Walk into the room and the skull on the shelf wakes up. Its eyes glow green. As you cross the room, its head turns to follow you. Step closer and the eyes shift towards red. Stand still and it keeps staring… until, after about thirty seconds, it loses interest and drifts back to sleep, its eyes slowly pulsing.
Pick it up and look inside. There is no camera, and no PIR motion sensor either.
So how does it know where you are?
I will get to that. It is the best part, and I am saving it. This is my Halloween build for 2026, and it is also my first real step into animatronics: making a machine that doesn’t just move, but behaves.
Can’t wait? The whole build is already out for my channel members. All three videos are available to them today, weeks before they go public. More on that below.
Three layers: eyes, movement, brain
I split the build into three parts, and each one is a video:
- The eyes show the skull’s mood (this post).
- The movement is where the skull stops moving like a robot and starts moving like a predator.
- The brain is how an empty plastic skull finds you, chooses who to stare at, and decides when to get bored.
Everything is off the shelf and cheap. The brain is a Waveshare RP2040-Zero, although a Raspberry Pi Pico or Pico 2 on a breadboard works just as well. The skull came from a discount supermarket, full of sweets. The sweets did not survive the build.
Why I built the eyes first
Everything else hangs off the eyes. Movement makes the skull feel alive, but the eyes make it feel like it is thinking.
Each eye is a WS2812B LED disc with seven LEDs: one in the middle for the pupil, and six around the edge for the iris. The two discs are chained together, so a single GPIO pin (GP10) drives all 14 LEDs.
The eyes are not just decoration. They are the skull’s display:
- Iris colour shows distance. Green when you are far away, shifting to red as you get closer.
- Lit iris LEDs show how many people it can see. One LED per person, chasing round in opposite directions in each eye.
- A pulsing pupil means it is asleep.
So before the skull moves a millimetre, you can already read its mind.
Three details that make it reliable
These took the build from “works on the bench” to “works all evening”:
- A logic level shifter. The RP2040 outputs 3.3 V signals, and these LEDs expect 5 V. Sometimes you can get away without one. At a Halloween party you don’t want “sometimes”.
A 1000 µF capacitor across the 5 V supply. Switching 14 LEDs from off to full white in one go pulls a sudden surge of current. Without the capacitor, the supply dips and the microcontroller browns out and resets, usually just as someone walks past.
Capped brightness. It looks better through the skull’s plastic, and your power supply will thank you.
On the software side I use the excellent PicoLED library by Forsaken NGS. I have used it on everything from LED rings to lightsabers. I split the 14-LED strip into two slices, one per eye, and wrap each in a small Eye class that handles the pupil fade and the iris animations (static, clockwise or anticlockwise). The main loop just keeps “ticking” the eyes so the animation never stalls.
The full code, wiring and parts list are on GitHub: github.com/DrJonEA/SkullHead2026.
Watch Part 1
This Skull Watches You – Glowing LED Eyes Halloween Build Part 1 goes public on 1 October:
youtu.be/QYEaLgX0qEk
Coming next: how does it hunt you?
In the next post I will show how the skull moves. Out of the box, servos move like robots: full speed, then a dead stop. My skull has two ways of moving. One is gentle, almost human, for when it is waking up or turning to look at you. The other is a sudden predator strike, for when it is hunting you across the room. The difference is one small technique, and it is the key to every animatronic I have planned.
Then comes the brain: what is really inside that empty skull, and how it decides who to stare at.
Watch it all now
Parts 2 and 3 go public on 8 and 15 October. Channel members can watch all three today.
Members get every video the day I upload it, instead of waiting for the public release. Right now that means the whole skull trilogy, plus four more videos that won’t go public until late October and November:
- ThingsBoard HTTP vs MQTT: which is better for low power?
- I got the Pico 2 W down to 3.5 mA, then the SDK broke it
- EMQX + HAProxy + Ansible: the IoT stack behind my Pico W display
- I built an LED badge in 2 hours on an RP2350 matrix
There are two tiers, Tinkerer and Technologist. Both get the early access. Technologist is for anyone who wants to back the channel a little more, and it comes with more chances to talk with me directly. Every membership also helps me get the droids to Open Sauce in San Francisco.
Join the channel here, and find out what is inside the skull before everyone else.
Some links (Waveshare) are affiliate links. They cost you nothing extra and help keep the channel running. Nothing in this build was sponsored.