Rotory encoder

Gerrit · Joined: 15 Sep 2003 Posts: 58

Hello,

I am using an alpha low-ocst rotory encoder.

At this moment I have extra pulses when I just turn the
knop to and from the detent point.

Is there a way to avoid fals pulses?

I have added some code whitch will be called from insite the timer_1

Regards,

Gerrit

Steph · Joined: 06 Dec 2003 Posts: 3

Hi gerrit

In my case, i am using a IC from US Digital:
LS7083; encoder to counter interface.
I am using an optical encoder.

If you are using a mechanical encoder,
you will need to debounce with a time delay.

Some examples:
if you look on CCS examples folder
look for: EX_ENCODE.C

i found that one on internet too:

PIC Micro Controller C Input / Output Routine
Quadrature Encoder ISR
by David Kott

struct RotaryEncoderStruct {
int unused:4; // RB[0:3]
int A:1; // RB4
int B:1; // RB5
int unused2:2; // RB6-7
};

struct RotaryEncoderStruct RotaryEncoder;

#pragma BYTE PORTB = 0x06

#pragma BYTE RotaryEncoder = 0x06 // Place structure right over PORTB at
location 0x06

USHORT g_usEncoderCount = 0;

#pragma INT_RB
void
PortBInterrupt (void)
{

static BYTE OldPortB;
BYTE byTemp;
static struct RotaryEncoderStruct OldEncoder;

if (OldPortB != (byTemp=(PORTB & 0x30))) {

OldPortB = byTemp;

if (RotaryEncoder.A == OldEncoder.A) {
if (RotaryEncoder.B == RotaryEncoder.A)
--g_usEncoderCount;
else
++g_usEncoderCount;
} else {
OldEncoder.A = RotaryEncoder.A;
if (RotaryEncoder.B == RotaryEncoder.A)
++g_usEncoderCount;
else
--g_usEncoderCount;
}
}
}

Good luck

Ttelmah · Guest

Gerrit · Joined: 15 Sep 2003 Posts: 58

Hi Ttelmah,

I print it out and start reading today, tomorrow I wil try this
to see if this is more conviniend.

Thanks Steph and Ttelmah you for you response.

Kind regards,

Gerrit Faas

valemike · Guest

Hi,
This has been addressed in the comp.arch.embedded newsgroup

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=1079035907snz%40amleth.demon.co.uk&rnum=14&prev=/groups%3Fq%3Dvalemike%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26scoring%3Dd%26start%3D10%26sa%3DN

I had that same problem once before. Bottom line is - these mechanical rotary switches are good to find the position of the switch, but not for counting. For example, going from position 1 to position 2 will look like:
0001 -> 0000 (intermediate) -> 0010.
These contacts break intermediately before the others make. A worse scenario is going from 7 to 8:
0111 -> 0011 -> 0001 -> 1000 -> 1000 (something like that. basically, you can have up 3 intermediate states).

All the debouncing in the world won't help you if the person has a very steady hand and wants to fool it. You'll need a few hundred milliseconds of delay to get to detent position, but even that's not guaranteed against a slow and steady hand. Trying doing printf() to Hyperterminal and dump the values you see. You'll find that when you go backwards, it is more "predictable". For example, if you're at position 8 (1000), and you go backwards, you'll probably see an intermediate value of 0 (0000) before the 0111 (7) eventually gets detented. So when you see an intermediate 0, you can "predict" that the guy is going backwards to 7, and don't have to worry about further intermediate positions.

Mike