Zelda Guardian security camera

By Rosie Hattersley. Posted

When it comes to life goals, Oxford master’s graduate Naomi Pentrel is doing pretty well. Along with an impressive roster of academic achievements and professional roles as a software engineer at the likes of Google, Microsoft, and Bloomberg, she is a regular public speaker, enthusing about MongoDB and other database possibilities. The savvy coder has a very important housemate to keep her in check: the toy poodle, Ernie, who she and her partner took under their wing two years ago. Although the Netherlands-based couple largely work from home, when they’re away they like to check in on their beloved Ernie: hence creating a Raspberry Pi 4-based Zelda Guardian so they can see what he’s up to. Aw, cute!

What a character!

Although Naomi and her partner can’t bear to be parted from their poodle, when they are they generally set up an old phone through which they can watch him. However, “our living room is connected to a kitchen and there is no way to set up a phone camera to capture the entire room. If Ernie moves out of view of the camera, we can’t see him,” she explains.

Not long before the latest version of The Legend of Zelda launched, Naomi found herself looking at a picture of a guardian robot – an eight-legged machine that can be either stationary or able to move about. In the game, these guardians can rotate their heads and attack you with a laser. Obviously, it was only the former aspect that Naomi wanted to copy.

Naomi spent hours painting the details to give the Guardian webcam an authentic Zelda feel

Naomi decided to 3D-print a Guardian model and place a camera where the laser is. She would mount the Guardian head on a servo, connect everything to Raspberry Pi, and create a functional Zelda Guardian to monitor her dog.

Naomi’s first Raspberry Pi project, back in her student days, paired a Raspberry Pi with a camera to create a web-based security system, so she knew what to expect when planning this setup. Decorating the Zelda Guardian would be the real challenge and a great creative outlet. To add to the challenge, Naomi also decided to run Viam software on Raspberry Pi, and use a TensorFlow Lite machine learning model to detect her dog and program the Guardian to rotate the head to follow him around the room.

Raspberry Pi seemed a good choice since “it’s powerful enough to run the machine learning model I needed, and it was easy to get a ribbon camera for it.”

Team effort

“Luckily, I am not the first one to have the idea to build a Zelda Guardian and there was already a brilliant Guardian 3D model on Thingiverse with space for LEDs and a servo,” says Naomi. She chose a different Guardian head.

Naomi asked her friend Hugh Rawlinson to help with the 3D printing using a filament that allows the light to shine through. Naomi then painted the parts that shouldn’t let any light through.

The Zelda Guardian camera successfully recognises Ernie

Next, came the dual challenges of fitting components such as Raspberry Pi 4 and ensuring the camera stayed inside the head. Hugh helped her tweak the Guardian head’s design to include mount holes so she could attach a ribbon to a Raspberry Pi Camera Module v1.3. “Because they’d used the ribbon cable, the head couldn’t spin freely. However, for the space I wanted the Guardian for, 180 degrees of movement is enough, so I used a 180-degree servo,” explains Naomi.

Raspberry Pi itself needed some form of box to keep it upright inside the Guardian’s head. She hit on the idea of slotting it inside a tranche of tree trunk, and was able to recruit her partner to assist with the woodwork, cutting into the tree slice and giving the Guardian a beautiful base. Naomi then put it all together and painted it to look like the real thing.

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