06
Subject: Re: [EE]: 16F84 Datalogger - current consumption


> At 10:40 AM 2/7/02 -0600, you wrote:
> >I use the watchdog.  Set it for max delay (around 2.3 seconds nominal)
and
> >go to SLEEP.  The watchdog will wake you up.  In mine I do two
consecutive
> >SLEEPs, so I get a new reading a little more than once every 5 seconds.
> >
> >Of course this won't do you a lot of good if you need to log anything
> >resembling an accurate timestamp, but I have gotten several months out of
> >three AA cells this way.  Mine was a 16F84 and DS1620, by the way - I
> >think a 1620 would be fine with a slow clock, and it's only two more pins
> >than an 18S20 and simpler software.
>
> ISTR someone came up with a clever way of calibrating the WDT so that you
> could get better accuracy without resorting to an external RTC.
>
> Best regards,
>
> Spehro Pefhany --"it's the network..."            "The Journey is the
reward"
> speff@interlog.com             Info for manufacturers:
http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:
http://www.speff.com
> 9/11 United we Stand
>
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>

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