Ever since I was 8, I’ve loved Harry Potter and the world that J.K. Rowling built with her books. I always related to Harry’s friend in the book, Ron Weasley, and I especially loved that Rowling tied the wizarding world into the real world.

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I wanted to bring a piece of that world into my own (while also geeking out with Raspberry Pi and GPS), which led me to re-create this famous prop from the book. This project is an Internet of Things Location Clock (or Whereabouts Clock, or Weasley Clock). Rather than having two hands that give you the time of day, this clock has a hand for each member of your family or group, and moves the hand to point to wherever that person is in the real world! My clock, for example, has two hands (for my wife and me) and shows locations for Home, School, my Parents’ house, our favorite bar, the opera house (we volunteer there), etc.

The Location Clock runs on a Raspberry Pi mini computer, which subscribes to an MQTT broker — a server for routing messages in the MQTT internet protocol. Our phones send a message to the broker anytime we cross into or out of GPS waypoints we’ve set up in the OwnTracks phone app, which then triggers the Pi to run a servo that moves the clock hand to show our location. And the Node-RED programming tool made it easy to automate without writing any code.

I’ve seen a couple different approaches to this clock idea, but I especially valued those of Allie Fauer, and Alya Amarsy. Here’s how I made mine.