I have just published Chapter 7 of Volume 2 of KiCad Like a Pro, 5th edition. If you have already bought into the beta, it is in your account now. If you have not, there is a free excerpt at the bottom of this post.
This is the warm-up project for the volume: a 4×8×8 LED matrix array, which is 256 individually addressable LEDs in a single display band 80 mm wide, driven by four MAX7219s and an Arduino Nano. That is enough to scroll a message, draw a bar graph, or count something down in characters you can read across a room.
The board
If you know the clock from the 4th edition, this is its modernised descendant. It keeps the display, the two buttons and the power switch, and it adds three things. Power now comes in over a USB-C receptacle rather than through the Nano. A P-channel MOSFET load switch sits between that receptacle
and the board, so the little slide switch never has to carry the 1.3 A the display can pull, which is more than four times what its contacts are rated for. And the outline is simpler, so the finished board drops into a project box without a fight.
The gadget it becomes is a Pomodoro-style countdown timer. Counting down a known number of minutes needs no absolute time reference, so there is no real-time clock on the board and nothing on it has to know what day it is. If you want one that does, the chapter shows you the neat route, which is not to add an RTC chip but to swap the Nano for a WiFi-capable module in the same footprint and let it fetch
the time from the network.
Why a warm-up project at all
Volume 2’s capstone asks you to author your own parts. Before that, I wanted a project that teaches
something almost as valuable: how to stop doing the same work four times.
The board is really one cell repeated. Each cell is a matrix, its driver, a current-setting resistor and a decoupling pair, and the only difference between the four copies is their reference designators. So you draw one cell, capture it as a design block, and stamp out the other three. Then, on the board, you place and route that single cell and let KiCad copy the placement and the routing onto the other three at exactly the right pitch. You lay out a thirty-two part board carrying 256 LEDs, and of its four identical cells you place one and route one. A tool does the rest.
That is the difference the chapter sets out to show, and it is the same difference whether a board repeats itself four times or forty.
What the chapter covers
- Design blocks, which are the main new skill, and which return in Chapter 9’s four-motor extension on a bigger board.
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Multi-channel design and “Repeat Layout”, so three of the four cells are placed and routed without you drawing a track, and so a later change to one cell is pushed to the others rather than
edited four times over. - Precision positioning, which is what makes four panels read as one display. I use precise coordinates for the positioning, instead of “eyeballing” it.
- Net classes with their graphic columns filled in, so the power rails stand out on screen by colour and weight, plus an assignment pattern that matches more than thirty nets at once.
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A power budget worked before anything is drawn. A multiplexed display does not draw its average. At any instant one row is lit and can pull 320 mA through a single driver, in hard bursts,
so that is what the copper is sized for, not the 5 mA per LED that the duty cycle suggests. -
Reading violations rather than counting them, in both the ERC and the DRC. A violation that
describes something you have not done yet is information, not an error.
Creating a single screen
The matrix pins sit on a 2.5 mm pitch. The Arduino Nano sits on 2.54 mm. The 100 mil grid you have used since Chapter 3 moves a part in whole steps of 2.54 mm, and no number of those steps adds up to the 20.0 mm the matrices have to sit apart. Eight steps come to 20.32 mm, so each join opens by 0.32 mm, and across four panels the display band comes out 80.96 mm wide instead of 80.0 mm.
It is just a display that reads as four panels placed near each other rather than as a single screen. The fix is to match the grid to the job, work the board in millimetres, and type the positions of the four matrices rather than nudging them onto any grid at all.
Read the excerpt
The chapter opening is free to read, no purchase and no email required: the 4×8×8 LED matrix array excerpt. It covers the board, the sketch it started as, and the five skills the project builds.
What I am writing next
Chapter 8 is the capstone project of Volume 2. It’s an original dual H-bridge motor driver built around the DRV8833, where you author the parts yourself rather than pulling them from a library. Chapter 9 is an optional extension that puts a second DRV8833 on the board for four-motor control, and it is where the reuse habit from this LED matrix project pays off a second time. Both are in drafting now, and both will appear in your account as they are finished.
The early adopter option
I am writing this book in the open rather than disappearing for a year and handing you a finished object. You can buy in now, read each volume as it is drafted, watch the thing take shape, and tell me what is working and what is not. Your support funds the writing, and your feedback can change what I write.
Two things come with buying early.
The first is access. One purchase covers the whole series: Volume 1, which is complete, Volume 2 as I finish it, and Volumes 3 and 4 as they arrive, plus every revision and correction for the life of the 5th edition. New chapters appear in your account as they are written, which is how Chapter 7 reached its readers this week. You also get access to the book’s community space at the Community Tier level, and you keep that for good, even after the book is fully published. That space is where I post each release and where readers tell me what needs fixing.
The second is price. The book costs more as it becomes more complete, and it rises each time a volume is finished. It started at €20, it is €30 today with Volume 1 complete and Volume 2 well along, and it ends at €50 when all four volumes are done. Whatever you pay is locked from the moment you buy, and I will never ask you for the difference however much the book grows from here. Buying today is simply the cheapest this book will ever be.
On the flip side, you are reading a book in motion. Chapters get rewritten, sections move, and a paragraph you read in today may look different in a month from now, usually because a reader told me it was not clear enough. So I mark what is still being written, and you see that marker before you open the chapter. You also don’t get a downloadable PDF until the full book is written and stable.
If that sounds like a good deal for you, head to techexplorations.com/kicad to read more, check exactly where each volume stands on the status page, and take the early-adopter price while it is still €30. I would like to hear what you make of the LED matrix, and whether your four panels line up as neatly as mine did.