PIC Delay question - Electronic Circuits Projects Diagrams Free

Trevors · 21st April 2008, 05:34 PM

Hello everybody,
I'm trying to drive a stepper motor that I got from a faulty flatbed scanner. I am driving it via a ULN2004. The ULN2004 is being driven from the outputs of a 4154(4 to 16 decoder) I,m using RB1,2,3,4. I had this set up for another project and chose to use the same code. I've managed to get it to step but cannot generate a delay short enough to make it run continuosly. If I use two loops and load both registers with 01h the delay is too long. If I use one loop and load the register with FFh ,the delay is too short and the motor doesn't run at all. Please help with my code. See attached file. Help appreciated

ericgibbs · 21st April 2008, 06:05 PM

Quote:

Originally Posted by Trevors

Hello everybody,
I'm trying to drive a stepper motor that I got from a faulty flatbed scanner. I am driving it via a ULN2004. The ULN2004 is being driven from the outputs of a 4154(4 to 16 decoder) I,m using RB1,2,3,4. I had this set up for another project and chose to use the same code. I've managed to get it to step but cannot generate a delay short enough to make it run continuosly. If I use two loops and load both registers with 01h the delay is too long. If I use one loop and load the register with FFh ,the delay is too short and the motor doesn't run at all. Please help with my code. See attached file. Help appreciated

Hi Tervor,
Does this help.?

http://www.piclist.com/techref/picli...egen/delay.htm

Trevors · 21st April 2008, 06:25 PM

Txs Eric,
Will take a look at it.

ericgibbs · 21st April 2008, 07:06 PM

hi trevor,

Just a thought, did you delete the delays you had in the 4514 mux, when driving the LED's???

If you have a spare analog pin, its easy to connect a pot and control the stepper rate by using the pot.

donniedj · 22nd April 2008, 01:59 AM

Standardize your delays. Make a set for micro seconds, milli seconds, and seconds similar to my code below.

Code:

Set LED
Call usec100
Call usec100
Clear LED
Call usec100
Call usec100
Loop

movlw .50
movw milli_time        ; Load milli_time only once because it is persisted into milli_time_temp.
Set LED                ; A.K.A non-volatile.
Call milli_delay
Clear LED
Call milli_delay
Loop

Code:

USEC_10:
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	RETURN
USEC_20:
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	GOTO	$ + 1
	RETURN
USEC_100:			;----FORMULA--4MHZ CLOCK---------
	MOVLW	.31		;  [3(CNTJ-1)+2] + CHANGE
	MOVWF	CNTJ		;  CHANGE = 8 USEC
	DECFSZ	CNTJ, F		;  [3(CNTJ-1)+2] + 8
	GOTO	$ - 1	        ;--------------------------------
	NOP
	NOP
	RETURN

MS_DELAY:
	MOVF	MILLI_TIME, W    ;---------------------------------------
        MOVW    MILLI_TIME_TEMP  ;MILLI SECOND DELAY
MS_LOOP	MOVLW	0XA4             ;DELAY = X MILLI-SECOND (4MHZ CLOCK).
	MOVWF	CNTJ             ;---------------------------------------
	DECFSZ	CNTJ, F
	GOTO	$ - 1
	MOVLW	0XA4
	MOVWF	CNTJ
	DECFSZ	CNTJ, F
	GOTO	$ - 1

	DECFSZ	MS_TIME_TEMP, F	;IF COUNTER ENDS,
	GOTO	MS_LOOP		;ELSE- REPEAT
	RETURN			;THEN- EXIT LOOP

Trevors · 22nd April 2008, 12:48 PM

Hi Eric,
Yes, I still have the same delays. Don't have any analog pins though. Using a 16F84a, but I have purchased a 16F628a. Going to start using that soon. How would I implement the pot idea?

Txs for those delays Donniedj. I'm sure those will come in handy.

ericgibbs · 22nd April 2008, 01:08 PM

Quote:

Originally Posted by Trevors

Hi Eric,
Yes, I still have the same delays. Don't have any analog pins though. Using a 16F84a, but I have purchased a 16F628a. Going to start using that soon. How would I implement the pot idea?

Txs for those delays Donniedj. I'm sure those will come in handy.

hi Trevors,
Connect a variable resistor say a 5K0, one end of the pot to 0V and the other to the +5V rail, wiper to the analog pin of the PIC.

Use the ADC value as right justified to get 0 thru d'1023,, call the value say Dv.

To get a 'useful' value of Dv and to set the 'minimum' delay value of Dv do this:

Delay= (Dv * multiplier) + shortest delay required.

Assume for explanation that Dv is 0 from the ADC registers.
then Delay = shortest delay time required

Assume that Dv is 1023 from the ADC registers
then Delay = (1023 * multiplier) + shortest delay === Longest delay time.

You will have to determine the values of the 'multipler' and 'shortest delay required' to suit your motor and application.

I would start with values of 'multiplier' = 1 and 'shortest delay' =1000

Once you have determined the max and min value, as the speed pot is adjusted, the ADC output is read and the Delay calculated from this formula and loaded into a 'DELAY' subr.

I hope you can follow this.?

Trevors · 22nd April 2008, 01:33 PM

Hi Eric,
I understand what you've done. I need to get a little more familiar with the 628 though.

Txs again for your feedback / advice

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
PIC question from a PIC Virgin	bigal_scorpio	General Electronics Chat	9	21st March 2008 05:45 PM
Atmel, assembly:displaying on lcd	Haidy	Micro Controllers	13	11th February 2008 09:13 PM
Motor Controllers and serial comm?	RedCore	Micro Controllers	18	3rd July 2007 02:27 AM
Delay routine not working	gregmcc	Micro Controllers	6	18th September 2005 06:23 PM
Effects	stephenpic	Micro Controllers	6	19th January 2004 12:57 PM

21st April 2008, 06:25 PM	#3
Trevors	Txs Eric, Will take a look at it. __________________ "Better to have tried and failed, than to have failed to try"

21st April 2008, 07:06 PM	#4
ericgibbs	hi trevor, Just a thought, did you delete the delays you had in the 4514 mux, when driving the LED's??? If you have a spare analog pin, its easy to connect a pot and control the stepper rate by using the pot. __________________ Eric " Good enough is Perfect " I will NOT answer PM's requesting technical help, please use the Forum PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

22nd April 2008, 12:48 PM	#6
Trevors	Hi Eric, Yes, I still have the same delays. Don't have any analog pins though. Using a 16F84a, but I have purchased a 16F628a. Going to start using that soon. How would I implement the pot idea? Txs for those delays Donniedj. I'm sure those will come in handy. __________________ "Better to have tried and failed, than to have failed to try"

22nd April 2008, 01:33 PM	#8
Trevors	Hi Eric, I understand what you've done. I need to get a little more familiar with the 628 though. Txs again for your feedback / advice __________________ "Better to have tried and failed, than to have failed to try"