Re: [CAD_CAM_EDM_DRO] Has anyone ever had trouble driving a G201 w/ an unbuffered parallel port?

Steven,

When I first started using the Gecko 201 I connected them directly to the
parallel port and got my 5 volts from the PC.

In the breakout board that Jim Cullins (Sound Logic) designed we use a
buffer so that our users can use any of the new PC parallel ports that only
output 3.5 volts.
We do not use opto-isolators for our step and direction lines. The
opto-isolators are in the Gecko drives.

We do use opto-isolators for the limit sensors as they provide a very good
filter for the transit noise pulses that cause problems with false triggers.

I hope that some of this will help.

We do not use an
Bob Campbell
Bob@...
www.campbelldesigns.com
Breakout board
THC board sets
CNC router plans
Stepper Motors

----- Original Message -----
From: "sciciora" <sciciora@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, May 09, 2004 2:17 PM
Subject: [CAD_CAM_EDM_DRO] Has anyone ever had trouble driving a G201 w/ an
unbuffered parallel port?


> Hello!
> Has anyone ever had trouble driving the G201's opto inputs with an
> unbuffered parallel port? the minimum input current requirements of
> the gecko is 16mA, and from p.108 of Jan Axelson's "Parallel Port
> Complete" it says printer ports can sink 12ma when the outputs are
> 0.4V (logic low). It also says that printer ports have an output
> impedance of 45 to 55 ohms. On the few printer ports I've tried,
> it's always worked, but I'm concerned that it is 'out of spec'.
>
> I have no problem adding a 74ACT245 buffer to drive the LEDs, but
> I'm afraid that this will un-do the majority of noise immunity that
> the opto-isolators provide. It's my understanding that optos work on
> current, not voltage. And that most noise sources are high
> impedance; too high to change the state of an opto. But the inputs
> of logic gates are high impedance and operate on voltage (not
> current). So a high impedance will have no problem changing the
> state of an input of a logic gate.
>
> If I buffer the printer port, should i low-pass filter the lines
> and then square them up with a schemidt trigger? This won't prevent
> noise like optos will, but will filter out spikes shorter than a
> certian amount.
>
> What do 'commercial' break-out boards do? Do they buffer, and
> noise filter at all?
>
> Has anyone tried any of the line termination techniques like what
> is shown on page 112 of the "Parallel Port Complete"? One of them
> shows each line on the reciving end with a 100 ohm resistor in series
> with a 100 pF cap, with the other end of the cap to ground.
>
> Sorry for all the questions, but I've been plagued by noise before,
> and want to make this box 'bullet proof'.
>
> Thanks!!
>
> - Ciciora
>
> P.S. As they say, in Engineering, there are no answers, only
> compromises. The 'best' answer is the one that minimizes the
> compromises.
>
>
>
>
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