kicad-developers team mailing list archive

[José Ignacio <jose.cyborg@xxxxxxxxx>]

Pretty good summary on how net ties are implemented and are used in a
certain popular EDA package
http://wiki.altium.com/download/attachments/25079430/NetTies-and-How-to-Use-Them.pdf

On Fri, Apr 22, 2016 at 4:16 PM, Chris Pavlina <pavlina.chris@xxxxxxxxx> wrote:
> Yes, you might need a nonzero impedance between nets. Or you might not. The
> existence of a use case for something *other* than a net tie does not
> invalidate the utility of net ties...
>
> On Fri, Apr 22, 2016 at 05:14:21PM -0400, Jean-Paul Louis wrote:
>> Chris,
>>
>> It is not a hawkish way, as for EMI reasons, you might need a non zero impedance connecting the nets
>> some times a zero ohm resistor, some times an inductor and or a capacitor to cut a noise component
>>
>> Hard connection of two nets with different names is just a software issue. What I am talking about is real life PCBs.
>>
>> My $0.02,
>> Jean-Paul
>> N1JPL
>>
>>
>> > On Apr 22, 2016, at 5:08 PM, Chris Pavlina <pavlina.chris@xxxxxxxxx> wrote:
>> >
>> > "I can think of a hackish way to do it so you shouldn't implement a good, proper way"
>> >
>> > No. Please. Don't.
>> >
>> > On Fri, Apr 22, 2016 at 04:59:00PM -0400, Jean-Paul Louis wrote:
>> >> André,
>> >>
>> >> What you describe is the perfect use case for 0 ohm resistors, one resistor per net, DRC is happy.
>> >> I have seen that technique used in very high power inverters.
>> >>
>> >> Jean-Paul
>> >> N1JPL
>> >>
>> >>> On Apr 22, 2016, at 4:50 PM, André S. <list.dev.kicad@xxxxxxxxxxxx> wrote:
>> >>>
>> >>> Hi Jean-Paul,
>> >>>
>> >>> In our company we do very complex designs with different power domains where high power inverter circuits, high voltage power supplies, low voltage control circuits and analog input circuits share the same board and - regarding DC - share the same ground.
>> >>> But to achieve stable operation of the device maintaining clear ground net partitioning is one key factor.
>> >>> And with this system in mind there are use cases where up to 4 ground nets meet at one point.
>> >>>
>> >>> Regards,
>> >>> André
>> >>>
>> >>> On April 22, 2016 10:28:41 PM GMT+02:00, Jean-Paul Louis <louijp@xxxxxxxxx> wrote:
>> >>> André,
>> >>>
>> >>> Please give us an example where you would need to connect more than 2 nets.
>> >>> I understand perfectly the net tie for connecting Analog Ground to digital ground somewhere
>> >>> in a PCB, but I have hard time to figure out a case where you would need more then 2 nets.
>> >>> For AGND to DGND, a simple 0 ohm resistor will do the trick, and can be used with a resistor,
>> >>> a capacitor, a diode or an inductor without being a nuisance and no worries about DRC.
>> >>>
>> >>> My two cents,
>> >>> Jean-Paul
>> >>> N1JPL
>> >>>
>> >>> On Apr 22, 2016, at 11:34 AM, André S. <list.dev.kicad@xxxxxxxxxxxx> wrote:
>> >>>
>> >>>
>> >>>
>> >>> Hi everyone,
>> >>>
>> >>> From a users view I also would love to use net ties in Kicad.
>> >>> In my opinion they should allow to connect 2 to 4 nets on one point.
>> >>> In the schematic they could be just
>> >>> a normal component from the presentation and handling. They may just need a custom field to identify as a net tie.
>> >>>
>> >>>
>> >>> In Pcbnew they need a special handling in my opinion.
>> >>> In general on a multilayer board one should aim for a solid ground layer. However in the logical (schematic) representation it is good practice to separate analog and digital circuits. So you end up with a digital ground and an analog ground net that need to meet at one location on the board (e.g. at an ADC).
>> >>> But this connection should be not limited to a single point but more of a meeting area.
>> >>> Therefore one would need some means of allowing overlapping of these nets connected with a net tie and also raising a DRC error if the nets are not connected. Maybe a special "net connector" is required that is member of both nets?
>> >>>
>> >>> Just my thoughts on this.
>> >>>
>> >>>
>> >>> Regards,
>> >>>  André
>> >>>
>> >>>
>> >>> On April 22, 2016 3:23:12 PM GMT+02:00, Tomasz Wlostowski
>> >>> <tomasz.wlostowski@xxxxxxx> wrote:
>> >>>
>> >>> On 22.04.2016 15:11, Chris Pavlina wrote:
>> >>> You've never seen an EDA package support net ties? Or seen them used
>> >>> to
>> >>> separate logical power planes? Quite common, really...
>> >>>
>> >>> Me too.
>> >>>
>> >>> IMHO it can be done without any changes on the eeschema side by adding
>> >>> a
>> >>> special component to the standard library (just like GND/power ports).
>> >>> PCBnew could interpret it as a zero-sized copper pad. Some DRC
>> >>> modifications would be needed to correctly take into account clearances
>> >>> of the nets connected by a tie.
>> >>>
>> >>>
>> >>> Tom
>> >>>
>> >>> I'd _love_ to see proper net tie support in KiCad. :)
>> >>>
>> >>> On Fri, Apr 22, 2016 at 09:04:10AM -0400, Wayne Stambaugh wrote:
>> >>> On 4/20/2016 4:00 PM, Simon Richter wrote:
>> >>> Hi,
>> >>>
>> >>> as wxWidgets is getting on my nerves with editing widgets in the
>> >>> pin
>> >>> table not rendering properly, I've started on support for net ties.
>> >>>
>> >>> In the current iteration, they would be placed the same way as
>> >>> junctions.
>> >>>
>> >>> Rules:
>> >>>
>> >>> - Any wire or pin connected to a net tie is in a separate net
>> >>> (unless
>> >>> connected elsewhere).
>> >>> - The net tie maps to a pseudo-pad that all three nets need to be
>> >>> connected to.
>> >>> - Connecting the nets there does not give a DRC error -- anywhere
>> >>> else
>> >>> will.
>> >>> - The pseudo-pad can be placed on a regular pad if it is on one of
>> >>> the
>> >>> nets connected to the net tie.
>> >>>
>> >>> Use cases:
>> >>>
>> >>> - Analog and digital supply planes connected with a trace, but
>> >>> otherwise separate
>> >>>
>> >>> I'm going to put my EE hat on and say that if you connect two power
>> >>> planes with a trace then they are the same plane no matter what you
>> >>> called them in your schematic.  A more typical solution in this case
>> >>> would be to physically separate them by some type of component or
>> >>> components.  Usually inductors or 0 ohm resistors (aka jumpers) are
>> >>> used
>> >>> in this situation depending on what you are trying to accomplish.
>> >>>
>> >>> - Current sense resistors between a supply rail and a load
>> >>> - Decoupling capacitors.
>> >>>
>> >>> I can see the decoupling capacitor use case where you want to tie a
>> >>> cap
>> >>> to a specific component power pin.
>> >>>
>> >>>
>> >>> I've added UI[1] and save support in eeschema already, still needs
>> >>> mapping to the netlist and pcbnew
>> >>> support.
>> >>>
>> >>>
>> >>> Are you aware that changes to the current schematic file format are
>> >>> forbidden until we (I) finish implementing the new file format?
>> >>> This
>> >>> was discussed fairly recently so everyone should be aware of this.
>> >>> In
>> >>> any event, you should have gotten input from the development team
>> >>> before
>> >>> heading down this path.  This is good advice for any developer.
>> >>> Even I
>> >>> solicit input on new features or large changes because other devs
>> >>> always
>> >>> seem to think of things I didn't.
>> >>>
>> >>> I don't have a strong opinion one way or the other about this
>> >>> feature.
>> >>> On the surface it does seem useful but I've never seen any EDA
>> >>> product
>> >>> support this so board designers may not understand why they would
>> >>> want
>> >>> to use it.  Any one else have any thoughts on this?  You may also
>> >>> want
>> >>> to check with the users to see if it's something that they would
>> >>> even use.
>> >>>
>> >>>
>> >>> There doesn't appear to be a real standard on how to represent net
>> >>> ties
>> >>> in the schematic, though. A design note[2] from Linear Technologies
>> >>> uses
>> >>> 45 degree angles on wires to make it look really intentional that
>> >>> the
>> >>> wires should meet in the same spot, but that would be a major
>> >>> hassle
>> >>> both to implement and use.
>> >>>
>> >>> For now I've gone with a larger dot, but that is very unintuitive.
>> >>> Printing net names next to wires is difficult, because these are
>> >>> still
>> >>> wires only. Numbers next to the wires might be doable, but
>> >>> confusing, so
>> >>> if anyone has a good idea how to represent them, please speak up.
>> >>>
>> >>> How about a different color dot or a different shape.  A different
>> >>> shape
>> >>> may be better for users who are color blind.
>> >>>
>> >>>
>> >>>   Simon
>> >>>
>> >>> [1] http://psi5.com/~geier/net-tie.ogv
>> >>> [2] http://cds.linear.com/docs/en/design-note/dn434f.pdf
>> >>>
>> >>>
>> >>>
>> >>>
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>> >>>
>> >>>
>> >>>
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>> >>>
>> >>>
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>> >>
>> >>
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