The CoffeeMeter was born in October 2001 when I had a spare Dallas Semiconductor (now Maxim) 1-Wire™ serial adapter (of the simple self-built App. note #74 type) which I decided to make useful by plugging it into my trusty old Linux box at work.
The actual thermometer sensor is a digital DS1820 chip which is periodically read by DigiTemp 1.6 software. The DS1820 is attached to an aluminum plate on which the object to be measured is placed and a Perl script updates the web page every time a change is noticed in the temperature.
The reason why the measurement is not done in realtime when the HTML page is requested – like any proper dynamic new media service should do – is that DS1820 has a really slow response time (max. 750 ms) which would make loading the page intolerably slow. It should be noted that the readings given by this setup are by no means accurate because they are measured from the outside of the cup. But with properly configured limits you’ll be able to specify useful temperature zones like cold-warm-hot. Also, when the cup is cold, the setup doubles as a room thermometer.
