KiCad

Roger Cheng

First OSH Park Order Arrived

My first KiCad project was sent to OSH Park almost two weeks ago, and my digital design is now back in my hands in physical form. It is really quite exciting to hold in my hands a circuit board I designed. Three copies of it, in fact, as per usual OSH Park practice.

The first order of business is to check for simple mistakes. I pulled out my multimeter to verify that I have good connection between all the VCC pins to the VCC plane, and similarly all the ground pins are connected to the ground plane. Then I brought up my design in KiCad and checked continuity for the pins I designated. I don’t know if I exhaustively checked them all, but a large portion were verified.

Once I’m satisfied my design has been faithfully produced by KiCad, it was time to pull out the soldering iron. I thought I’d do some incremental tests – solder a subset of components to verify the subset of LEDs light up correctly – but I was eager to see it all light up so I went ahead and populated the whole board. The legs of the 2N2222A transistors in their TO-92 package were closer together than I’m used to in my soldering projects, but other than that challenge it was all simple and straightforward soldering.

Populated LED board

And finally, the moment of truth. I was working in Tux-Lab and a bunch of nearby guys gathered around to see me power up the board for the first time.

<drum roll>

It’s alive! The test pattern already programmed into the PIC started cycling through the LED display. This success is a great confidence-builder. I had fully expected to find problems with the board that I would have to fix in KiCad and send back to OSH Park for another set of circuit boards to be produced. The only problem I encountered was the PICkit 3 does not fit nicely alongside the power connector. I could make it work by making them wedge together at an angle. Neither were happy with it but it should be relatively rare to have the programmer attached.

Well, I guess break time from PIC software is over – I no longer have an excuse to play with other projects. The task of writing my I²C driver routine for this display is back on the to-do list.

Roger Cheng

Placed First OSH Park Order

After several revisions – including several PCB layouts that were restarted from scratch – I’ve learned a lot about using KiCad.  I don’t know for sure it’s all going to work, but I feel confident enough to make the first revision of my board. If it comes back and the board doesn’t work, I’ll have new lessons to learn. Or if it does, I celebrate!

Off to OSH park!

They have a very KiCad-friendly pipeline that accepts the PCB data file directly, no file conversion or data export necessary. I was worried about file format compatibility since I am running the latest nightly build and OSH Park only officially supports the most recent stable build. Some people have reported issues, but in my case it seemed to have gone through successfully.

The OSH Park verification screen is a great confidence builder. They took my file and generated these images for me to look over. This is awesome! I can clearly tell that it is my design and it generally looks fine. The resolution is a little lower than I would have liked. It is starting to be difficult to make out individual traces on my board, it would obviously be impossible to do so on a large complex board. But I assume detailed checks are not the point, we just need to verify we haven’t uploaded the wrong board and that nothing’s fundamentally broken in OSH Park’s interpretation of it.

OSH Park Verify

Upon checkout I was surprised that two Teensy boards were available as add-ons to my purchase. I don’t know why the circuit board fabrication shop is selling their own edition of the Teensy board, but since I had been thinking about buying one to play with anyway, it was an easy impulse buy to add a Teensy LC to the basket.

And now I wait. The board should arrive in two weeks and I won’t know what I need to fix in KiCad until I get the board and put it to (in)action. This puts a hold on the PIC micro controller hardware side of the project, and I can turn my attention to something else for a while.

(The work described in this blog post are publicly available on Github.)

Roger Cheng

Refining the LTC-4627JR Driver Board

I am lucky to have some local people who have worked with KiCad and were willing to help a beginner. I’ve asked for tips before I started, but much of them didn’t make sense until I had a run with my own project. Now I can go back and ask the questions again, and with some firsthand experience to anchor the concepts, the answers make much more sense.

I learned that there were flaws in my schematic. I had connected my PIC micro controller output pin directly to the base of a 2N2222 transistor. I shouldn’t directly expose the 2N2222 to the full voltage and current from the PIC. It is not an immediately catastrophic condition – I got my bread board prototype up and running without them – but in their absence the transistors end up burning much more power than necessary and likely reduces their lifespan. So the schematic receives five additional resistors, one for each transistor.

I also neglected a pull-up resistor recommended for the Vpp pin in the PICkit 3 manual. Again, my bread board seems to run OK without it, but it’s better to follow spec.

These six additional resistors complicate the PCB layout. Fortunately, I received some useful tips here as well. I chose one design pattern to practice: separate the front and back layers into vertical and horizontal traces. This requires copious use of vias to connect these individual segments into a full connection. I had been concerned that every via is a connection and a potential source of failure, but I’ve been reassured that’s not a concern. When the horizontal/vertical division, wire traces can cross paths in a safe manner because the directions keep those traces isolated.

I also learned the concept of a fill zone, which makes it easier to distribute the voltage input and ground to all the components on the chip. Instead of running individual narrow traces that might not be able to handle the full power, they are distributed across all the spare surface area I can reach. I use my front copper layer to distribute power, and the back copper layer became the ground layer.

The downside is that, by breaking horizontal and vertical onto their individual layers, it because much more difficult to visually follow the logic of a board. A situation not helped by the fill zones, which obscure other layers so I have to look at the front and back separately.

PCB5 F.Cu

PCB5 B.Cu

The upside of this approach is that it makes layout much easier to do. And despite the visual appearance, the net result is actually simpler despite being broken up across the two layers. Before learning these techniques my trace count was in the 180-200 range. Now it sits at 164 and this is after adding six resistors to the circuit complexity.

These are quite satisfying steps forward.

(The work described in this blog post are publicly available on Github.)

Roger Cheng

A Beginner Learns PCB Routing is Hard

Drawing up the circuit diagram/schematic was a new thing, but I got through it with minimal headaches and was feeling pretty good about using KiCad. After I was done with the first draft, I moved on to route all the connections to be placed on the printed circuit board (PCB). Doing this, I get firsthand experience that wire routing is a hard problem.

The first few connections were easy, but then it got progressively more difficult as I struggled to find a route for the later connections. The center of the board inevitably became a traffic jam and I started having to go around the jam. Every track that go around the outside perimeter of the PCB is a surrender that I couldn’t find a better way.

In addition to the traces going around the outside perimeter, another way to quantify my frustration with my circuit is the number of tracks in the KiCad PCB file. This is a number easily readable in the text format save file.

Fortunately, it doesn’t cost anything to learn by doing, redoing, and repeat.

The first attempt was a hopeless mess and I had to abort before I could connect everything. Here is version 2, where everything is actually connected with almost 200 tracks and multiple traces that go around the perimeter in a last-ditch effort.

LTC-4627JR I2C PCB v2

Version 3 changed the layout of the components in an attempt to make routing simpler. Moved the LEDs to the top, etc. It felt cleaner but is still quite a mess. I managed to avoid long traces that went around the left and right perimeters, but I still needed several at the bottom perimeter. And the track count didn’t improve by much – still just under 200.

PCB Route v3

Version 4 had the same basic layout as version 3 but I’ve learned to recognize a few signs of upcoming problems and could work to avoid them. The result had a further reduction in tracks, almost a 10% cut down to under 180. Plus I needed even fewer perimeter rescue paths.

PCB 4

The English language has the colloquialism “Paint yourself into a corner” and this is a very similar thing – it’s very easy to route yourself into a situation with no way out. I wish I could condense the lessons I learned into a summary here, but so far it’s just a lot of trial-and-error. Try something until I run into an obstacle, then try to figure out how to get out of this mess.

At this point the only words of wisdom I could offer is – dive in and try. It won’t work, but you’ll learn. Try and try again until you get good enough to get to a point where everything is connected, however inelegant it might be, and keep iterating to improve from there.

(The work described in this blog post are publicly available on Github.)

Roger Cheng

KiCad Circuit Diagram Schematic Editor (Eeschema) Amateur Hour

The KiCad Getting Started guide only covers the basics, but it’s enough to let the user embark on exploratory adventures to learn the rest of the tool piece by piece. I know I don’t have the knowledge and experience to do a good job at circuit design, but I’m a believer that such knowledge and experience is built up by learning from mistakes. So: let’s dive right in and try to implement the circuit board for my LTC-4627JR driver project and see what we learn.

The circuit diagram portion was relatively straightforward. Most of the lessons in the Getting Started guide applies, up to and including how to build a custom component for my schematic because the LTC-4627JR was not in the KiCad standard library. Somebody had built a library of components that included the LTC-4627JR, and made it available on Github. But this is a learning exercise and I wanted to learn how to do it myself.

The PIC16F18345 was not actually in the KiCad library, but a sibling part PIC16F18344 was available with a 20-pin DIP footprint, which is what I want right now. However, the eventual goal is to go to the surface mount version of the part and I hope I’ll be able to find another substitute with the same 20-pin SMD footprint.

There was no specific KiCad part for the 2N2222 transistor, but there are generic NPN transistors and I think that’s good enough. I was puzzled by the large number of options until I figured out they were different combination of a transistor’s pins. The three pins were labelled in order of pin number. So the variant tagged “BEC” has the base on pin 1, emitter on pin 2, and collector on pin 3. The “BCE” variant has the latter two pin swapped, etc. Looking at my 2N2222, I decided to use the EBC variant because that’s the order I see in the Wikipedia article.

The resistors were straightforward, as were the two I/O headers on the board. A four-pin connector for power, ground, and the 2 I²C wires. The five-pin connector is for the PICkit 3 to perform in-circuit programming.

From looking over schematics in the past, I got the distinct feeling of a stylistic convention for laying things out. Much like there are conventions for software source code. But a gut feel is not enough – I needed help from somebody to concretely spell out the rules. A web search for “circuit diagram conventions” pointed me to this article on Electronics StackExchange.

Armed with the list of conventions and a few hours to bump my head in KiCad, I got a passable basic schematic.

LTC-4627 I2C schematic

(The work described in this blog post are publicly available on Github.)

Roger Cheng

Notes on KiCad “Getting Started” Guide

To get started learning KiCad, I tried the obvious thing first: Go to the KiCad web site, click on “Documentation”, and click on “Getting Started”. This beginner’s tutorial walked me through drawing the circuit diagram schematic and then turning that abstract design into something that can be fabricated on a circuit board.

Because circuit board design is a fairly esoteric field, a tool like KiCad also has lots of terminology that’s a little tough for a beginner to digest. Thankfully the getting started guide helps put a lot of things in the context of the basic design process, so I could see words and phrases used in context and try to derive their meaning that way.

A lot of areas in KiCad were not covered in the tutorial, but that is to be expected. I just wanted the bare bones to start and I can explore other venues later.

The downside of learning a piece of software in active development is that it is still changing, throwing the tutorial out of date. Some menus were moved, though thankfully the keyboard shortcuts seem to have stayed consistent. Some parts of the software hasn’t only been moved, their icons had been changed. The tutorial occasionally gave instruction as “Click on the button with this icon” so when the icon changed, the beginner is lost.

(Workaround: Keep reading the tutorial to get a feel of what the next step is, what menu might pop up, etc. Then mouse-over each of the icons on the page and look for names that sound like they might be related to the activity.)

There were many of those minor annoyances, and there was one major annoyance. The guide had a section on how to generate a Bill of Materials (BOM)  using a plug-in module. The plug-in module was not installed at the location the guide stated. I went hunting on the KiCad Github repository to find the file, and once I downloaded it, it didn’t work with a bunch of error messages I had no hope of understanding.

Fortunately, BOM generation is not yet a priority for my usage. And I got far enough to draw a simple schematic and turn that into a simple circuit board design.

That’s good enough for a start.

KiCAD Tutorial

 

Tutorial circuit board

Roger Cheng

New Adventure in Circuit Board Design with KiCad and OSH Park

There are several things I can work on for my PIC-controlled LED practice exercise. The software is far from done, with lots of features I still want to implement. But I’m turning my focus to the hardware for the moment. Now that I’ve built a few iterations of my circuit on the prototyping breadboard, I have some confidence it’ll work for whatever software I write. So I’m going to look into translating the simple design into an actual circuit board.

When I started learning electronics many years ago this was a daunting step that I never took. Back then making my own circuit board meant buying sheets of copper-clad circuit boards. I would then need the ability to drill precise holes in this board for the component pins and I would need to etch my circuit into the copper layer. Either via precise mechanical removal or a chemical etching processes. This DIY fabrication was required because it was not economical for commercial circuit board manufacturers to do low-volume production for hobbyists.

Thankfully, the internet has enabled a solution. We now have circuit board fabricators who batch up many little projects from around the world into low volume production runs. The local electronics hobbyists speak well of OSH Park, who bills by the square inch and each order gets three copies of the circuit board. There’s enough demand for these services that OSH Park has competitors, both domestic and overseas, but I’m happy to start with the known quantity that has worked for people I’ve talked to.

The downside for this economical service is time: because of the job batching pipeline, it takes around two weeks from order submission to parts in my hand. Since I have more time than money to devote on these learning projects, I’m happy to accept this trade-off. It also means I should start the first iteration of my circuit board now: once I send the order, I will have two weeks to polish my software. (Or get distracted by other projects.)

kicad_logo_smallWhat I need to do to start this process is to translate my breadboard circuit design into something OSH Park can fabricate. This also used to be a huge barrier: industrial-level circuit board design software carried industrial-level price tags. Fortunately there’s a free open-source option in KiCad, whose development received a significant boost from CERN. It’s still considered beta software in active development but the current builds are good enough for me to get started.

It’s time to learn KiCad!