Introduction: Smart Coaster

Apparently I am a "nekojita," (Japanese for a person who can't handle hot food). Cats don't like high temperature food (they say), so a person who doesn't fancy molten bits in their mouth is called nekojita (cat tongue).

With a learning sensor from Aniomagic, I built a smart coaster that can monitor the temperature of my drink: green means it's just right, red means it's way too hot, and white means I'll need to heat it up again.

Video here:
(or here )

The wonderful thing about the learning sensor is that I don't have to hook it up to a computer to reprogram it. If I wanted to monitor (say) a cold drink, I can recalibrate it by tilting the coaster, which activates the tilt switch.

The coaster goes to sleep after 30 minutes, and wakes up when picked up. (next: a version powered by heat from the drink)

Disclaimer: We make and sell some of the materials on our website.

Step 1: Ingredients

- a temperature learning sensor from
- red surface mount LED (digikey part# 67-1695-1-ND)
- green surface mount LED (digikey part# 67-1357-2-ND)
- white surface mount LED (digikey part# 160-1737-1-ND)
- tilt switch (mouser part# 107-2006-EV)
- large battery (CR2032)
- plastic battery holder

You'll also need
- some acrylic (or something similar)
- a soldering iron
- wire-wrap wire
- a laser cutter (lucky us :-)

Step 2: Design & Preparation

First, figure out where you want the lights, and your desired disc diameter. I used my favourite cup as a guide.

To embed the LEDs into the underside of the acrylic, measure and etch three rectangular bevels. There are three more on the other side in case the future me wants indicators there too. Drill holes for the learning sensor too.

Next, cut out three doughnuts that will be stacked up to clear the battery holder.

Some LEDs don't have indicators to tell which end is which. Connect a 3V battery to each one, and mark the minus... it makes things much easier.

Prepare the wires by stripping and tinning them. The exposed wires are very short so they'll be flush when soldered into the learning sensor. "H", "M", and "L" go to the red, green, and white LEDs respectively.

Step 3: Soldering Wires

Solder on the wires: I used white for "+", black for "-", purple for "calibrate," and so on.
Pass the wires through the holes until the sensor is flush.

Since the solder connections are fragile, apply some epoxy and fill in the holes (you don't want to resolder through acrylic if any break). Glue down the LEDs as well.

This is also a good time to glue down the battery holder... use one of the doughnuts as a guide. Make sure you'll have clearance for replacing the battery.

For multi-drop connections like ground, I prefer to expose a long arc of wire and connect with smaller pieces as needed.

Hook up all the "-" of the LEDs to the negative terminal of the battery holder.

Step 4: Stripping Wires by Melting Insulator (tip)

Here's a tip: when you want an exact length for wire, you might run into trouble with the regular wire stripper, as you may stretch or even cut the wire by accident.

In these cases, I like to burn off and trim the plastic with the soldering iron because there's no risk of breaking.

Step 5: Attaching the Ilt Switch, Gluing the Body

After wiring the tilt switch, angle it so that it will be off when the coaster is flat on the table. 30 degrees should do it. Glue it in place.

Stack the disc and doughnuts, and glue them together. You can use more exotic acrylic glues, but since this isn't load bearing, a thick epoxy will do.

Step 6: It Works! Turn on and Calibrate

When the smart coaster is turned on for the first time, any of the lights may be randomly lit, depending on the temperature.

Fill a cup with the "right-temperature" beverage of your choice and let it sit on the coaster for a minute. Remove the cup and tilt the smart coaster so all three lights start flashing - this recalibrates the sensor.



Akin Yildiz (author)2014-12-05

hello aniomagic,


I am working on a plant pot that changes color when different conditions are in place. since the battery life is a huge issue, we have to use just one rgb led. i've never worked with acrylic like this before and would love to hear your opinion.. I am assuming that there will be an outside layer on the plant pot of thin sheet of acrylic and the light will be hidden closer to the bottom of the pot? here is another instructable that is similar in idea;


I also am planning on a wireless charging system. I was just able to upgrade it with a wifi module. now the pot can e-mail you once a sensor is triggered, and also saves the collected data on the cloud. you should consider using the ESP8266 wifi module;


i am trying to assemble a team of amazing people. we are a non-profit, open source electronics company, specializing in plant care instruments - feel free to message me with any questions. all contributors are listed with their input/date on our webpage.

thank you very much for such a detailed instructable !!! it's amazing how you don't need a computer in there to re-program.

plant pot.pngUntitled.jpg03.jpg
Wasagi (author)2010-12-18

Neat! five stars!

ReCreate (author)2009-05-12

Now one for plates,I rarely drink anything above 70 degrees. But i do,However,Eat Food above 70 degrees. There should be like a probe,You stab it into your food,In this case,Lasagna,And it tells you if it is too cold,getting cold,Or too Hot. That would Solve all of my burned tongues.

DemonDomen (author)ReCreate2009-06-08

Maybe I'll do something like that. Just need to find a nice box to put it in.

ReCreate (author)DemonDomen2009-06-08

Project Box, Maybe a 9V battery Casing?

aniomagic (author)ReCreate2009-05-12

That happens to me too! Especially pasta with fillings like raviolli... happens more often than I'd like. I'm thinking like the meat thermometers...

ReCreate (author)aniomagic2009-05-12

Raviolli? I don't think they heat that up too much,but what about something for pizzas,Like a little sheet you put under it to tell if it is(Warm,cold,hot,lava)Ish,That would Solve all the tomato sauce and cheese stains on the floor

aniomagic (author)ReCreate2009-05-12

I think this would also work great. You'd probably need several sensors on a large sheet: "the pizza slice on the top left is still too hot... try the one on the right" :-) Now if only it didn't need a battery, I'd be all set. There might already be an easier way to do this with thermachromic paints or something...

ReCreate (author)aniomagic2009-05-13

Thermal Thingies? They generate electricity when exposed to heat

erosser (author)2009-05-12

It would be awesome to have this built into a traveling mug--I always burn my mouth because the only way of really testing it is drinking out of that little hole... Perhaps putting a probe in-between the outer insulation and the inner cup? Very nice work, and extremely sleek! Looks like Apple should sell it...;) A constructive suggestion: captions on the pictures that tell what's going on would be very helpful.

aniomagic (author)erosser2009-05-12

I agree! It might be sufficient to put the sensor in the cap itself, close to the hole. This assumes that the temperature in the air in the flask would correspond closely enough with the liquid temperature... Thanks for your comments and suggestions.

Bongmaster (author)2009-05-12

nice idea :)

Berserk87 (author)2009-05-11

nice guide. i planned on making something like this eventually, but have been toying with other projects.

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