Re: Pixie error connection

Tom,

I appreciate your suggestions and hope to give them a try tonight.
What do you think about the Radio Shack NPN transistor I listed below?
I am trying to connect the Pixie error signal to my estop switch. All
I need is to have a switch open when the Pixie error goes to 0v.

Thanks
Keith

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Tom Hubin <thubin@...> wrote:
>
> Hello Keith,
>
> I jumped into this thread well after it started so I am still playing
> catchup with the end goal.
>
> I don't know what you are controlling with the relay but, since you want
> to control it with the error signal, I presume that you want the relay
> to be as safe as if the control inputs got disconnected or the Pixie
> board lost power.
>
> In that case, you need for the relay to be active only when the open
> collector error signal is off or high. In that situation you only have
> 1ma source from the 5kohm pullup resistor tied to +5vdc.
>
> Solution number 1 is to find a solid state relay that can be activiated
> by as little as 1ma. You can test this with a 5kohm resistor in series
> with a +5vdc supply and the control inputs.
>
> Solution number 2 is to amplify the 1ma of available current from the
> 5kohm pullup resistor to whatever current the relay requires to
> activate. A 2N2222 NPN transistor, wired as an emitter follower, may be
> sufficient. The transistor has a gain of something like 60 so can, if
> necessary, source up to 60ma for the relay control input.
>
> To wire the NPN transistor as emitter follower:
> Connect the Pixie +5vdc to the NPN transistor collector.
> Connect the NPN transistor emitter to the relay control positive.
> Connect the relay control negative to the Pixie 0v or ground.
> Connect the NPN transistor base to the Pixie open collector ERROR.
>
> If you connect the relay control between +5vdc and the NPN collector,
> instead of between the NPN emitter and ground, the relay will also work.
> However, the low impedance with the NPN emitter connected directly to
> ground will likely be seen by the Pixie as an ERROR because the voltage
> at the open collector will now be very low.
>
> If the relay needs much more than 50ma at the control inputs then I
> would use a Darlington NPN instead of a 2N2222. I would still wire it as
> an emitter follower for the same reason given above.
>
> Tom Hubin
> thubin@...
>
> *******************
>
> toolspindoctor wrote:
> >
> > Mark,
> >
> > Radio Shack has TIP3055 NPN Transistor and some others as well. This
> > one has a power dissipation of 90W.
> >
> > * Mfr.#: TIP3055
> > * Case type: TO-220
> > * V(CE): 1.1
> > * V(BE): 1.8
> > * I(C) Max: 15.0A
> >
> > Would this fit the bill?
> >
> > Thanks
> > Keith
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mark Vaughan" <mark@>
> > wrote:
> > >
> > > Hi Keith
> > >
> > > Yes one of these will probably do the trick, though it seems
> > pointless to
> > > buy an array when you only have one relay to interface to.
> > >
> > > Most simple darlington or hi gain npn transistors should do the job,
> > hence I
> > > commonly use MPSA13's because I have bucket loads of them. You can
> > connect
> > > the base via a resistor to the pixie card, 10K resistor would
> > probably be OK
> >
> >
>