Why don't you try an interrupt driven timer then it will execute the code in
your main loop once every  20mS /1Sec/1Min ect... needs a variable for each
group and a flag register to signify its time to do each activity. All runs
of the system clock and uses TMR0 or TMR1 heres a little snippet from the
ISR that sets up a tick.

;------------------------ INTERUPT
PROCESS--------------------------------------
TMR1_ISR            
;------------------------ An interrupt (based on 4MHz crystal)--------------
;------------------------TMR1H (F3)  TMR1L (CE)
25mS----------------------------
;------------------------TMR1H (CF)  TMR1L (2B)
100mS---------------------------
;------------------------TMR1H (FB)  TMR1L (21)
10mS----------------------------
	BCF		PIR1,TMR1IF		; CLEAR INT FLAG
	BSF		TICK			; SET 10ms FLAG
	MOVLW	0F3h			; RELOAD VALUE FOR TMR1H (10ms)
	MOVWF	TMR1H			; SAVE IN REG
	MOVLW	0CEh			; RELOAD VALUE FOR TMR1L
	MOVWF	TMR1L			; SAVE IN REG
	MOVLW	B'00110001'		; PSCALE 8 INT AND ON AND SYNC
	MOVWF	T1CON			; FIT IT
	RETURN

Steve

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
solarwind
Sent: 16 August 2009 03:31
To: PICLIST
Subject: [EE] How to generate a 1000 Hz pulse? (and PIC timers)

To get accurate speed readings for my bicycle speedometer project, I
have to count how long it will take the wheel to turn rather than how
many times it has turned in x seconds. I want a 1 second speed update
rate so to go about it, I need to count how many milliseconds it takes
for the wheel to spin once. That way, I can get an accurate speed
reading.

So, I need some way to generate and count a 1000 Hz pulse. How would I do
that?

One idea is, I could use a (16 bit) timer on a PIC (16 bit would allow
for a 65 second count using a 1 KHz pulse) and count up (can a PIC
timer count up (not down)?). I can use an external crystal for the
timer and divide it down to 1000 Hz (can I divide an external clock
signal down?).

That way, once I have the timer counting at 1000 Hz, I can read and
reset the timer every time the reed switch is pulsed. For example, if
it takes 0.764 seconds for the wheel to spin once, the timer would
read 764 just before being reset for the next count. I could use 2
magnets on opposite ends of the wheel for greater accuracy (and
balance).

Would this work?

-- [ solarwind ] -- http://solar-blogg.blogspot.com/
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