Using Pic as a digital clock/timer. How accurate?

[fazan83]

Thanks Fazan for the code but one thing i didn't understand is how do i get the actual seconds by simply counting? if you count from 1 to 60 does it mean its 1 to 60seconds? can you clarify how you convert from the simple execution time for the count to actual seconds.
Thanks a lot

How accurate it is depend on the speed of oscillator that u use.

[sayzer]

Also, the ambient temp is the most effective factor.

You can get a slow running or fast running clock ticks depending on the temperature of the environment in which your PIC is running. (ambient temp)

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[Acetronics2]

Hi, Rocky

I just built Thermo-baro-clock with a MS5534 sensor.( 16F876 ) the clock is driven by a 32.7... khz "clock crystal" connected to RC0,RC1 pins and using TMR1 ovf interrupt.

The only way to adjust reading is to trim the TMR1 preset ( 32768 ...in theory ). an adjustable capacitor parallelled to one of the xtal load caps could also help a bit.

Possible also to use two pushbuttons to inc/dec the TMR preset value, you then store in the EEPROM ... but do not forget to limit the trim range !!!

But as always ... no simple automatic trimming.

Absolute references will always be our main headaches ... cause there's none naturally existing !!!

best regards
Alain

[rocky79]

Thanks guys for all the help and links. I found a chip that does all the hard work for me on top of that it is featured with 2 alarm settings.
http://pdfserv.maxim-ic.com/en/ds/DS3232.pdf

I will give it try and will see how it goes.
Thanks again

[SteveB]

I've used the clock only version of the chip (a temp. compensated oscilattor) and can attest to it's accuracy. It was hard to get a hold of at the time, though supply might be better now.

SteveB

[rocky79]

I've used the clock only version of the chip (a temp. compensated oscilattor) and can attest to it's accuracy. It was hard to get a hold of at the time, though supply might be better now.

SteveB

Hello Steve,
I am using the RTC DS3232 from dallas. you said you have used it before. Can you share your picbasic code? I am having trouble setting the time.
when i read the time and date. I get them all as 4.
Here is mine:
'Using the pic 16f630

include "modedefs.bas"
define OSCCAL_1k 1
CMCON=%0000011' Turn off comparator module


minutes var byte
hours var byte
day var byte
date var byte
month var byte
year var byte

reset Var PORTC.0

rtcyear var byte
rtcday var byte
rtcmonth var byte
rtcdate var byte
rtchour var byte
rtcmin var byte
rtcsec var byte

' Set initial time to 8:00:00AM 07/16/99
rtcyear = $99
rtcday = $06
rtcmonth = $07
rtcdate = $16
rtchour = $08
rtcmin =0
rtcsec =0

startbigNums con 2
endBigNums con 3
clrLCD CON 12
backLightOn con 14
backLightOff con 15
cursorPos con 16
enter con 10
bell con 7
b2 var byte
CONTL CON %01101000


Low reset 'reset the RTC
input reset ' undo reset..basically it puts pin reset at high impedance

'Set the time
I2cwrite PORTC.2,PORTC.1,CONTL,$01,[rtcmin] 'minutes
I2cwrite PORTC.2,PORTC.1,CONTL,$02,[rtchour]'hours
I2cwrite PORTC.2,PORTC.1,CONTL,$03,[rtcday] 'day
I2cwrite PORTC.2,PORTC.1,CONTL,$04,[rtcdate]'date
I2cwrite PORTC.2,PORTC.1,CONTL,$05,[rtcmonth]'month
I2cwrite PORTC.2,PORTC.1,CONTL,$06,[rtcyear] 'year


pause 10
'Low reset
'input reset
I2cread PORTC.2,PORTC.1,CONTL,$01,[minutes]
I2cread PORTC.2,PORTC.1,CONTL,$02,[hours]
I2cread PORTC.2,PORTC.1,CONTL,$03,[day]
I2cread PORTC.2,PORTC.1,CONTL,$04,[date]
I2cread PORTC.2,PORTC.1,CONTL,$05,[month]
I2cread PORTC.2,PORTC.1,CONTL,$06,[year]

serout2 0,16780,[clrLCD,"Time",hex hours,":",hex minutes,enter,_
"date:",hex date,"/",hex month,"/",hex year]
end

[SteveB]

Bad wording on my part. What I ment was that I have used one of the temperature compensated oscillators (the DS32kHz, not the DS3232 RTC) with other RTCs and as an input to the PIC timers, and they worked well. I'll have a glance at you code and the Datasheet to see if I can spot anything.

With other DSXXXX RTCs, I have seen the need to set some of the registers to appropriate setting before things work correctly. So that is one place to start.

I'll get back if I see anything.

SteveB