Energy-Harvesting Electronic Holiday Card 2024

Energy-Harvesting Electronic Holiday Card 2024

Hello friends and family, and happy holidays!

We’re delighted to share our electronic creation with you this holiday season, six long years after the previous one. The theme this time around is “powered by the holiday spirit”, and it’s an exercise in energy harvesting.

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Overview

What is this? Well, it’s an electronic (as in, circuit board and microcontroller) holiday card that harvests energy from ambient radio waves and light (though not with a traditional solar panel) and flashes fun LEDs using that harvested energy. All with no battery!

In addition, it features a clever mode by which it can be remotely controlled from your WiFi-enabled phone — without actually joining (or providing) any WiFi network.

Photo of the card you received in the mail

Want to know how to use it? Check out the instructions.

Curious about how it works? Or just want to see pictures of prototypes and renderings of antenna simulations? Lots of detailed technical info for you to digest!

There are at least three distinct ways to provide power to the card. Can you find them all? For example, you can power the card using the radio frequency (RF) energy your microwave oven naturally leaks while warming food:

The card doesn’t have a battery to wear out (that little round silver thing is a capacitor, not a battery), so don’t be afraid to play with the card as much as you’d like.

To get this all to work, the card’s design makes power efficiency paramount. Depending on the mode of operation, the card will run on as little as an average of just 400 nanowatts (billionths of a watt)! More details are on the technical info page.

Even in its highest power modes, it averages only tens of microwatts (millionths of a watt) of power consumption, and in its “normal” mode while running continuously it draws about 16 microwatts. (For comparison, a quartz wristwatch draws about 5 microwatts, and a coffee pot draws about 100,000,000 times more power while brewing coffee.)

Once you figure out how to power the card, try controlling it remotely! All you need for that is a phone that’s connected to a 2.4 GHz WiFi network. (It’s a bit of a magic trick — For the technically minded among you, see if you can figure out how the card manages to do that.)

With warmth and love,

Jeff Keacher, Sean Beever, and Sophie

December 2024

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