Idea for this "mod" spawned from Bit-Tech's forum. People were talking about coaster that could have lights and ways of doing it. It didn't took more than 500ms when I imagined myself doing this based on GlowPad technique but with internal power source. No point on having coasters with power cords in my opinion. Anyway, here is a small tutorial that I wrote to show you how you can do these yourself. I made this prototype in around two hours so this alone proves that this mod isn't that hard to do. And one more thing; I don't try to encourage people to drink alcohol here. These coasters can be used with tee cups etc. as well.
How does it work?
So the basic idea behind this little invention is that the coaster will light up only when there is something sitting on top of it. You can use a regular on/off power switch if you just want to be able to turn the lights on when you are having a drink but I think that this coaster with "pressure sensor" is more high-tech. ;) This also allows the coaster to be water tight if wanted but it will make the replacement of the batteries bit harder.
CoasterGlow is made out of three layers. Top and bottom layers are made out of thin acrylic so they will bend when you apply a slight pressure against them. When the top part is pressed down by weight of the glass, + leg of that led will make contact with the battery, thus lighting the led up. That other leg is soldered to the battery and will make contact all the time. Most difficult part will be the trimming of those legs so that they will make contact when certain amount of pressure is applied but hopefully we manage to get it working.
To cut the discs I used a hole cutter meant for metals. I decided to get this over the regular hole saw because this way I don't have to get all these different sized bimetal hole saw blades to cut blowholes to computer cases. This one tool can handle all the regular fan sizes and everyting in between. To cut these acrylic discs the tool didn't work as smoothly as I hoped but still saved a lot of time compared if I had used Dremel for cutting.
I clamped down all the three layers at the same time so that I could make three discs with one cut. This method worked quite nicely even though the hole cutter tried to rip those 1 mm sheets to pieces. :)
Because I'm using the same basic idea that was used in BreezePad, the middle layer had to be hollow. This allows me to place all the electronics in between the top and the bottom discs. Again, to save time I used a column drill to cut out the centre piece from the middle disc. Only this outer ring is needed for this project.
To glue the top disc to the middle disc I used glass silicon. This allows a smooth joint so that the top disc can bend in more easily. As you can see from the image you weren't too careful about the amount if that silicon but because the inner circuitry will take so little space it doesn't matter.
Batteries for this mod had to be thin and I was lucky to find two 3 volt lithium batteries from my misc box. 3 volts is bit too high for the red leds that I used but because there will be two leds per one cell I decided to leave the resistors out. Because the middle disc is only 5 mm and I had 5mm leds I sanded them down a bit for a perfect fit.
I soldered the - legs of the leds to the battery. This way, when the + leg touches the + side of the battery, the led will be lit. I decided to leave all the + legs separated from each others but if you like, you can make one "central leg" that will light up all the leds at once.
hmm... perhaps too much hot glue? :) So, here are the + legs waiting to be pressed down against the surface of the battery. Be sure to trim the height of those legs and test if the leds light up properly when pressure is applied before you glue that bottom part in place.
Oh, and don't get confused about this top and bottom nonsense. It doesn't matter that much which side you call top and which side bottom. This coaster will work on both sides.
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