Pressure Plate LED Coasters!

Looking to use up some more of his flexible LED strip, Hackaday alum and Tindie writer [Jeremy Cook] tried for a funky accent to his dinner or coffee table: light up coasters.

Using his CNC router to carve out two pieces of translucent plastic to house four 3V CR2032 batteries, four pieces of LED strip, and some wire, [Cook] had created a pressure plate circuit that activated once a drink is set on it. The original layout of the circuit, however, didn’t work, and the space for the LED strips proved to be too small. A quick redesign and some more time with his router resulted in an almost working product. Initially intending to use screws to secure the coaster, hot glue provided the perfect amount of spring once he had thinned out the coaster top to allow it to more easily flex and complete the circuit.

Continue reading “Pressure Plate LED Coasters!”

Log coasters made with just two tools

diy-log-coaster-set

Still looking for that perfect gift? [Joel Witwer] shows us how to make a log coaster set and holder on the cheap. He figures he spent just $5 on the project and from what we can tell that all went to some polyurethane which he used to finish the wood pieces.

It started with an interesting-looking and appropriately sized log which he found on the side of the road. We’re not sure about the ins and outs of drying stock to ensure it won’t crack, but we hope he took that into account. With raw material in hand he headed over to the band saw. The cutting starts by squaring up both ends of the log while cutting it to the final length. He then cut the bottom off of the holder. What was left was set upright so that he could cut the core out of the log. This is the raw material from which each coaster is cut. A spindle sander was used to clean up all of the pieces. The last step before applying finish is to glue the bottom and sides of the holder back together.

[Joel] gave some tips in his Reddit thread. He says you should hold on tight while cutting out the slices for coasters because the round stock will want to spin. He also mentions that some of the slices aren’t as flat as they should have been, something to think about if you’re cutting these for yourself.

Color changing coaster has a built-in drink detector

[Robert] put together his own illuminated coasters that know when they hold a drink. They look fantastic, thanks to professionally produced PCBs and a layered, laser-cut acrylic case. They’re much like the pagers given to restaurant-goes who are waiting for tables, but this version is much fancier (and doesn’t include the vibrating/paging feature).

The RGB-LED board is a previous project which was developed using eight surface mount RGB LED modules around a circular board. It uses an ATmega168 paired with an MBI5168 constant-current LED sink driver. The coaster enclosure gave him room for a few more items, like the pair of AA batteries which work in conjunction with a boost converter to power the device. It also houses an IR reflectance sensor which is used to detect the presence of a drink on the coaster. This is important since an on-occupied coaster looks like it would be blindingly bright if there wasn’t a glass to diffuse the intensity of the LEDs.

He mentions that incandescent light bulbs mess with the IR reflectance sensor. But there must be some way to account for ambient conditions with the code, right?