Temperature sensing mug means never burning your mouth again

temp_sensing_mug

Some people tend to get awfully attached to their favorite mug. Like an old friend, the mug holds a special place in their hearts, and there’s a weird sadness when it finally gives up the ghost. Through the winter months [Ben’s] girlfriend is never without hers, and when it broke, he decided to give her a new one with some added functionality.

He built her a temperature sensing mug that uses a rather novel way of determining how hot or cold the contents are. Instead of using a thermistor to determine the drink’s temperature, he opted to use a simple diode since it is well known that a diode’s forward voltage varies with temperature. After determining the diode’s voltage range using hot and cold beverages, he hooked it up to the ADC of a PIC12F615 micro controller. The temperature is displayed via 10 LEDs, which are driven through a pair of 8-bit shift registers and buffers since his PIC did not have enough pins to control them on its own.

He had some PCBs made, and after a handful of setbacks got everything put together. He says the mug works pretty well, though the display changes a bit more slowly than he would like. He also mentions that if he builds a second version, he will be sure to select a different PIC that has enough I/O pins to do the job, as well as use a thermistor instead of a simple diode for sensing the temperature.

Continue reading to see a brief demo video [Ben] put together.

Comments

  1. Life2Death says:

    Why not a single RGB led?

  2. Mccoywm says:

    Cool project, but I would like to see a single RGB led that goes from blue to red with temperature.

  3. mixikaabin says:

    or a dual led, so you can have different colors. one for when is hot, and one when it is cold. Then when it is just right the both light up :D

  4. Fallen says:

    I like the bar graph…but a single bi colour LED and a 8 pin SOIC would greatly miniaturize this circuit.

  5. Swankie says:

    theres no such thing as too cold, mixi

  6. Johannes says:

    Cool mug! Horrible vid!

  7. bolle says:

    That’s one giant mug!

  8. pookey says:

    This is cool, and a neat home-brew project,

    If I were to manufacture temperature-reporting mugs, however, I would base my product on color-changing crystals molded into plastic (to protect them from dish-washing. ) This is a simpler approach to the same end, and doesn’t require a power source.

    The crystals I’m talking about form the basis for “mood” rings, and those flat, stick-on thermometers you can sometimes find at the dollar store.

  9. HackerK says:

    @Mccoywm yup agree. a single RGB (or even RG bi color LED) with PWM.

    Bar LED does look cool if he can program some animation to move once in a while ;)

  10. Adrian says:

    Whats wrong with using a shift buffer? Its not like you need to update particularly fast, is there something I am missing?

  11. Brennan says:

    The temperature range is very limited – only 30 ADC codes. But I suppose it doesn’t need to be more unless you wanted to display the actual temperature. Like everyone else said, this should have been done with a single RGB LED and PWM output. Fade hot colors to cool colors as the coffee cools.

    I want to do something like this but have it be a board that sits on the top of the mug and indicates when the coffee is cool enough not to burn your tongue. I was thinking of using an IR temp sensor, however overkill that may be. I don’t like how adding it to the base of the mug restricts you to using only that mug. But that’s just personal preference.

  12. trialex says:

    I wonder if hot coffee has enough temperature differential to generate power through a peltier element?

    A cup of coffee can run a Stirling engine, but that might be a bit unwieldy for this :-)

  13. CG says:

    The temperature sensor should be at the top of the cup so that it senses how hot the liquid you are about to drink is.

  14. Tony says:

    @pookey, mood rings generally have a pretty small temperature range. You can get stickers to attach to things that work the same way, but their range is small-ish as well. Often they’re made for a specific purpose, babies bath water, fish tanks, home brew kegs etc, and only work at the required temperature.

    He didn’t actually need the diode, the watchdog timer in the PIC is temperature sensitive as well (based on a RC circuit). Each chip is slightly different though, so calibration is needed to make it work for _your_ chip.

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