[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?