Kicad – a small beginners project preview 

 July 12, 2018

By  Peter

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A significant part of the Kicad book I am working, I have dedicated to projects. I have planned for a total of six projects, although for practical reasons (time!) I may need to reduce that to four or five.

The project I am working on at the moment involves a simple power supply that fits on a mini breadboard. You connect a mains power brick that can output DC or AC from around 8 V to 25 V, and my supply can feed the power rails of a with 5V.

I am designing this project to be suitable for people that have just learned the very basics of Kicad. In the book, there is a tiny learning project arranged in an earlier chapter, that teaches the reader the very basics, like how to draw a wire and place components in the schematic diagram, and how to draw wires and vias in the layout editor. By stretching this knowledge just a little, the reader can create something practical, and extensible, like this breadboard power supply.

The breadboard power supply contains several stages, but the first two is where the regulation work takes place, and the rest are more like the “user interface.” In the first stage is the bridge rectifier, that consists of 4 rectifier diodes (I am using 1N4007). This is useful in case your power brick provides AC. The bridge rectifier converts that to AC. Next, is the voltage regulator. I am using the LM7805 to get 5 V out of it. The voltage regulator stage also has two decoupling and smoothing capacitors. In my prototype (photo above), I am using a 470uF capacitor on the input side and a 47uF capacitor on the output side. Both have a tolerance of at least 25V.

In the layout side of the project, the PCB looks like this at the moment:

… and here’s the 3D rendering:

Even in this small project, there’s a lot of learning to be done:

  • How to import and use third-party libraries in Eeschema and Pcbnew
  • How to find the right and place the components in Eeschema
  • How to attach the correct footprint for a component
  • How to design schematic so that it is descriptive and readable
  • How to use the PWR_FLAG component
  • How to design a PCB layout based on your indented use (in my case, make the PCB fit with a mini-breadboard)
  • How to create PCB traces of a specific width
  • How to use the Pcbnew built-in autorouter
  • How to edit the tracks created by the autorouter (though, for a simple design like this one you usually don’t have to do any more work)
  • How to place the footprints inside the PCB, optimizing for usability and performance (like minimizing track length)
  • How to create copper fills
  • How to create very simple custom footprints (I had to create a tiny opening to allow for the sliding switch’s mounting flaps to go through the PCB)
  • How to add descriptive text and decorations on the front and back of the PCB
  • How to create a 3D rendering of the board
  • How to manufacture the PCB by ordering from an online manufacturer

While there’s much learning to be done here (put yourself in the shoes of someone who has not created a PCB or used Kicad before), there are still more improvements that I (or any student) can do. For example, I can add pads where I can connect my multimeter so I can measure the current that my project draws. Then, I can improve the aesthetics by rounding all the corners. Also, I can switch the footprints for most of the through-hole (TH) components to surface mounted (SMD) to release much real estate on the PCB. The last improvement would also teach how to have several version of a PCB, drawing from the same schematic. Finally, I can also show how to use Git to source-control a Kicad Project. In fact, I kept a detailed trail of this project on Git as I was working on it, and I will be happy to share on Github.

I am eager to read your comments and suggestions on any of the above. For example, is the quality of the schematic and PCB acceptable? Are the learning objectives too many, too few, just right?


Idea, KiCad, Overview, Project, Small, Tutorial

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