This Battery-Free LED Coaster Is Charged Wirelessly

LEDs are a great way to brighten up your decor, and it’s usually pretty easy to add a strip of LEDs just about anywhere in your home. One fun and inexpensive way to do that is with LED coasters, and you get the added bonus of ensuring that your house guests can’t miss them. Most LED coasters — both commercial and DIY — use a battery to provide power. But what if you could build an LED coaster without batteries or a power cable? That’s exactly what Scott Clandinin has done with this wireless and battery-free LED coaster.

At first glance, this looks like any other LED coaster with a ring of green surface-mount LEDs running around the circumference of the PCB. Each LED lights up in sequence, creating a simple but elegant spinning effect. But that’s where the similarities to typical LED coasters end. The operation of LEDs is controlled with basic IC components instead of a microcontroller to save power. Those include a 555 timer, 4-bit binary counter, and a 4–16 bit decoder. By omitting a microcontroller and only lighting one LED at a time, the total current draw is kept to an absolute minimum.

It’s important that the power consumption be low, because this coaster doesn’t use any batteries. Instead, all of the energy is stored in slim-profile supercapacitors. Those are charged by a wireless coil that receives power from a separate charging base. The supercapacitors don’t store a lot of energy, but they have enough to keep the LEDs blinking for roughly four hours. Because no charging or power cables are needed, Clandinin was able to completely seal the coaster. He did that by placing the PCB in a 3D-printed dish, and then pouring art casting resin over the top. Heating up the resin with a lighter as it hardened kept bubbles from forming inside, resulting in a classy and seam-free appearance.