This is a lovely little SAO I made for Hackaday Supercon 2025. I've been really into print making lately, so the idea was to somehow combine analog electronics and print making.
This is the full write up - so let's go through the whole process!
I knew I wanted something with two sections, and I wanted the lights to be flashing somehow, so that there would be someway to work in a cool analog circuit. All I needed was the design!
I was a little intimidated by drawing it myself at first - I'm not a great visual artist, but I took the same approach as building anything, just keep prototyping. I probably drew and re-drew something about a dozen times before I settled on a little sketch that I liked (the image on the left).
Once I had a drawing I liked I needed to come up with a circuit, and fast! The deadline getting boards made before Supercon was fast approaching. I settled on something simple - the cat would remain lit constantly, and the stars would fade in and out. The constantly lit LEDs are easy, the others...
To get the LEDs to fade in and out I used a simple oscillator circuit - it's a pretty simple circuit you'll find if you Google "simple oscillating circuit". The output of this circuit is then fed into an RC filter to turn it into a triangle wave, the triangle wave is then converted to a current using Q3, which has been biased with R8 to get the correct amount of on/off time. That current is then amplified using Q4. The current through the LEDs can be tuned by R7, which is there to make sure we don't blow them up!
You may be wondering - why has he stacked 3 diodes in series? That is to approximate a white LED, because white LEDs have a significantly higher drop across them than a regular diode, I guessed equal to about 3 regular diodes in LTSpice though in hindsight it was probably more like 4.
Before diving into boards I wanted to make sure everything worked, so I made a little prototype! It used a board I had previously made with a bunch of white LEDs in parallel, and a handful of discrete components.
Simulators are good - but this really helped get all the bias points just right for the look I wanted. I also was able to use it when prototyping my block print to make sure I would get the effect I was after, and to select what kind of paper would be best.
Once I was sure everything would probably work - I drew up the boards in KiCAD and designed a little frame for everything to go into, as well as the divider to help keep the two light zones separate. Then all I had to do was 3D print a lot of little frames while I waited for the boards to come in.
To make sure everything fit together just right I exported the board from KiCAD as a 3D model - this is an awesome feature! Strongly recommend it if you don't use it already.
Once I had all the electronics and 3D printing done I had to finally sit down and carve the block.
Luckily, carving the block wasn't too bad. The real challenge was finding the right ink! I tried intaglio ink first because that's what I had (turns out you can't use intaglio ink as block printing ink, or at least I couldn't). After that fail I eventually settled on a craft store ink pad, it was definitely way easier than messing with the roller for every little stamp. I think I could have gotten a neater result with a more traditional block printing process, but I kind of like the inconsistencies the ink pad caused, and I really liked not having to ink up my block with a roller every time.
Once the boards came in, the 3D printer finished up, and I finished making all my little block prints - it was time to put everything together!
Everything fell into place reasonably well, and it was all glued together with UV glue (my new favourite way to glue things).
Hopefully that all made sense - if anyone tries their own block printed SAOs please let me know! Everything I could upload I did - you can find all the design files on my github. I am unfortunately not able to share much with the block print itself, because I did all the design work with pen, paper, and a linoleum block, so I guess if you want to make one you'll just have to come up with your own print!