Re: [CAD_CAM_EDM_DRO] Re: Pixie error connection

Hello Keith,

> 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.

The TIP 3055 is a power transistor. Lots of current and power
capability, which you may not need. It won't do any harm but if it does
not work it will be because of low gain. You may need a higher gain and
not need so much current. So 2N2222 might be a better choice.

In any case, I would put the relay between the NPN emitter and ground so
as not to drain the 1ma from the 5K pullup.

Hmmm, now that I have said that, I am leaning toward agreeing with the
Darlington proponents. The impedance seen by the 5kohm source is the NPN
gain times the resistance between emitter and ground. So a very high
gain is desirable along with the load being between NPN emitter and
Pixie ground and not between Pixie +5vdc and NPN collector.

If you do use a Darlington NPN you don't need any pullup resistor
because the 5kohm pullup on the Pixie is sufficient.

If you don't have an NPN Darlington handy then you could use a 2N2222
and a TIP3055 together to make your own Darlington NPN pair.

BTW, have you verified that the relay works at all? Can you connect the
controls to +5vdc and ground and see that it activates?

Tom Hubin
thubin@...