arduino yogurt maker


Posted on Feb 6, 2014

The crock pot is attached to a relay that can switch it on or off. The relay is toggled by a microcontroller based on readings from a temperature sensor ( thermistor ) placed inside the crock pot. Heat the milk to 185 °F (85 °C). This kills off microbes to make way for our yogurt cultures, and denatures enzymes in the milk that may interfere with


arduino yogurt maker
Click here to download the full size of the above Circuit.

yogurt culture growth. Doing things the old-fashioned way, I`d be using a stovetop and candy thermometer for steps 2 and 3, then a warm oven or a radiator for step 4. That takes a lot of attention, and uses more containers than I care to wash later. Many commercially-sold yogurt makers still require you to perform step 2 yourself. With the Arduino setup, I use a few canning jars in a water bath inside the crock pot to ensure even heating. I submerge the temperature sensor in the water. A voltage divider circuit is used to indirectly measure the resistance of the thermistor. In the code, I make use of the Steinhart-Hart Thermistor Equation to translate the thermistor`s resistance into temperature. This gives a pretty good idea of the temperature inside the crock pot. In addition to the thermistor`s resistance at a given time, the Steinhart-Hart equation needs to be fed three coefficients which can be calculated from information on the manufacturer`s data sheet based on predetermined resistances at different temperatures. Since we`ll be measuring a range between 100 °F (38 °C) and 185 °F (85 °C), I used resistance values measured at 86 °F (30 °C), 140 °F (60 °C) and 194 °F (90 °C) to calculate my coefficients. Here`s a simple calculator to calculate your coefficients from a given temp/resistance range, and here`s a more in-depth explanation of the math involved. Since the temperature readings will be taken in the water bath,...




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