Archive for April, 2016

Weekly Wrap 4 – 10 April 2016

Cheesecake danish

CSIRO notebook

Atten­ded a car acci­dent on Monday with the SES.

Baked my first suc­cess­ful Dan­ish using an online recipe after two failed attempts fol­low­ing a recipe book. We ate one and gave one away to my Grandfather.

Designed my first PCB using KiCad and wrote up the exper­i­ence.

Had my new engin­eer­ing note­books delivered, offi­cial CSIRO stock. I had a ter­rible time try­ing to find a decent book, my cur­rent one is an art book I picked up from Office­Works and it wasn’t ideal. The cur­rent book has a few pages left, I’ll prob­ably trans­ition over to a new one in a week or two.

Using KiCad

I have been exper­i­ment­ing this week with cir­cuit design and pcb lay­out tools. My exper­i­ence is with Altium but the price is rather hefty for my fairly simple require­ments and while I have used Altium for a few years I never actu­ally liked it, there are a lot of issues with the sys­tem. I con­sidered the vari­ous online tools and Eagle before decid­ing to give KiCad a go.

KiCad is an open source bundle of tools which has been rap­idly increas­ing in qual­ity over the last few years. CERN is provid­ing pro­fes­sional devel­op­ment sup­port and they have recently trans­ferred from a ‘build the source’ release struc­ture to stand­ard point releases.

I have played with KiCad for most of the week. It is good, I could do everything I needed to for the basic board I was doing, but some of it was a struggle. There are a lot of rough edges, how­ever the com­munity seems strong and most of the issues I encountered are in the pro­cess of being fixed.

There are sev­eral pro­jects under the KiCad ban­ner which loosely inter­op­er­ate, it seems they have had vary­ing amounts of coordin­a­tion over the years. Kicad itself is a pro­ject man­ager and applic­a­tion laucher. Ees­chema is the schem­atic design soft­ware. Pcb­new does the PCB lay­out. There are other tools I haven’t played with yet, such as a ger­ber viewer.

One of the issues is the cooper­a­tion between these applic­a­tions. For example the con­trols such as key­board short­cuts and mouse beha­viour are incon­sist­ent (This is flagged to be fixed by intro­du­cing a global short­cut man­ager). For a while (since fixed) pcb­new had pan­el­iz­a­tion fea­tures avail­able when launched stan­dalone but not when launched from within kicad . These sort of prob­lems mean that it feels more like using sev­eral dif­fer­ent pro­grams than a uni­fied suite.

Break­ing news

I have pub­lished a writeup of the board I designed, at https://​david​.tul​loh​.id​.au/​g​r​i​d​e​y​e​-​u​sb/.


Eeschema screenshot

Eeschema is nice and familiar, you can place parts, connect wires, create named nets etc. I had a very simple five component board so had no need of the advanced features. However there was obvious functionality for buses and a fair bit of support for nested sheets. There is annotation tool to name your parts and a basic rule checker to catch mistakes.


A nice bonus for Eeschema is the ability to have two names on a net. This is a bit controversial, Altium forbids it but I like it. Some times a line has two roles, such as being the MISO communication line during programming and the I2C interrupt line during normal operation. I like being able to create a named net for each role and connect both to the pin of the chip. The PCB layout program needs a single name, Eeschema handles this by arbitrarily picking one of them.

Missing Feature

Altium has a feature they call directives. This allows a pair of wires to be identified to be routed as a differential pair. You can also specify net classes, so as to specify increased track widths for the power rail or the required clearance on a high voltage track. KiCad does allow this to be done in Pcbnew but I feel the schematic, as the documentation for the design, should contain this information. This is particularly important if the layout and design are performed by different people.


Eeschema's use of dragging with the left mouse button is odd. In most applications this would perform a group select, in eeschema it selects and begins to move the components. Copy/paste is done by holding down shift before doing a selection. The oddness and learning curve aside, this doesn't scale well. There is no way of selecting a group of objects so you can't do a group delete, you can't change the properties of a group or resize multiple wires together. Using the copy/paste you can't double check what you have selected before doing a copy, multiple pastes require the full process to be run again and you can't change sheets. The move is still the action regardless of the tool selected, so dragging with the wire tool actually does a select/move and placing a box like a sub-sheet must be done with two clicks not a drag.

I suspect the select behaviour will be changed in the same batch of work as the shortcut improvements.


I should open by saying I couldn't really get my head around the schematic libraries. My understanding is that a library file can hold multiple components but I couldn't figure out how to put a second component into a library file. I did see notes suggesting that you merge two libraries by editing them by hand.

Several people have created their own tools to try and assist managing libraries. The existence of these tools indicates that many others have also encountered problems.

There is hidden magic behind the library process. For example to create a power component, basically a power net flag, the pin must be hidden. The pin still gets a wire connected to it but if it is not hidden it doesn't connect to the power net and you get unconnected errors when running the rule check. This isn't documented, the nice folks in the IRC channel explained it to me.

There is also documented hidden magic where some parts, fortunately none I used, have hidden VCC pins so they magically get the power rail without cluttering your schematic. Which is not so useful in the modern environment of multiple signal levels.

The developers are well aware of all of these issues, half the roadmap entries for eeschema are related to component editing. The plan seems to be to migrate the backend of the schematic library to the pcb library file format and work. Then build better editing tools on top. The PCB library tool is a significant step forward.


Eeschema screenshot

It took me a while to real­ise that there are actu­ally three dif­fer­ent PCB pro­grams bundled into Pcb­new. They are lis­ted in the view menu as three dif­fer­ent dis­play modes: default, OpenGL, and Cairo. This is not, as you might expect, just a dif­fer­ent dis­play engine. Some fea­tures are not avail­able in all modes and some fea­tures work dif­fer­ently depend­ing which mode you are in. I found Cairo ran very slowly on my poor ancient laptop so I just used default and OpenGL.

Dif­fer­en­tial rout­ing is a rel­at­ively new fea­ture and is only imple­men­ted in OpenGL. In the default view the fea­ture on the menu is simply dis­abled, grayed out, no feed­back is provided as to how to enable it.

There are other, lesser issues:

  • In GL mode the scroll bar arrows don’t work, drag­ging does.
  • Rub­ber band drag mode only works in default mode.
  • In nor­mal mode delet­ing a track deletes the attached via, in GL mode it does not.
  • In nor­mal mode the start track short­cut starts a track imme­di­ately, in GL mode it waits for a click.

There is a 3D model fea­ture which uses VRML world files for each part. How­ever it only sup­ports the sub­set gen­er­ated by wings3d, more com­plex files silently fail. Extend­ing this to other model types is on the roadmap.

Some other stuff feels a bit incomplete:

  • Hid­ing a cop­per layer still shows the pads.
  • There is a “Hide all cop­per lay­ers but act­ive” option for single sided work but it doesn’t hide the other side’s silkscreen.
  • The rule-check doesn’t enforce track width.

Finally the lib­rary man­age­ment is bet­ter than Eescheema’s but still needs a lot of work.

  • Rel­at­ive paths require manu­ally using an envir­on­ment vari­able, which was lis­ted in the Ees­chema lib­rary man­ager but not Pcbnew’s.
  • There is a plu­gin to add git­hub based repos­it­or­ies, but the option is lis­ted even if the plu­gin is not installed.
  • There is a plu­gin to add git­hub based repos­it­or­ies, not git based, it uses a git­hub webpage URL.
  • Adding a lib­rary doesn’t check that the lib­rary exists, works or is valid. An error is shown later when you try and use it.
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