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 Post subject: What is the "right" way to handle zero-ohm resistor/jumpers?
PostPosted: 18 Aug 2015, 00:33 
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Joined: 16 May 2015, 00:35
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So I have a net and I want to use a zero-ohm resistor with it. Both sides of the resistor are going to be attached to the same net, obviously. That's fine except when I run the net connectivity test, it tells me the net is broken. It is not wrong, of course, but it isn't exactly right either. It occurs to me that perhaps there's a better way to do this? Is there some way I can put an exception so it stops telling me something's wrong? Or is there some way to convince it that, electrically speaking, a zero-ohm resistor is the same as having a solid trace?


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 Post subject: Re: What is the "right" way to handle zero-ohm resistor/jump
PostPosted: 18 Aug 2015, 02:48 
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Joined: 26 Mar 2015, 15:27
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I'm not sure I understand. A zero ohm resistor is exactly the same as any other resistor. Maybe you can post a sample file that illustrates the problem?


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 Post subject: Re: What is the "right" way to handle zero-ohm resistor/jump
PostPosted: 18 Aug 2015, 03:33 
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Joined: 16 May 2015, 00:35
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Well, it is an it isn't. Which is why I said Diptrace isn't handling it wrong, but not exactly right either.

Physically, it is the same as any other resistor, but electrically (and logically), it is not a resistor at all, it is a shunt or, again electrically speaking, the exact same as a trace.

Assuming this is just a limitation of the software, then to me the logical way to handle it (for future revisions) would be for the resistor to be treated as though it isn't even there (by the connectivity checks) if both sides of the resistor are connected to the same net, and for it to be treated as a blocking feature if they are connected to different nets. This would handle the two most common uses for a zero-ohm resistor.

I shouldn't have to draw anything to illustrate my point. Say I route in such a way that two ground plane islands are created and I'm space constrained and I simply can't get the two islands to connect and I don't want to create a multi-layer board just for this. A simple way out of this is to create a "bridge" by laying a zero-ohm over a breaking trace, thereby joining the two islands. We can logically see that, electrically speaking, there is no connectivity issue... yet the software says there is.

That's just one example. I can't possibly be the only one that's run into this, which is why I figure there must be something I'm missing.


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 Post subject: Re: What is the "right" way to handle zero-ohm resistor/jump
PostPosted: 18 Aug 2015, 05:00 
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Joined: 26 Mar 2015, 15:27
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bcsteeve wrote:
I shouldn't have to draw anything to illustrate my point.


You posted this in schematic capture, and it doesn't seem like it has anything to do with schematic capture, so it's confusing what you're actually trying to do. Despite that, I think I understand.

Add your resistor pattern where you want it. Draw ratlines from the resistor pads to your ground net. Draw a jumper wire between the resistor pads. Update the copper pours. Voila.

If you would prefer that it doesn't throw an "unknown component" error when you check against the schematic, simply add a resistor to the schematic in parallel with your ground net. Then in your PCB layout, add a jumper wire between the resistor pads. Everything will be happy. If I did this on my own schematic, instead actually drawing it in parallel with a ground net wire, I would probably drop two ground symbols on my schematic and draw the resistor between them, just to make it obvious what I'm doing.

Hope that helps.


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 Post subject: Re: What is the "right" way to handle zero-ohm resistor/jump
PostPosted: 18 Aug 2015, 13:46 
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Joined: 16 May 2015, 00:35
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Yes, I posted in schematic capture. Is there a better forum for it? It all starts in schematic capture. The resistor is in the schematic, afterall. Then the layout is updated from schematic. Otherwise if I just add the pattern, won't it disappear when I update from schematic?

So I think it is this "jumper wire" concept I'm missing. I'll look into that, thanks.


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