Discussion:
Same net but different net class with Eagle
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Fabrizio Boco
2019-04-16 06:38:49 UTC
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I have a trace which powers an external device and with a large size because it carries a relative high current (more than 1A).
Along this trace I have a small value resistor to monitor the flowing current.
The resistor is connected to an ADC to measure current. The traces between the resistor and the ADC can be smaller than the power traces because not much current flows there.
I am not able to use two different net classes for the power trace and for the ADC traces. A soon as I change the class of the power trace, the sensors traces get the same net class and viceversa.
I have also tried to put a 0 ohm resistors along the sensor traces but this doesn't help neither.
Can anyone help me with this issue?
Thx

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Paul Romanyszyn
2019-04-16 15:30:28 UTC
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Post by Fabrizio Boco
tried to put a 0 ohm resistors along the sensor traces but this doesn't help neither.
You have to use a different net name between 0 ohm and sense resistor so
it can have the different class.
Paul R
Chuck Huber
2019-04-17 18:00:17 UTC
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Fabrizio,

shorts.lbr can be found at
http://www.diymodules.org/eagle-show-library?type=usr&id=1012210749&part=shorts.lbr

HTH,
    - Chuck
Fabrizio,
Look in the shorts.lbr file.  It consists of two SMD pads that
overlap.  By putting a short in series with your smaller resistor, it
forms two different nets.  The net between the short and the resistor
could be assigned a different class allowing the narrower trace.  I
can send a shorts library to you.  Olin Lathrop is the original
author, and I've added a couple of my own.  Olin has published it on
the Internet, which is where I found it years ago.
My primary use of shorts is to connect different grounds together. 
i.e. I'll have a DGND, AGND, and HVGND representing grounds used in
different areas of a design (digital, analog, and high voltage).  In
the end, all these grounds need to be connected together.  I'll
connect DGND to GND through a short, then AGND to GND, and HVGND to
GND.  Just plain old GND will be routed back to the battery, or power
supply or whatever.
Of course, you could use the narrower trace just as you have it now. 
When you do the DRC, you can approve the error it generates and it'll
never bother you again... at least until you move it.
HTH,
    - Chuck
Post by Fabrizio Boco
I have a trace which powers an external device and with a large size because it carries a relative high current (more than 1A).
Along this trace I have a small value resistor to monitor the flowing current.
The resistor is connected to an ADC to measure current. The traces between the resistor and the ADC can be smaller than the power traces because not much current flows there.
I am not able to use two different net classes for the power trace and for the ADC traces. A soon as I change the class of the power trace, the sensors traces get the same net class and viceversa.
I have also tried to put a 0 ohm resistors along the sensor traces but this doesn't help neither.
Can anyone help me with this issue?
Thx
--
https://www.element14.com/community/message/274385
Chuck Huber
2019-04-17 17:54:40 UTC
Permalink
Fabrizio,

Look in the shorts.lbr file.  It consists of two SMD pads that overlap. 
By putting a short in series with your smaller resistor, it forms two
different nets.  The net between the short and the resistor could be
assigned a different class allowing the narrower trace.  I can send a
shorts library to you.  Olin Lathrop is the original author, and I've
added a couple of my own.  Olin has published it on the Internet, which
is where I found it years ago.

My primary use of shorts is to connect different grounds together.  i.e.
I'll have a DGND, AGND, and HVGND representing grounds used in different
areas of a design (digital, analog, and high voltage).  In the end, all
these grounds need to be connected together.  I'll connect DGND to GND
through a short, then AGND to GND, and HVGND to GND.  Just plain old GND
will be routed back to the battery, or power supply or whatever.

Of course, you could use the narrower trace just as you have it now. 
When you do the DRC, you can approve the error it generates and it'll
never bother you again... at least until you move it.

HTH,
    - Chuck
Post by Fabrizio Boco
I have a trace which powers an external device and with a large size because it carries a relative high current (more than 1A).
Along this trace I have a small value resistor to monitor the flowing current.
The resistor is connected to an ADC to measure current. The traces between the resistor and the ADC can be smaller than the power traces because not much current flows there.
I am not able to use two different net classes for the power trace and for the ADC traces. A soon as I change the class of the power trace, the sensors traces get the same net class and viceversa.
I have also tried to put a 0 ohm resistors along the sensor traces but this doesn't help neither.
Can anyone help me with this issue?
Thx
--
https://www.element14.com/community/message/274385
fabboco
2019-04-18 11:07:54 UTC
Permalink
Hi Chuck,
Thank you very much. That is exactly what I was looking for.

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