Joe, In the words of Roseanne Rosannadanna, you ask a lot of questions! :-)
You don't wire the coils of relays in series for relay logic. The coil voltage is selected to match the voltage you want to use to activate it... 5VDC, 12VDC, 24VDC, 120VAC, etc. You wire the relay contacts in series to implement an AND function (as is the case with your E-stop switches and a relay that mirrors the status of the internal LinuxCNC E-stop signal, and any other relay controlled signal you want to generate an E-stop). You'd wire the contacts from different relays in parallel to implement an OR function. The reason I suggested using relay logic for this application is simplicity. You'll need a relay to externalize the internal E-stop status anyway, so just wire the contacts in series with any E-stop switches you have and you're finished. Why add any discrete logic ICs to that? It's needless complexity. I'm generally a big fan of implementing logic in software or firmware. I've replaced a lot of goofy 1950s technology relay logic where relays and electromechanical timers were used in the 1990s because someone didn't know how to use a PLC or (my favorite) a one dollar RISC microcontroller. But if you already have the relay and that's all you need, why add an Arduino to drive the relay? If you search for "E-stop circuit" and look at the images, you'll see lots of examples and it'll make sense. There are also some standard circuits for input power disconnects (I don't go to that formality for my small CNC machines) with fuses/breakers, ON and OFF pushbutton switches that latch the ON condition until the OFF button is pressed, etc. Bruce On 11/07/2014 06:58 PM, Joe Hildreth wrote: > Bruce, > > Thanks for the information. You gave me quite a bit to chew on. Having a > computer and electronic background I tend to think of logic being implemented > via discreetly or through a micro-controller. I never really thought about > relay logic. I have never tried to implement a logic circuit with relays, so > would have to look at some samples. Off the top of my head it would seem > that driving coils in series would be an AND and the same coils in parallel > would be an OR. But beyond that no clue really. > > You said I shouldn't use IC to implement logic, but aside from the Y and !Y > (NO and NC contacts) output logic why do you recommend against it? > > Currently, I have 5Vdc, 36Vdc and 110Vac that I am dealing with. Seeing that > the 5Vdc power supply supplies my BOB, and other future devices, TTL logic > just seemed natural. > > I agree with you about the software E-Stop versus the Hard E-Stops. I will > insist to my Boys and wife that if SHTF, ALWAY hit the big red buttons! > > Thanks again for all the support, advice, direction and resources. I > appreciate it. I see I have a little reading on the subject to catch up on. > > Regards, > > Joe > > > ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
