I am also interested in this problem....although I have a slightly different
problem. I am a newbie to PICS, and I am attempting to design a PIC circut
for reading a shaft encoder attached to a motor, and that has a really fine
grain.  I don't have a data sheet on the encoder....but when hooked up to
the scope, I am getting a 28 microsecond pulse width, with the motor turning
at the highest RPM for my application.  If I don't want to miss any pulses,
I need to be sampling at a rate of about 36khz (36,000 pulses per second).
I have two motors I would like to monitor with one PIC.  What I would like
to do, is have the PIC pull in the shaft data, and keep track of it, and
then deliver it over a serial line when asked for the totals.  What would be
the best PIC for doing this?  I want to make sure my clocking is fast enough
that there is no chance of missing a pulse.

Thanks,

- Ted


-----Original Message-----
From: cdb [mailto:bodgy1@OPTUSNET.COM.AU]
Sent: Thursday, April 17, 2003 9:10 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]:Optical Encoder and PICs


On Thu, 17 Apr 2003 08:01:48 -0400, Mccauley, Daniel H wrote:
 was wondering if anyone had experience of using an optical encoder
(A and
B inputs for quadrature mode) on a PIC microcontroller.
I'd like to use the A and B output of the optical encoder and tied
into
PortB and have each pulse (either on A or B) trigger an interrupt.

I don't with an optical version, but here is some code in 'C' that
you can play around with. See also another incarnation elsewhere in
last weeks archives, where I had a counting problem with my original
 code.

//EncoderA_pin on PORTA: 1. B_pin on PORTA: 0
//This checks for the sequence 10->11 for CW pulses and 11->01 for
CCW.
void getenc()
{

        if (!bRA0)              //enc_B is low
                old_enc_state=1;        //make flag high

        //we get here if both enc_B is now high and      old assumed state
was
high
        if ((bRA0) && (old_enc_state))
                {
                        if (bRA1)               //If enc_A is now high we
have gone from 10->11 in
pulses
                                {
                                        enc_state=1;
                                        old_enc_state=0;        flag now low
so that we have to wait for the
next 11 to come around
                                }
                                if((!bRA1) && (old_enc_state))
                                        {
                                                enc_state=-1;
                                                old_enc_state=0;
                                        }

        }
else
        {
                enc_state=0; //here if there was no change in encoder
position
        }
}

Colin
--
cdb, bodgy1@optusnet.com.au on 18.04.2003

I have always been a few Dendrites short of an Axon and believe me it
shows.

Light travels faster than sound. That's why some people appear bright
until they speak!

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