While we could have used a generic off-the-shelf SSOP to DIP PCB, we preferred, armed with KiCad, to design a specific one that will perfectly fit on our breadboard between our existing connectors, minimizing the amount of additional wiring on those sensitive clock signals. Also, the small PCB will act as a module by integrating terminations, power, and activation tracks without needing to reserve horizontal breadboard line for that. As a result it will be easily replaceable (or entirely skippable) in virtually no time.
The KiCad suite is splitted in several programs. "kicad" the executable is a small project manager that permits to easily launch other programs to edit the right files.
- EESchema is the schematic editor.
- CVpcb allows to assign module footprint (physical package) to schematic components.
- PCBnew is the PCB editor.
- GerbView is a Gerber viewer.
A typical workflow is to use them right in this order. You can also go back to previous steps to correct things; the changes can be correctly propagated to the next programs.
To start a project from scratch, launch kicad, press Ctrl-N and name your project (and select the directory where it will live). Now launch EESchema by clicking on its icon. The most important tools to draw a schematic are in the bar on your right and in the Place menu. Among them, you'll need most:
- Place a component
- Place a wire
- Place no connect flag
- Place net name
EESchema takes very little time to get used to. Don't hesitate to experiment and try a lot of features of this software. To speed you up, here are a few hints:
- Components are better selected, when you don't know their symbolic name, by using the library browser during insertion: click anywhere in the sheet while using the "Place a component" tool, then click on the "Select by browser" button, find the component that you want and finally click on the "Insert component in schematic" button at top-right.
- EESchema UI for edition is mostly based on a contextual menu accessible by right clicking;
- to end a wire "in the air" (for later connection); right click at the wanted position when drawing one and select "Wire end";
- to drag a wire, right click on it and select "Drag wire";
- to drag a zone, left click-and-drag to select the zone, then right click and select "Drag zone";
- dragging don't disconnect/change existing connections, while moving/orienting will disconnect/reconnect things (depending on where the module connectors end up);
- junctions are added automatically if you start/end a wire in the middle of another;
- you can edit the title block in the Page settings;
- learn shortcut keys and use them to be faster;
- note that KiCad file formats are plain text based, which is extremely cool because you can write external scripts to automatize certain tasks (moving a lot of references by a given vector comes to mind).
The schematic of our module looks like the following screenshoot.
Here is the corresponding KiCad schematic file: pcb_h100_clk_fs_49fct3805a.sch
The next article will be about schematic component to module footprint assignment. (CVpcb)