On 12/23/2013 11:57 AM, Dwayne Reid wrote:
> Comments in-line.
>
> At 03:02 AM 12/23/2013, CDB wrote:
>> I've been asked if I can conjure up  a device that will allow 6 incremen=
tal
>> rotary encoders and 10 ADC inputs. I suspect this is for some sort of
>> gaming doodad.
>>
>> I'm wondering on what the lists thoughts are on saving 12 port pins with
>> the following.
>>
>> Attach channel A of all the encoders to a single interrupt on change pin=
..
>> The IOC will look for high to low and then low to high.
> This won't work.  Assume that the encoders are open-collector (or
> mechanical switches) that go to Ground when closed.
>
> When any one encoder is in a position that channel A is grounded,
> none of the other encoders can change that pin.  You will see changes
> on the individual channel B lines, but without seeing the changes on
> the channel A line, you can't tell direction.
>
> Also note that the method you are proposing, which is treat channel A
> as the clock line and channel B as the direction line; can suffer
> from false counts because of jitter on the channel A line.  That is:
> assume that the encoder is right at the transition point for channel
> A.  You get clock edges but no direction changes.  This results in
> false counts.
>
> Been there, done that, learned NOT to do it that way <grin>.
>
> There are a couple of ways to do this.  But, honestly, I'd dedicate
> either a small PIC (with enough pins for all 12 encoder lines) and
> poll the pins at a very fast rate.  Then use the standard 4-entry
> lookup table for each of the encoders or, if you are feeling
> ambitious, the also-standard 4-state state machine for each of the encode=
rs.
>
> dwayne
>
I'm using a seperate PIC16F1933 as a quad decoder for 4 channels of=20
motors. Firmware de-bouncing is very reliable, with a huge memory for=20
keeping track of the count. During non-motor movement times, the PIC=20
handles RS232 access to a small notebook PC to help us to setup our=20
solar installations. The various counts are stored in EEPROM in=20
triplicate to be sure that the count is always accurate, even during=20
power off situations.

The PIC16F1933 officially can be run at 32Mhz but I can run it easily at=20
40Mhz at 5V by using a 10M resonator instead of an 8M. Plenty fast for=20
anything we're doing.

These PIC's are cheap, too; about $2 USD. Special quad decoders cost $15=20
or more.

--Bob

--=20

The only place success comes before work is in the dictionary.

VINCE LOMBARDI

--=20
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