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+# blobcat PCB
+
+![Yellow PCB standing, colorful LEDs in marquee mode. Printed on PCB:
+"TechJI 2023" and "owo :blobcat:"](img/blobcat-pcb/marquee.gif)
+
+▲ There are ten more LEDs on the back.
+
+Fun? Yes. Stupid? 100%. This is my second attempt at purely artistic PCBs
+(the first failed).
+
+TechJI is the organization I work in since 2021. I will retire from
+director this month, so I'm designing this as a farewell gift.
+
+Repo: [blobcat-pcb on Codeberg](https://codeberg.org/fkfd/blobcat-pcb)
+
+## Artistic design
+
+![Board outline](img/blobcat-pcb/outline.png)
+
+Board outline is based on [this svg of
+:blobcat_paw:](https://github.com/DuckOfDisorder/BlobCats/blob/main/SVGs/BlobCats/BlobCat_Paw.svg).
+
+I would have printed the pattern in black, if black silkscreen wasn't 10x
+more expensive.
+
+## Structural design
+
+You can snap the board in two and solder them up. The solder joints
+provide structural support and electrical conduction from batteries to
+circuitry. I took the idea from a project I saw earlier, but forgot which.
+
+## Logic design
+
+I <s>referenced</s> copied [FrostAutumn's design on LCSC
+OSHWHub](https://oshwhub.com/frostautumn/bie-zai-zhuo-li-fa-dian-v1-1).
+
+- NE555 in astable mode provides clock signal for CD4017
+- CD4017 outputs high level to exactly one LED
+- Each rising edge, a different LED turns on
+- Effect: marquee
+- Speed adjustable with RV1
+
+![Schematic for NE555 and CD4017](img/blobcat-pcb/logic.png)
+
+## Power design
+
+At first I wanted to use only one CR2032, just like FrostAutumn's design.
+Datasheet says NE555 needs 4.5V, so I'll need a boost converter. With the
+converter comes a lot of annoying stuff, like inductors, so I just said
+"fuck it" and threw away the converter idea.
+
+Now the board is powered by two CR2032s.
+
+## DIY Manual
+
+<details markdown="1">
+<summary markdown="1">__If you want to build your own, expand this__</summary>
+
+### BOM
+
+All R, C, and D are 0603.
+
+- U1: [NE555 SOIC-8](https://item.szlcsc.com/729488.html)
+- U2: [CD4017 SOP-16](https://item.szlcsc.com/331800.html)
+- R1: 2.2k (anything between 1k to 5k should work)
+- R2: 10k (or somewhere near that)
+- RV1: [500k](https://item.szlcsc.com/139843.html)
+- C1: 10nF
+- C2: 1uF
+- R10-19: 120 (120 to 180 is safe)
+- D10-19: LEDs, arbitrary colors, note that each reference is two LEDs
+- SW1: [SPDT, 6 pins](https://item.szlcsc.com/3178990.html)
+- BT1,2: No idea what the package is, I just happen to have some
+
+### Fabrication
+
+The fab may charge extra because they might mistake the battery board for
+a separate design. I negotiated out of paying for it.
+
+### Assembly
+
+When soldering, use flux generously.
+
+- Snap board into main board and battery board
+- File down the four snapped bits
+- Solder main board (the side with more parts first)
+- Solder battery board (make sure BT1,2 don't jiggle)
+- Rotate battery board by 90 degress
+- Insert into main board
+- solder 4 pairs of copper strips at crossing
+- Insert CR2032 batteries
+- Turn on SW1
+
+#### Note on LEDs
+
+LEDs typically have a green marking on the front side. It is the cathode.
+On the PCB, a U shape surrounds the LED. The valley is the cathode. It
+appears more yellow because it is connected to the ground plane.
+
+You should use the same color for each pair, because they share the same
+voltage. If you solder red and blue, only red will light up, because it
+requires less voltage.
+
+### Troubleshooting
+
+- It doesn't work at all
+
+Probe voltage across VCC and GND. If too low, check soldering on BT1,2 and
+SW1. Make sure BT1,2 lay completely flat and don't jiggle.
+
+If still no, check soldering on U1,2, C1,2, R1,2 and RV1. Gently nudge
+pins with tweezers. Does it jiggle? If so, rework.
+
+- An LED doesn't work
+
+First, check polarity.
+
+If the LED on the other side works, check if they're the same color. If
+you're not sure, replace.
+
+If neither LED works, check the resistor (R10-R19) and U2.
+
+### Bugs
+
+#### Battery
+
+CR2032 batteries exceed lowest board outline, assembly tips slightly.
+
+When using v0.4.2, solder BT1,2 (battery holders) a few millimeters above footprint.
+
+Fixed in v0.4.3.
+
+#### Filled zones
+
+Thermal reliefs work too well. When soldering BT1,2 and copper strips, you
+need to be patient. Heat will dissipate into filled zones. __Do not touch
+the board surface__; it will scald you. Use a clamp if possible.
+
+#### Important!
+
+Do not put blobcat v0.4.2 on a conductive surface. It will short BT1.
+
+</details>
+
+## Dangers of overcomplicating
+
+In earlier iterations, I massively overcomplicated the project by:
+
+- routing 20 pairs of LEDs instead of 10
+- driving LEDs with BJTs for fear of frying CD4017
+
+I managed to route them, but it was a pain. What's worse, I discarded the
+design, which technically marks my efforts moot. All this work for
+nothing.
+
+I don't know what the complexity of routing N parts is, but it definitely
+is higher than O(N).
+
+Don't overcomplicate your projects, kids!
+
+![Copper layers of overcomplicated design](img/blobcat-pcb/v0.2-cu.png)
+
+Copper layers in ▲ v0.2; ▼ v0.4
+
+![Copper layers of current design](img/blobcat-pcb/v0.4-cu.png)
diff --git a/docs/projects/img/blobcat-pcb/logic.png b/docs/projects/img/blobcat-pcb/logic.png
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diff --git a/docs/projects/img/blobcat-pcb/v0.2-cu.png b/docs/projects/img/blobcat-pcb/v0.2-cu.png
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diff --git a/docs/projects/img/blobcat-pcb/v0.4-cu.png b/docs/projects/img/blobcat-pcb/v0.4-cu.png
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 Projects below are sorted reverse chronologically (most recent first).
 
+## [blobcat PCB](blobcat-pcb)
+
+![Yellow PCB standing, colorful LEDs in marquee mode. Printed on PCB:
+"TechJI 2023" and "owo :blobcat:"](img/blobcat-pcb/marquee.gif)
+
+Fun? Yes. Stupid? 100%. It has no value other than blinky blinky.
+
 ## [Byseekel](byseekel)
 
 ![Both sides of a soldered PCB](img/byseekel/rev3.jpg)