I would first look at using an inexpensive PIC with a high clock speed ( li=
ke 64MHz) and just poll regular GPIOs and a single timer interrupt -- evalu=
ate if that's fast enough for the application. You can debounce  in firmwar=
e and save at least a dozen components. 10K and 10nF have a tau of 100us, s=
o if those values are realistic, polling at 10 kHz or 20 kHz might be fast =
enough. If they are mechanical encoders that is more than fast enough...the=
re is a limit to the count period set by the bounce time.

I don't see how you can connect all A's to a single INT pin-- unless you ex=
clusive OR'd each together, but that would require several gate chips and c=
ould be pattern sensitive in terms of missing steps. Maybe it's a true 3D '=
 mouse' or a Stewart platform-- 6 DOF would be required for that. If the la=
tter, the consequences of missing steps might be more serious. You might wa=
nt to determine that, and whether multiple encoders will be moving at once.

 Best regards,
--sp


> On Dec 23, 2013, at 5:02 AM, CDB <colin@btech-online.co.uk> wrote:
>=20
> I've been asked if I can conjure up  a device that will allow 6 increment=
al=20
> rotary encoders and 10 ADC inputs. I suspect this is for some sort of=20
> gaming doodad.
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> I'm wondering on what the lists thoughts are on saving 12 port pins with=
=20
> the following.
>=20
> Attach channel A of all the encoders to a single interrupt on change pin.=
=20
> The IOC will look for high to low and then low to high.
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> Attach all the B channels to individual pins on a port.
>=20
> On interrupt the complete port with 6 channel B's will be read in and=20
> masked in a sequential series to see which pin changed and the state it=20
> changed to - Xoring with a previous state buffer to get direction and=20
> count.
>=20
> Does this seem feasible and have I overlooked any pitfalls, other than=20
> possibly more than one encoder being twiddled at the same time?
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> I would debounce in hardware with probably a 10K pullup and 10nF capacito=
r=20
> per input.  Pushbuttons on the encoders are not required, but the pins us=
ed=20
> by an encoder could be substituted with push buttons,  I was thinking of=
=20
> having a Pic pin that could be set high or low to signal whether push=20
> buttons or encoders were attached.
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> It wouldn't surprise me if there wasn't a future requirement for the last=
=20
> option to be set via a PC to the Pic.
>=20
> Colin
> --
> cdb,  on 23/12/2013
>=20
>=20
>=20
>=20
>=20
>=20
> --=20
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> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

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