decoding quadrature encoders

[ice]

Thank you for all your help.
Theres a small problem though.

The encoder program counts faster in one direction and slower in the other...

is it because ...
When im counting in one of the directions ,im utilizing the ADC[ADCIN and an IF statement]

..whereas in the other direction,im not.
The program logic is the same as above.

[Luciano]

I don't understand.
If you need help post your code.

Luciano

[ice]

before i go ahead with my code....ill explain wht i have to do

I need to control the position of a DC motor[geared],using a potentiometer

I have to first detect the endpoints of a gear assembly.
say, i start with a count of 32500 and the count at one end of the gear assembly is 32600
..now i rotate it to the other side ,say the count at this point is 32400

The above was just the calibration routine.Using the above values ,i have to
scale the 200 counts[32600-32400] to a potentiometer value[0 to 255]

How am i detecting the end points?
..im using the LMD18200T motor driver .Using the current sense feature of the chip,i detect wheteher the gear assembly has reached an end point.The current sense pin is connected to an ADC port..portA.1 namely


my program flow...
1> set counter to 32500
2> move motor in one direction
3> count pulses..if CW,increment.if CCW decrement
...say it is CW and counter increments to 32600 till the end
4>counter_1 has 32600
5>move the motor to the other side,count the pulses..it is decrementing now
6>so counter_2 has 32400
7>now i have to scale the gear assembly range to a potentiometer
difference=counter_1-counter_2
=32600-32400
=200
8> scale to a pot value
pot_val holds the pot value connected to analog portA.0

hence required count value=[difference/256]*pot_val+counter_2
=[difference*pot_val]/256+counter_2 (rearranging)

example...if potvalue in 128,then
required count value=(200*128)/256+32400
=32500

now i dont know where to go from here..how do i get the motor to move to position 32500,when the pot is moved to 128

...this is a long post..but its the best i could do to explain wht im trying to do.
-Gerry

[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