Re: Encoder circuits for parallel port hookup?

I read one post were someone said he solved the problem with
something like a 15uf cap on the encoder power terminals. The cap
had to be on the encoder end. If you try this i would also put
a .1uf cap across it to....caps and resistors for the signal end
would have to be chosen carefully. They will tend to round off the
square wave edges. If you have to go this route maybe 100 ohm
and .01uf, from each signal line to gnd. Could also try toroids on
power and signal lines.

Of course there is a radical soultion, fix the problem!!! trying to
filter out the noise is like sticking a bucket under a leak to fix
it. Try the following.

1) Use shielded cable. The shield should only be connected to the
computer end, i usally solder it to the DB25 outer metal D ring.

2) Physically move the encoder cable away from power wires,
especially the motor wiring.

3) You said you used gearing, gearing is mechanical and usally
involves backlash. Dit you look there for problems.

4) well, how cheap are these encoders. It is possible you are
turning them faster than they can respond. By any miracle do you
have a scope...


Wally

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "AbbyKatt" <cnc@a...> wrote:
> Thanks for the response Art!
>
> Hmmm.. I ended up getting some pretty cheap mechanical encoders,
and
> just used some gearing to increase the res... But I seem to be
getting a
> problem with this. I'm guessing there may be some bouncing of the
> signal? I'm using Mach2 (will use Mach3, so I can do both X/Y
soon)..
> Sometimes it seems like the program will detect 2-hops instead of
one,
> and sometimes it'll switch out of the MPG mode (I'm guessing this is
> debounce and that Mach2 is detecting an invalid Quadrature sequence
and
> wisely bailing out of the mode?)
>
> Can I use some little capacitors with resistors across them or such
to
> filter this?
>
> Thanks
> Abby
>
>
>
> > -----Original Message-----
> > From: art [mailto:fenerty@a...]
> > Sent: 23 February 2005 13:44
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > Subject: Re: [CAD_CAM_EDM_DRO] Re: Encoder circuits for
> > parallel port hookup?
> >
> >
> >
> > Hi:
> > >>>> What I am looking for is the circuit diagrams that show
> > how to hook
> > > up
> > >> an optical encoder to the parallel port (I a
> >
> > No signal filters are usually necessary, you hook the A and
> > B quadrature
> > up to the pins on
> > the printer port directly, and you have to hook the signal
> > gound to pin 25.
> > Thats it. Mach3 can read
> > up to 7 of these if you have enough pins, but when reading
> > from a printer
> > port, your limited to the nyquist
> > frequency of the program reading it in terms of speed. In
> > Mach3's case, at
> > 25Khz mode, you are limited to
> > about 12500 pulses per second on the encoder, howver, Windows
> > being Windows,
> > I recommend a 10000
> > pulse limit and 20000 in 45Khz mode.
> >
> > I have seen some DOS software that wil read faster
> > though, and it is
> > possible for a Windows DRO program to
> > do up to 50000 per seconjd from an encoder if it doesn't have
> > to do motor
> > movements and such to limit
> > the interrupt time. I have letters from several that have
> > encoders hooked
> > up as semi-closed loop correctors
> > and they seem to work well within those limits. Personally, I
> > haven't had
> > time to hook up my linear scales to Windows yet,
> > but intend to do so next month to put closed loop corrections
> > into the code
> > base for Mach3 anyway..
> >
> > Marris has a post recently on the gecko group about hooking
> > an encoder
> > directly to a motor to make it follow the encoder
> > with very simple circuitry as well...
> >
> > Thanks,
> > Art
> > www.artofcnc.ca
> > ----- Original Message -----
> >
> >
> >
> >
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