Welcome to the CADSTARguys Blog - Information, hints, tips and my waffle on the CADSTAR Printed Circuit Board design suite.

Please note that all names used are completely fictitious and any thing written is my own personal opinion or knowledge and not related in any way to either my employers or their customers (or Zuken).
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Sunday, 12 February 2012

Check your dangler shape!

Hey folks, I thought I would share a warning with you about danglers.

The dangler is that little blob that gets left dangling when making a schematic connection and you double click in free space. It is designed to allow you to temporarily leave a connection dangling while you sort out something for it to connect to.

Simply put - Danglers are created when you terminate a connection in space.

I.E. you bring a connection from an IC in one corner of your schematic sheet to the other corner only to discover that you have forgotten to add the part it connects to, you double click and drop a dangler leaving the connection there - saving having to redraw it all while you add your part then continue adding the connection from the dangler.

Apart from junctions, signal references and global signals, a dangler is the only way to leave a connection without it being connected to a symbol terminal. 

So what is the warning?

Well, if you are drawing your schematic on a very fine grid, (I.E. 1th) you have to be extremely accurate connecting to symbol terminals or other connections, if you miss and inadvertently double click then you can leave a dangler instead.
Unfortunately if your dangler is the same shape as a junction then it looks the same and you do not notice that the connections are not actually the same net.

This is actually a mis-connection near the
vertical net and a dangler.

Here the vertical connection has been
pulled to the right to show the dangler.

OMG! you think - why does it let you do this? Well it lets you do this because you are not using a proper grid system and it thinks you are just dropping a dangler.

I have had designs that others have drawn that have had danglers like this and there have been net disconnects which would have made the circuit a failure had I not changed the dangler shape as one of the first things I do in a schematic.

The default shape is a circle, I disagree with this due to the above possiblilities of errors so urge you to read on and change it.

So what is the answer to this?

Well its two fold.
Firstly, do not draw your schematics on a fine (1th) grid, speaking from experience it allows them to look awful, connections are not straight as they do not line up - symbols are all on different levels etc.

Use a decent grid, if your symbols are drawn on a coarse (100th) grid then place them on that, connect to them on a minimum of 25th. (Or whatever your metric version is).

Secondly, and this is the most important bit - Change the shape of the dangler!

Do not have it the same shape as a junction point (circle) make it something obvious like a square.
Use some colour and make them Red. This way they are immediately obvious and can be immediately corrected.

From the file menu, choose Settings\Assignments\Terminal tab - in the Dangler shape box, select it and from the drop down choose square and OK that.

In Colours, select Danglers then Change Colours, select the word Danglers on the left then choose a highlight colour different to your junctions on the right.

Now you can see the difference when you have made this mistake.

Remember to make this change in your templates and symbol library assignments.


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