decoding quadrature encoders

[Luciano]

If you are losing encoder counts, then use an interrupt service routine.
Four of PORTB’s pins, RB<7:4>, have an interrupt-onchange feature.
Use two of these pins for the A/B encoder signals.

Luciano

[ice]

ok,heres my program ,using interrupts..

the problems i'm encountering are below the code
..

DEFINE LOADER_USED 1


led     VAR     PORTB.7
old 			VAR BYTE
new 			VAR BYTE
direction_bit 	VAR BIT
counter 		VAR WORD
counter_1		VAR WORD
counter_2		VAR WORD
direction_store	VAR BIT
adval			VAR	WORD				' Create adval to store result
potval			VAR WORD
servo_val		VAR	WORD
difference		VAR WORD
	

counter=32500		
	
    	HPwm 0,150,20000    
        OPTION_REG = $7f        
        ON INTERRUPT GoTo myint     ' Define interrupt handler
        INTCON = $90                     ' Enable INTE interrupt

	

loop:   High led                ' Turn LED on

		LCDOut $fe,1,"count:"
		LCDOut $fe,$c0,DEC counter
		'Pause 10
		
        GoTo loop               ' Do it forever




		' Interrupt handler
        Disable                 ' No interrupts past this point
myint:  Low led                 ' If we get here, turn LED off
       
       
enc:    new= PORTB & %00000011


start_1:
		old=new & %00000011	
		
again:

		new= PORTB & %00000011					'load new value of A/B channels into new by anding with HEX3
			
		
	    'IF new=old Then again
	    direction_bit=old.bit1 ^ new.bit0		'check direction 
	
		
		IF direction_bit = 1 Then  
		LCDOut $fe,1,"Last was CW"
		counter = counter + 1				'increment counter
		LCDOut $fe,$c0,DEC counter," ",BIN direction_bit
	
		Else
			LCDOut $fe,1,"Last was CCW"
			counter = counter - 1				'decrement counter
			LCDOut $fe,$c0,DEC counter," ", BIN direction_bit	
		
		EndIF
		Pause 10
	   			

              
		INTCON.1 = 0           ' Clear interrupt flag
	    Resume                 ' Return to main program
	    Enable

1>The interrupts are worng fine,however the code is still unable to distinguish between CW and CCW,because of which the counting goes awry..

2>if i remove the "if then " statement for CW/CCW direction and only put a
counter=counter+1,it works well


The whole problem seems to be the direction decoding part..
..i cant seem to find a solution to it..

[Luciano]

Hi!

1.
You are using the wrong interrupt.
Four of PORTB’s pins, RB<7:4>, have an interrupt-onchange feature.
Use two of these pins for the A/B encoder signals.

2.
Use assembly code for the interrupt.
(See PicBasic Pro manual).

3.
In your code the variables "new" and "old" will have
most of the time the same values.

In your code you are doing that:

new= PORTB & %00000011 'get encoder A/B
old=new & %00000011 'old is now same as new
new= PORTB & %00000011 'get encoder A/B again

When you get A/B again, it is very likely that the encoder is
still in the same position, therefore the variables new and old
will have the same values.

* * * *

Did you try the code I posted the 12th April 2005, 11:00?
Does it work if you turn the encoder slowly?

Luciano

[ice]

Luciano,

when i try the program u recommended [12th april] as below,
there are alot of instances when the program gets confused with direction,
so it sometime increments and decrements.Im not using interrupts

when i move the motor slowly,the problem still persists.

old_val 		VAR BYTE
new_val 		VAR BYTE
direction_bit 	VAR BIT
enc_counter 	VAR WORD
adval			VAR	WORD				' Create adval to store result
potval			VAR WORD
servo_val		VAR	WORD
difference		VAR WORD
	
TRISB=%11111111
enc_counter=32500		
HPwm 0,100,20000	
    
	

	new_val = PORTB & %00000011
start:
	old_val = new_val
	
	
again:
	new_val = PORTB & %00000011
	'LCDOut $fe,1,"no move"
	IF new_val = old_val Then again

	direction_bit = old_val.bit0 ^ new_val.bit1
	
	IF direction_bit = 1 Then  
	
		LCDOut $fe,1,"Last was CW"
		enc_counter = enc_counter + 1
		LCDOut $fe,$c0,DEC enc_counter

	Else
		LCDOut $fe,1,"Last was CCW"
		enc_counter = enc_counter - 1
		LCDOut $fe,$c0,DEC enc_counter	
	
	EndIF
    	GoTo start

Thank you for your responses

[Luciano]

Hi!

I need more info.

The version of the PIC used. (16F628, 16F628A, ...).

If you are using a commercial board for the PIC, I need
the URL where I can see the board.

The brand and model number of the encoder and the URL where I can
download the data sheet.

I also need to know how you have connected the encoder to
PORTB.0 and PORTB.1. (Pull-up resistors? If yes, values).


Luciano

[ice]

Luciano,

The version of the PIC used. (16F628, 16F628A, ...).

im using the PIC16F873A

If you are using a commercial board for the PIC, I need
the URL where I can see the board.

I made my own dev board..has an LCD,A/D..the usual features..
works on a 4Mhz crystal..
The board works perfectly as i have run accelerometers,D/A converters from the same board

The brand and model number of the encoder and the URL where I can
download the data sheet.

Maxon 22578
500 counts per turn
http://www.maxonmotor.com/docsx/Down...f/05_238_e.pdf

I also need to know how you have connected the encoder to
PORTB.0 and PORTB.1. (Pull-up resistors? If yes, values).

Pull up resistors
with value 1.8K


Thanks for all your help

[ice]

ok,a little progress,
seems like i'm loosing counts ,because of the LCDout commands

if i make my code tighter[remove the LCDcommands],i am able to monitor direction ,but a bit of interference still persists.
I'm on a 4Mhz..i'll switch to a 20Mhz tomorrow and post my progress