You only need two input lines. Here's a bit of documentation from a project I did once:
;--------System design notes-------------------------------------
;
; The encoders output a 2-bit value:
; the A-bit signals rotation,
; the B-bit signals the direction of rotation.
; encoder movement is detected by polling and debouncing in the b-port.
;
;CW channel A ___ ___ ___ [channel A leads channel B]
; ___| |___| |___|
;
; channel B ___ ___ ___
; |___| |___| |___|
;
;
;
; CCW: channel A ___ ___ ___ [channel A trails channel B]
; ___| |___| |___|
;
; channel B ___ ___ ___
; __| |___| |___|
;
; A-bit B-bit Direction
; 0>1 0 CW
; 1 CCW
; 1>0 0 CCW
; 1 CW
You poll the A-bit (or hang it on an interrupt line) and then check the B-bit for direction of rotation. Ther's probably a ton of other ways to do this, this happened to work for me.
Edit: I realize the formatting is screwed up, if needed I can email it to you.
Jan Didden
;--------System design notes-------------------------------------
;
; The encoders output a 2-bit value:
; the A-bit signals rotation,
; the B-bit signals the direction of rotation.
; encoder movement is detected by polling and debouncing in the b-port.
;
;CW channel A ___ ___ ___ [channel A leads channel B]
; ___| |___| |___|
;
; channel B ___ ___ ___
; |___| |___| |___|
;
;
;
; CCW: channel A ___ ___ ___ [channel A trails channel B]
; ___| |___| |___|
;
; channel B ___ ___ ___
; __| |___| |___|
;
; A-bit B-bit Direction
; 0>1 0 CW
; 1 CCW
; 1>0 0 CCW
; 1 CW
You poll the A-bit (or hang it on an interrupt line) and then check the B-bit for direction of rotation. Ther's probably a ton of other ways to do this, this happened to work for me.
Edit: I realize the formatting is screwed up, if needed I can email it to you.
Jan Didden
I had try to write some,but it has dithering,so it is not steady
Could you send me the program you had write for MCS51 , I want
to have a reference.
my mail box is cacworld@126.com
Could you send me the program you had write for MCS51 , I want
to have a reference.
my mail box is cacworld@126.com
You have to debounce the bits. At the moment the switches close/open they bang around some time, depending on the quality of the encoder, but they all do it. So once you detect bit change, you wait a couple of milliseconds (I forgot exactly how many, it's trial and error and depends as I said on the type/brand of encoder), then after the delay you check the bit values and do your processing.
Edit: I think I used 6 msec debounce. Can't take too long, else you miss some pulses if someone turns it real fast...
Jan Didden
Edit: I think I used 6 msec debounce. Can't take too long, else you miss some pulses if someone turns it real fast...
Jan Didden
cac liu said:
I'm sorry but there is no 'program' to speak of...
It depends on the microcontroller you use, in 'meta-speak', you can do (with polling):
- see if the A bit is different from last time you looked;
- if yes, wait the debounce period;
- test the A-bit status (one or zero);
- test the B-bit status;
-depending on one of the four combinations, go to a routine to do whatever you want to do as action to the encoder movement.
I did this in a PIC and it is just a bunch of bittest and goto statements, but embedded in the program so I can't really send it to you.
But if you understand the process it should be a no-brainer.
Jan Didden
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