We'll need to cut into our skull to access the hollow insides, where we'll be placing the HalloWing, battery, PIR sensor, and the wiring.

Cutting away the eye sockets will allow the eyeball and PIR sensor to "see" what's happening.

Want to print your own skull? Here's a 3D model by Thingiverse user ccombs that he built to fit the HalloWing! https://www.thingiverse.com/thing:3153240

Cut Open the Skull

You may want to remove the jaw first if your skull has one, just to make it easier to handle.


Next, carefully use a hobby knife to cut open the back of the skull as shown.

There are many ways to secure the lens. A laser cut holder is very precise, but you can also use zip ties as shown below! Or, try a 3D printed version https://www.thingiverse.com/thing:3152874

Attach the Lens -- Frame Method


Use four nylon M2.5 standoffs and eight screws to connect the lens to the HalloWing as shown, using an acrylic laser cut holder. You can use this file to laser cut your own from 2mm thick acrylic.


The lens will magnify the animation on the TFT as well as give the eye dimension when viewed at oblique angles.

Zip Tie Method

Feed thin zip ties through the holes at the bottom of the board, and then over the lens edges and back through the holes at the top.


Secure each end on the back side with a second zip tie like a fastener.


Trim the excess.

Cut Open the Eye Socket


Use a hobby knife to cut out the back of the skull's eye socket. Try to cut the hole about the same diameter as the lens.


You can touch up the spots where the lack of paint reveals white plastic with a marker.

Do a test fit to see that the lens will clear the hole, you can adjust if needed. It's OK if there is extra gap space, we'll hide it later with some felt or cardstock.



Second Socket

Repeat the process for the second socket which will hold the PIR sensor. Yes, it will look like a terrible, milky white dead eye.

Again, test fit the PIR sensor in the socket and adjust if needed. Don't worry about extra gap space around the sensor, will take care of this later with some felt (or cardstock).

PIR Sensor Prep


The PIR sensor has three connections for power and data. Plug them into the JST cable like this:


  • Red to +5V
  • White to Data
  • Black to Ground

Later, you can adjust the sensitivity of the PIR sensor (by turning the trimpot labeled "sensitivity adjust" in the image above) up to about 20' (6 meters) to tune it to the location you deploy the All-Seeing Skull.

To learn more about PIR sensors, take a look at our guide here!

Plug the PIR sensor into the SENSE port on the HalloWing. If you're using a battery you can plug that in as well.

Custom Fit with Felt

Depending on the size and shape of the skull and socket, you may want to customize the fit a bit more. You can use some black felt or construction paper to mask some of the socket space.

Cut a small piece of black felt or cardstock to a rectangle a bit longer than the HalloWing, and roughly 3/4 of its width. This will be used to mask off the gap to one side of the socket, keeping the lens pressed against the inner socket ridge.


Mark and cut a half circle from the center of the felt, as shown, then fit the lens into it.


Mark and cut two small holes positioned over the screws and then affix the felt to the board using the screws.

Insert Eye


Now you can insert and secure the eye lens and HalloWing in place inside the skull.


Now the felt nicely blocks the gap!


You can use a couple of dabs of hot glue on the felt and at the base of the HalloWing to secure them in place inside the skull.


Insert PIR Sensor


You can use the same method with some felt for the PIR sensor, as shown here.

The skull assembly is complete, next we'll program the HalloWing.

This guide was first published on Sep 07, 2018. It was last updated on Jun 12, 2024.

This page (Build the All-Seeing Skull) was last updated on Mar 08, 2024.

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