On Mon, Jun 10, 2013 at 6:38 AM, Denny Esterline <desterline@gmail.com> wro=
te:
> "Best" is a matter of opinion and what you're trying to achieve. Easiest =
is
> usually to only use one of the interrupts and either increment or decreme=
nt
> based on the state of the non-interrupt pin. (interrupt when A channel go=
es
> high and increment if B is high, decrement if B is low)
> Personally I'm fond of a different technique which results in higher
> resolution. But it does require storing the previous state of the encoder
> and interrupting on both rising and falling edges of both A and B channel=
s.
> After an interrupt, XOR previous B value with the current A value.
> Increment or decrement based on the result. Don't forget to save the valu=
e
> for the next interrupt.
>
> A third technique is to concatenate the encoder bits and use it as the
> index into a lookup table. Where the results of the lookup are +1, -1 or =
0
> that are then added to your counter variable.

I freed up some associated pins on the microcontroller.

http://farm4.staticflickr.com/3763/9005870401_b52fc6b8fd_o.jpg

Using PORTB change interrupt to detect the Encoder event,

RB4 connected to Encoder B
RB5 connected to Encoder A

RB6, RB7 connected to ICSP
You can see the OLED displaying the count in the picture.


http://hifiduino.wordpress.com/2010/10/20/rotaryencoder-hw-sw-no-debounce/

Bourns has an application note on debouncing:
http://www.bourns.com/data/global/pdfs/Bourns_enc_sgnl_cond_technote.pdf

Seemed like the lookup way was quite reliable and fast too, hence.

One thing that I don't understand is, why he does this:

" static uint8_t old_AB =3D 0;"

that would loose the previous state altogether, wouldn't it ?

So, I put up some code which does the following on a PIC18F4550


const s8 rom enc_states[] =3D { 0,-1,1,0,1,0,0,-1,-1,0,0,1,0,1,-1,0 };
u8 c_state =3D 0;

#pragma interrupt hi_interrupt
void hi_interrupt(void)
{
	if (INTCONbits.RBIF) {
		INTCONbits.RBIF =3D 0;
		LATD =3D disp_bits[1];
		LATE =3D 1;                                   /* on display:1 */
//		c_state =3D 0;
		c_state <<=3D 2;                            /* previous state */
		c_state |=3D (PORTB >> 4) & 0x03; /* add current state */
		count +=3D enc_states[(c_state & 0x0f)];
	}
}

and I am simply displaying the count:

buf[0] =3D count;
ssd1308_wr_str(buf, 8);

Running it, the count doesn't seem to be correct, sometimes jumps by
increment of 4 sometimes 1 etc.

Any other thoughts how to better debounce the input ? Or is it a bug,
rather than a debounce issue ?

Thanks,

Manu
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