Simple PIC based timer needed, any advice appreciated.

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- 14th August 2010, 00:07
Mr Chris

Simple PIC based timer needed, any advice appreciated.

Im new to this forum so hello everyone! Sorry if this is posted in the wrong place.

I need a simple timer that will pulse for 2 seconds once in every (approx) 24 hours. Physical size must be small as it is to be fitted into existing equipment. Hence why I thought of a PIC solution. 5 volts available and it would need to trigger a miniture relay. Permanently connected to power so would need to reset and then wait a further 24 hours and send a pin high for 2 seconds again.

I know its a simple request but Ive had no luck in finding anything on the web, so if anyone could point me in the right direction that would be very much appreciated!

Chris
- 14th August 2010, 00:44
ScaleRobotics

You could use instant interrupts elapsed timer example. Then look for the flag daychange. Check out this example for 24 hour timer: http://darreltaylor.com/DT_INTS-18/elapsed.html Keep an eye on DaysChange, and you should be able to make it happen.
- 14th August 2010, 23:43
Mike, K8LH

Hi Chris,

Every 24 hours starting when? Starting with power-up?

How precise for the 24-hour interval? Is ±10 secs / day from internal oscillator ok? Or, do you need crystal precision?

Regards, Mike
- 15th August 2010, 10:21
Mr Chris

Timer

Thanks for replies.
I need this to force a hard reset on some telematics equipment. The devices do have built-in timers that can be used for a variety of events, including a system reset. However in practice they fail after a couple of months. This is why we need to have a completely independent timer that we can rely on to do its job. Like I say it would be permanently connected to 5 volts, so would need to start timing on power-up. Also after its 2 second 'on' period, restart again. The 24 hours isnt critical, just an ideal figure, once a day. If this fluctuated and became 22 hours or 26 hours, or a mixture it wouldnt ever be a problem. Neither is the 'on' time 2-5 seconds is fine.
Thanks again.
Chris
- 15th August 2010, 10:48
mackrackit

Quick and dirty

Code:

CNT_1 VAR BYTE CNT VAR WORD HIGH PORTC.4 PAUSE 2000 low PORTC.4 PAUSE 2000 START: FOR CNT_1 = 0 TO 24 FOR CNT = 0 TO 600 HIGH PORTC.4 PAUSE 6000 NEXT CNT NEXT CNT_1 LOW PORTC.4 PAUSE 5000 GOTO START
- 15th August 2010, 20:29
amgen

24 hr tmr

the devices with the 8 mhz int osc are about 1%, (12f283 for example) pretty good timing.
i would blink an led at 1 sec and use the 1 second as a time base. the led just shows that your ckt is doing something.
there are 86400 seconds/day but a var word is only 16 bit - max 65535 count so use 2 second count inc up to 43200.

start:
while count < 43200
high led
pause 1000
low led
pause 1000
count=count+1
end while
outputRSTpin=1
pause 2000
outputRSTpin=0
count=0
goto start

don f
- 16th August 2010, 01:43
Mike, K8LH

Chris,

Would you like to try it on a 55 cent 6-pin 10F200? I just simulated a 63 word program with "cycle accurate" 23:59:58 "off" time and 00:00:02 "on" time. Accuracy will be as good as you can get with the internal oscillator.

Regards, Mike
- 16th August 2010, 11:27
Mr Chris

Mike, that looks interesting. I would like to try that. Using this type of chip how will it perform months down the line. eg in 7 months will I still be getting a 2 seconds 'on' once in 24 hours? What I suppose Im trying to ask is, will it gradually lose time or make time or fluctuate +/- so keepinmg an average of 24 hours?

thanks again
- 16th August 2010, 12:55
Mike, K8LH

Hi Chris,

The example I wrote will maintain a 24 hour cycle as long as it's powered up but the internal oscillator only has a 1% tolerance at room temperature so it will drift. Over a period of several months you might be an hour off from where you started but you should still be getting an interval very close to 24 hours. If that's a problem then you probably should use an 8-pin PIC (12F629, 12F617, 12F635, 12F675, 12F683) and a crystal which should get you accuracy to within a minute or so per year.

Cheerful regards, Mike
- 16th August 2010, 13:16
mackrackit

Mike,
Do you plan on posting the code so Chris can use it or just continue talking about it?
- 16th August 2010, 13:29
Mike, K8LH

Hi Dave,

I sent it to him via PM. Should I post it here for others to see too? It's assembler (yuch!) and it's an isochronous loop, which will look strange even to the assembly language programmers amoung us (lol).

Regards, Mike

<added>

The program outputs a '1' on GP0 for 2 seconds then outputs a '0' for 23 hours 59 minutes and 58 seconds. The GP1 output is toggled at 500-msec intervals for an optional LED "running" indicator. You can verify "cycle accurate" intervals with MPLAB "stopwatch" by placing the simulator breakpoint at the "goto cycle" instruction at the end of the loop.

Code:

;****************************************************************** ;* * ;* * ;* MPLAB: 8.50 (tabs=8) * ;* MPASM: 5.35 * ;* * ;****************************************************************** radix dec include "p10f200.inc" __CONFIG _MCLRE_OFF & _CP_OFF & _WDT_OFF ;--< variables >--------------------------------------------------- delaylo equ 0x10 ; DelayCy() subsystem delayhi equ 0x11 ; DelayCy() subsystem hours equ 0x12 ; Timer sub minutes equ 0x13 ; Timer sub seconds equ 0x14 ; Timer sub ;--< defines >----------------------------------------------------- ;'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ; K8LH DelayCy() subsystem macro generates five instructions ' ; ' clock equ 4 ; 4, 8, 12, 16, or 20 (MHz) usecs equ clock/4 ; cycles/microsecond multiplier msecs equ clock/4*1000 ; cycles/millisecond multiplier DelayCy macro delay ; 12..524298 cycle range movlw high((delay-12)/8)^255 movwf delayhi movlw low ((delay-12)/8)^255 movwf delaylo call uDelay-((delay-12)%8) endm ;****************************************************************** ; main.startup * ;****************************************************************** org 0x000 Startup movwf OSCCAL ; factory INTOSC calibration movlw b'00001000' ; tris GPIO ; GP3 input, all others output clrf GPIO ; clear output latches movlw b'10011110' ; 10011110 ; 1-------, IOC off ; -0------, weak pullups on ; --0-----, T0CS source Fosc/4 ; ---1----, T0SE edge hi>lo ; ----1---, PSA prescale WDT ; -----110, PS prescaler 64 option ; set OPTION reg' ;****************************************************************** ; main.loop * ;****************************************************************** ; alternate 00:00:02 GP0 = 1 (on) and 23:59:58 GP0 = 0 (off) ; cycle DelayCy(500*msecs) ; DelayCy(500*msecs-16) ; movlw 23 ; 23 hours movwf hours ; movlw 59 ; 59 minutes movwf minutes ; movlw 57 ; 58 seconds btfsc GPIO,0 ; GP0 off? yes, skip, else movlw 1 ; 2 seconds movwf seconds ; btfsc GPIO,0 ; GP0 off? yes, skip, else clrf minutes ; btfsc GPIO,0 ; GP0 off? yes, skip, else clrf hours ; timer DelayCy(500*msecs-19) ; 1 sec minus 22 cycle loop time movf GPIO,W ; xorlw 2 ; movwf GPIO ; toggle LED on GP1 pin DelayCy(500*msecs-3) ; movf GPIO,W ; xorlw 2 ; movwf GPIO ; toggle LED on GP1 pin movlw 59 ; W = 59 (mins/secs reset value) decf seconds,F ; decrement seconds btfsc seconds,7 ; negative? no, skip, else decf minutes,F ; decrement minutes btfsc seconds,7 ; negative? no, skip, else movwf seconds ; reset seconds = 59 btfsc minutes,7 ; negative? no, skip, else decf hours,F ; decrement hours btfsc minutes,7 ; negative? no, skip, else movwf minutes ; reset minutes = 59 movf seconds,W ; iorwf minutes,W ; iorwf hours,W ; timer timed-out? skpz ; yes, skip, else goto timer ; branch movf GPIO,W ; xorlw 1 ; movwf GPIO ; toggle GP0 output goto cycle ; loop (new cycle) ;****************************************************************** ; K8LH DelayCy() subsystem 16-bit "uDelay" timing subroutine * ; * nop ; (delay-12)%8 == 7 entry point nop ; (delay-12)%8 == 6 entry point nop ; (delay-12)%8 == 5 entry point nop ; (delay-12)%8 == 4 entry point nop ; (delay-12)%8 == 3 entry point nop ; (delay-12)%8 == 2 entry point nop ; (delay-12)%8 == 1 entry point uDelay incf delaylo,F ; subtract one 8-cycle loop skpnz ; borrow? no, skip, else incfsz delayhi,F ; done? yes, skip, else goto uDelay-3 ; do another 8-cycle loop retlw 0 ; ; * ;****************************************************************** end
- 16th August 2010, 13:39
mackrackit

I think you should post it for others that are following along. How many times have you looked for a solution to a problem and when you think you found it the solution was never posted??

Kinda a pet peve of mine.

But it is up to you.
- 17th August 2010, 00:14
Mr Chris

Mike, thanks for that. I will hunt down and dust off my programmer and give this a whirl. Might just do the trick. Keep you posted and thanks again.
Chris
- 3rd December 2011, 09:17
Dagwood

Re: Simple PIC based timer needed, any advice appreciated.

Hi All,Very new to Pic Programming and very new to your forum. I found this thread searching Google for ideas on progrmming a PIC on a 24hour cycle. Ok the problem, I have a JDM programmer and when I try to write to a 10F200 PIC all I get is, [IMG]file:///C:/DOCUME~1/BENSHE~1/LOCALS~1/Temp/msoclip1/01/clip_image001.png[/IMG]I have tried running it from the ZIF sockets and the off board connectors????Am stuck now??? Any ideasCheersDagwood
- 22nd January 2012, 04:06
Demon

Re: Simple PIC based timer needed, any advice appreciated.

Moved from Schematics.

Robert