Re: [CAD_CAM_EDM_DRO] Re: Pixie error connection

Hello Keith,

The open collector transistor acts like a simple switch. It can be a
very low resistance to ground or it can be a very high resistance to
ground.

You don't need a pull up resistor here. If it is built in then just
ignore it.

Use the relay control inputs instead of, or in parallel with, the pull
up resistor. A pull up resistor is usually in the 1k to 10K ohm range
and can be ignored or not used.

The positive relay control goes to +5v. That is the same +5v where the
pull up resistor is, or would be, connected.

The negative relay control goes to the open collector. That is the same
place where the negative end of the pullup resistor is, or would be,
connected.

If this does not work then try to find out more about the open collector
current sinking capability (usually more than 2ma and sometimes as much
as 30ma) and the solid state relay control current requirement (might be
as high as 100ma or as low as a few microamps).

Tom Hubin
thubin@...

****************

toolspindoctor wrote:

>
> Tom,
>
> Connecting like that might make a big difference. Do I take the +
> side on the relay to the open collector and the neg side to +5v? Is
> any +5 ok to use?
>
> thanks
> Keith
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Tom Hubin <thubin@...> wrote:
> >
> > Hello Mark,
> >
> > Open collector outputs will sometimes drive a relay. One end of the
> > relay coil goes to the open collector output and the other end of
> the
> > coil goes to +5v...not to ground. The open collector can sink
> current
> > but sources nothing. The pullup resistor, if it is there, is the
> source
> > for +5v and that is rarely enough to drive a relay coil, although
> may be
> > enough to drive a solid state relay.
> >
> > Try to find out what the open collector device is and the max
> current
> > that it can sink when the output is low. Then use a relay coil or
> solid
> > state relay that requires less than that. Just be sure that the
> relay
> > input that is not tied to the open collector is tied to +5v.
> >
> > Sometimes you can tie it to +12v instead of +5v but that requires
> more
> > info to decide.
> >
> > Tom Hubin
> > thubin@...
> >
> > **************************
> >
> > toolspindoctor wrote:
> > >
> > > Mark,
> > >
> > > I appreciate your input! I had envisioned the Pixie error circuit
> as
> > > you described. I still don't understand why the error output would
> not
> > > be sufficient to drive a DC solid state relay. When I connect the
> > > error to the relay is just goes into an error state. There must be
> > > something different about the open collector, which I don't
> > > understand. Jim Cullins, who designed my breakout board has
> suggested
> > > interfacing with an IC with Darlington arrays.
> > >
> > > I have all the safeguards with limit switches etc. The system
> shuts
> > > down everything during an estop coming from my servo amps or from
> > > Mach3, the estop switch etc. However, the final protection is to
> get
> > > the servo amps to shut off (signal the Mach3-Campbell estop)when
> the
> > > Pixies fail. Now of course, the Pixies go into an error condition
> > > without triggering an estop.
> > >
> > > Thanks again,
> > > Keith
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mark Vaughan" <mark@>
> > > wrote:
> > > >
> > > > The pixie error output is am open collector output, and an input
> > > with pull
> > > > up resistors. What this means is each pixie card has a little
> > > transistor
> > > > switch that switches the line to 0V when there is an error. When
> > > there isn't
> > > > an error the pull up resistor keeps the output at 5V, but being
> a
> > > resistor
> > > > it is low current. The idea is that you can wire all the pixie
> card
> > > error
> > > > wires together so which ever one faults pulls the line of all
> the
> > > others to
> > > > 0V which the others see as an input and stop themselves so when
> it
> > > goes
> > > > wrong all pixie cards will stop so there will be no axis
> movement.
> > > >
> > > > As to interfacing to other systems, the output can only drive 5V
> > > logic,
> > >
> > >
> >
>
>