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a code for the shaft encoder

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nicholastyc

Mon Jun 16 2008, 03:33AM

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Hi,

I have problem writing a code for the shaft encoder to decode for my PIC to read the direction.
Can some one please give me a sample code of the shaft encoder decodes the direction?

thanks.

nicholastyc

Mon Jun 16 2008, 03:51AM

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Ajay, i know you already told me about this...but i try to work it out on ASM code...it doesnot work..

can u give me a sample code of how to decode the shaft encoder direction?

nicholastyc

Mon Jun 16 2008, 04:14AM

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GPIO 4 is the channel A of the shaft encoder
GPIO 5 is the channel B of the shaft encoder
below is part of the program code for the encoder to decode the 4 binary bit to determine the direction.
shaft encoder used Bourns ECW- Digital Contacting Encoder

CODE:

START

        btfsc   GPIO,4;    waiting for the encoder changes

        goto START; keep check for the changes

        call    SHAFT_0; changes detected

SHAFT_0:

        CLRF    A11             ; clear memory A11

        CLRF    A21             ; clear memory A21

        BCF     STATUS,C; clear carry flag incase there is carry

        BTFSC   GPIO,4          ; check on the changes, 0 or 1

        GOTO    SAVEBIT_A11     ; if 1 go savebitA11

        GOTO    SAVEBIT_A10     ;if 0 go savebit A10

SHAFT_1

        BTFSC   GPIO,5          ; check on gpio 5 changes, channel B

        GOTO    SAVEBIT_B11     ;if 1 go savebit B11

        GOTO    SAVEBIT_B10     ;if 0 go savebit B10

SHAFT_2

        BTFSC   GPIO,4          ;same as above to check to the 4th bit

        GOTO    SAVEBIT_A21     ;

        GOTO    SAVEBIT_A20     ;

SHAFT_3

        BTFSC   GPIO,5          ;

        GOTO    SAVEBIT_B21     ;

        GOTO    SAVEBIT_B20     ;

SAVEBIT_A11

        MOVLW   b'00000001'     ; if 1 received on shaft channel A move 1 to A11 memory

        MOVWF   A11             ;

        RLF     A11,1           ; rotate left to make bit 0 avaible for channel B

        GOTO    SHAFT_1         ;

SAVEBIT_A10

        MOVLW   b'00000000'     ;if 0 received on shaft channel A move 1 to A11 memory

        MOVWF   A11             ;

        RLF     A11,1           ;rotate left to make bit 0 avaible for channel B

        GOTO    SHAFT_1         ;

SAVEBIT_B11

        MOVLW   b'00000001'     ; if 1 received on shaft channel B move 1 to A11 memory

        IORWF   A11,1           ;added up with channel B to form 1 complete bit for 

        RLF     A11,1           ;each turn, rotate left 2 times for next bit of turn 

        RLF A11,1       ;                                            of the encoder

        GOTO    SHAFT_2         ;

SAVEBIT_B10

        MOVLW   b'00000000'     ; same as above ...for 0 bit on channel B

        IORWF   A11,1           ;

        RLF     A11,1   ;

        RLF A11,1

        GOTO    SHAFT_2         ;

SAVEBIT_A21

        MOVLW   b'00000001'     ;if 1 received on shaft channel A move 1 to A21 memory

        MOVWF   A21             ;

        RLF     A21,1           ;rotate left to make bit 0 avaible for channel B

        GOTO    SHAFT_3         ;

SAVEBIT_A20

        MOVLW   b'00000000'     ;

        MOVWF   A21             ;same as above

        RLF     A21,1           ;

        GOTO    SHAFT_3         ;

SAVEBIT_B21

        MOVLW   b'00000001'     ;bit 1 , added up with channel A to form 1 complete bit for

        IORWF   A21,0           ;each turn

        IORWF   A11,0           ;at here, add up 2 complete bit to determine the 

        GOTO    DIRECTION       ; direction of the shaft encoder...

SAVEBIT_B20

        MOVLW   b'00000000'     ;same as above, but 0 bit received from previous action

        IORWF   A21,0           ;

        IORWF   A11,0           ;

        GOTO    DIRECTION       ;

DIRECTION

        CALL    TABLE_1 ; call table to check on the direction after the total 4bit added

ANTI_CLOCKWISE

        BSF     GPIO, 0; set gpio 0 high

                     BCF               GPIO,1; clear gpio 1

        goto    START;

CLOCKWISE

        BSF     GPIO,1;set gpio 1 high

        BCF     GPIO,0;clear gpio 0

        GOTO    START;

RESTART_PWM

        GOTO    START; no changes go back to start

        RETURN

;************************************************

;**** DIRECTION TABLE****************************

;************************************************

TABLE_1:

        ADDWF   PCL,1   ;

        GOTO    RESTART_PWM     ;

        GOTO    ANTI_CLOCKWISE  ;

        GOTO    CLOCKWISE       ;

        GOTO    RESTART_PWM     ;

        GOTO    CLOCKWISE       ;

        GOTO    RESTART_PWM     ;

        GOTO    RESTART_PWM     ;

        GOTO    ANTI_CLOCKWISE  ;

        GOTO    ANTI_CLOCKWISE  ;

        GOTO    RESTART_PWM     ;

        GOTO    RESTART_PWM     ;

        GOTO    CLOCKWISE       ;

        GOTO    RESTART_PWM     ;

        GOTO    CLOCKWISE       ;

        GOTO    ANTI_CLOCKWISE  ;

        GOTO    RESTART_PWM     ;

        RETURN

Ajay

Mon Jun 16 2008, 07:45AM

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Welcome back nich well in your program you have used so many returns.. i really have no idea where you're returning

Well minute changes will make your program work..
like..

CODE:

START

        btfsc   GPIO,4;    waiting for the encoder changes

        goto START; keep check for the changes

        ;call   SHAFT_0; changes detected

        ;No need to call the next statement is same you are going to execute

I found that there is no while(1) kind of loop in your program.

please tell me what your application is or what you are trying to do in your program, so that i can optimize it better. and please review your code and remove the unwanted returns, because they will make your program to go mad and hang!!

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nicholastyc

Mon Jun 16 2008, 08:17AM

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hihi, ajay,
my application is for the LED dimmer, i need to know when i am turning clockwise or anti clockwise of the encoder, the light is either dimmer or brighter.

i want to know the changes of direction, so i can set the PWM.

Thanks

Ajay, the main problem i m having now is, how to detect the changes of the encoder signal bits, and how to save them efficiently and bring them to determine the direction using IOR table i am using.
thanks...

[ Edited Mon Jun 16 2008, 08:39AM ]

shyam

Tue Jun 17 2008, 06:23AM

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hi
nicholastyc
if u had searched the forum u wud have found an earlier post on the similar topic.
still lemme tell u one technique which i use..

u get two o/p lines
say A and B
u get data in gray code format (cyclic).

thhere will be two sets of data
1. clockwise (depends on what pin A or B is)
A|B
0|0
0|1
1|1
1|0
and
2. anticlockwise
A|B
0|0
1|0
1|1
0|1

now u wud have observed the difference just compare any two occurance of data and u will find the direction...
hope that helps...

lProgress is not made by early risers or hard workers, but by LAZY people, trying to find easier ways to do the same........

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nicholastyc

Ajay

Tue Jun 17 2008, 07:41AM

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like you have done in C already, here also you need to make a look up table for encoder to detect the change in direction.

or... what you can do is.. create three states (CLOCK, ANTICLOCK, NOCHANGE)
like this:

CODE:

CLOCK equ 1H

ANTICLOCK equ 2H

NOCHANGE equ 3H

if encoder can be connected to interrupt pins of controller or periodic polling on any two pins, then whenever you sense a change in encoder o/p you can switch between states according to current state of encoder bits.
hence in your main loop when a state changes you can do work according to that state.

I hope you have got my idea?

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nicholastyc

nicholastyc

Wed Jun 18 2008, 01:11AM

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I was using both of your idea in my design, i make it working on hardware now...but littlt buggy is that...when u over turned the shaft encoder, the light from the dimmest will changed to Brightest ...lol...
little buggy with my code here...need to prevent it to overshoot....

thanks anyway...i will figure it out...

nicholastyc

Thu Jun 19 2008, 09:02AM

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Joined: Wed May 07 2008, 07:13PM

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CODE:

for example:

START

        btfss             GPIO,4; check encoder changes

                     goto       START

        clrf    SWDAT2; clear reg

                     btfss   GPIO,4             ; if bit A lo

                     bsf     SWDAT2,0         ; set SWDAT2 bit 0

                     btfss   GPIO,5  ; if bit B lo

                     bsf     SWDAT2,1         ; set SWDAT2 bit 1

        movf    SWDAT2,W        ; load switch data                |B0

        andlw   b'00000011'     ; mask encoder B and A switches   |B0

        xorwf   ENCOLD,W        ; same as last reading?           |B0

        bz      START     ; yes, branch (no change), else   |B0

        xorwf   ENCOLD,W        ; restore encoder bits in W       |B0

        rrf     ENCOLD,f        ; prep for B-old ^ A-new          |B0

        xorwf   ENCOLD,f        ; ENCOLD bit 0 = direction        |B0

        rrf     ENCOLD,f        ; now Carry bit = direction       |B0

        movwf   ENCOLD          ; update ENCOLD (new BA bits)     |B0

        btfss   STATUS,C;

        goto    ANTI_CLOCKWISE;

        goto    CLOCKWISE;

i m using pic12f629...
can some one suggest me a WORKED code?

[ Edited Thu Jun 19 2008, 09:05AM ]

nicholastyc

Thu Jun 19 2008, 02:59PM

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Shyam , Ajay...Arun...

i really need help on the encoder part...please help..i already tried my best !
i still cant get the right direction ... i m using pic12f629 ...
i am using Gpio,4 and gpio,5 as Bit A and Bit B of encoder.
1. clockwise
A|B
0|0
0|1
1|1
1|0
and
2. anticlockwise
A|B
0|0
1|0
1|1
0|1

how to make a correct table? i m trying to make 1...its works on the simulation but failed on hardware...dunno y...
do i need the interrupt routine? because i m using the btfss gpio,4 to enter the direction loop and then check on the bit on A and B. same as the code in the thread above...

pplease have a look...or give me a code to try...i m so so so depressed!

thanks