Re: [CAD_CAM_EDM_DRO] Re: Pixie error connection

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,
>
>