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How to deisgnate a GND strip? (Read 10971 times)
bwims
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How to deisgnate a GND strip?
Oct 8th, 2007 at 6:38pm
 
Hi,

I used the TinyCad Earth symbol for a number of connections and then created a terminal pin which was also connected to Earth (GND)  I dedicated a strip for this terminal, yet when I linked all of the earth points to it, the "Draw NET Errors" button highlighted all but the one with a direct connection as errors.

Is there a special way to designate a GND strip?

Thanks for a great product,

Brian
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Roger Lascelles
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Re: How to deisgnate a GND strip?
Reply #1 - Oct 9th, 2007 at 4:29am
 
Hello Brian

The simplest cause is a TinyCAD earth symbol shifted up or down so pin or wire doesn't actually contact the end of the symbol.  The second cause is described in the rest of this post.

TinyCAD had an awful connection bug.  TinyCAD V2.60.01 practically eliminated the bug.

When exporting the netlist, TinyCAD detects connections by looking for wires which are close to terminal or pin ends. TinyCAD uses different code to detect wire to pin joins during editing, so a join can behave like a join on screen, but be ignored by the netlist exporter!

To minimise the problem:

1. Draw your schematic and library components with Snap To Grid and Fine Grid turned on. Now the components and the drawing match.

2. Schematic symbols you get from the Net can be off-grid and prone to connection troubles.  V2.60.01 greatly reduced sensitivity to off-grid items, but not totally.  You may need to re-place pins in the library editor to get them on-grid.

3. In TinyCAD, do "Special->Check Design Rules" and tick only "Unconnected Items".  Run the check and inspect all the error points to find out what will not be joined in the netlist.

4. Click on the power tool button and place a brand new symbol on the wire or pin - don't move an existing symbol to a new location and don't run the wire to the pin.

With the above precautions, I  see about one connection problem a year - and its easily found with the TinyCAD connection check.
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bwims
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Re: How to deisgnate a GND strip?
Reply #2 - Oct 13th, 2007 at 4:27pm
 
Thanks Roger, that solved it!  Brilliant!

Brian
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bwims
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Re: How to deisgnate a GND strip?
Reply #3 - Oct 20th, 2007 at 12:40pm
 
Hi Roger,

Although the connection problems are solved, my original question still isn't.  If I use the TinyCad Earth symbol at several locations, there seems no way to make the Autorouter realise that they all need to go the the designated GND strip. How do I do this without connecting all the earth points on the schematic?

Many thanks,

Brian
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Roger Lascelles
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Re: How to deisgnate a GND strip?
Reply #4 - Oct 21st, 2007 at 9:15am
 
Hello Brian

I'll discuss the issues and you can tell me if I miss your specific problem.

TinyCAD, like any schematic editor, lumps all common net points together in the netlist - whether connected by wires or net symbols like the GND symbol.  On the VeeCAD menu, go Netlist->View and select the Nodes tab.  Find the GND node in the list.  If all GND pins are listed, then all is OK at the TinyCAD end - if not let me know.

To tell the VeeCAD router that you have reserved an unused strip for GND, you have to connect it to ground yourself.  Turn on the connectivity check and find a component pin which connects to GND.  If needed, remove any red error circle on the pin by placing a break somewhere to the left of the pin.  Our pin and its strip belong to ground.  Link the strip to your reserved GND strip, or place a pair of wire symbols to make the connection.  Use Trace Net to prove that the track now belongs to GND.  Now autoroute the GND net or the whole layout.

Note that a VeeCAD wire symbol which displays "GND" may not be connected to the GND net, because VeeCAD matches wire symbols with identical text and does not use the text as a net name.

The router uses the shortest possible links.  If you have a common ground strip along the length of your layout, the router will link only the nearest GND strips to it, with more distant strips connecting to intermediate strips.  This gives a compact layout, but for some layouts like high speed HC logic, power amplifiers etc you may want to manually connect to a specific ground track.

Hope this helps!
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bwims
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Re: How to deisgnate a GND strip?
Reply #5 - Oct 21st, 2007 at 12:19pm
 
Many thanks for replying Roger!  I will definitely try that for my next project. I used a workaround for now which involved putting a long horizontal connection through the schematic which is connected at one end to chassis ground, and connecting all the earth points to that. Then I designated GND as a 1_PIN symbol and put it on my GND strip, and everything connected to it correctly.

Will your method work with the built in TinyCad power earth symbol, or does it need to use a selected GND symbol?

Thanks again,

Brian
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Roger Lascelles
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Re: How to deisgnate a GND strip?
Reply #6 - Oct 21st, 2007 at 2:09pm
 
Placing a grounded pin on your strip was an effective way to tell the router you had a ground strip.  Exactly the same effect as the link / wires method I mentioned.

TinyCAD and VeeCAD do not use specific net names, so you can say "GND", "0V", "EARTH" etc as you wish.  When you use a TinyCAD power symbol and select the EARTH shape, that just sets an image - you still have to enter a net name.  Power symbols and wire labels both produce net connections - the only difference is the image shown.

Finally, all nets are treated identically by TinyCAD and VeeCAD and all schematic and autorouter techniques we have discussed will work for any net - eg power, signal etc.
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bwims
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Re: How to deisgnate a GND strip?
Reply #7 - Oct 21st, 2007 at 6:11pm
 
Many thanks Roger!  That's very helpful.

Brian
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