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 71ÂºC. Even as this marvelous beverage fills your room-temperature cup, temps can still reach a blistering 58ÂºC. Finally, after a couple of minutes cooling, your coffee is safe to drink, at a lukewarm 47ÂºC.
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.