HOW TO – Make a “Smart Coaster”

HOW TO – Make a “Smart Coaster”

Smart Coaster
Never burn your mouth on a hot drink again

No matter your poison — coffee, tea, hot chocolate, sake — take a gulp too soon out of the pot and chances are good that you’ll burn your mouth. But build this Smart Coaster and you’ll always know when it’s safe to sip.

According to my thermometer, common coffee brewers produce a cup of perfect coffee that is positively molten to the tongue, at 71ºC. Even as this marvelous beverage fills your room-temperature cup, temps can still reach a blistering 58ºC. Finally, after a couple of minutes cooling, your coffee is safe to drink, at a lukewarm 47ºC.

A simple circuit consisting of a thermistor, a special low-power operational amplifier (op amp) IC, an LED, and a couple of passive components will enable us to safely monitor the temperature of our coffee cup. Bundle this circuit inside a round metal container (metal helps conduct the cup’s heat to the circuit) and you have a Smart Coaster.

18 thoughts on “HOW TO – Make a “Smart Coaster”

  1. Tercero says:

    Reads like I’m whiny, but, it’s state “follow the schematic” on the PopSci page. I can’t find a link to the schematic. Am I missing something?

  2. Pavel Ushakov says:

    That’s a very good idea. Don’t you hate when your mouth burns :)

  3. Simon says:

    Living in NZ it always amuses me that Kiwi boot polish is in fact Australian! Using the tin as a housing is a neat idea.

  4. Luke Warm says:

    I’ve just measured my coffee, and the machine spits it out at a blistering 94 degrees Celsius. That’s too hot to drink, but I start drinking it at 70 degrees or slightly above.

    When it gets under 60 degrees it is already slightly too “cold” to enjoy.

    Is this a regional thing? I think my temps are pretty normal in Europe.

  5. Anonymous says:

    I also had trouble finding the schematic. I’m guessing it’s in the magazine and not included on the site. Too bad, looks like a cool project.

  6. Tercero says:

    And it appears a bit pointless to post and article about a build…without all of the necessary information. I like popSci, but the article (and link) is like a lost leader in the local papers that advertises .99 electronics, only to find they’re out of stock but “expect some in the next couple of weeks”.

  7. Thinkerer says:

    Measuring the temperature of the bottom of the mug adds another complication — the thermal conductivity of the mug material will affect the final value to the point that a dewar flask (Thermos) type mug would be mostly useless.

  8. Sean Michael Ragan says:

    Or you could just try using a cup without a handle: If it’s too hot to pick up, it’s too hot to drink.

  9. The Oracle says:

    I’ve got to wonder about those temperatures too. I drink my coffee in the 70’s as well. Below 50, it’s too cold to enjoy.

    Out of curiousity, do you chug your coffee? At those high temperatures, you take small sips and savour the coffee, the heat makes the flavour and aroma pop into your senses and with a tiny amount you get a little spike of heat that doesn’t have enough thermal energy to burn you, your mouth cools it down long before it gets burnt.

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