One of the original applications I had in mind for MRBus was monitoring a compost pile I build each spring using manure from our horses. In early summer, pumpkins are transplanted into the pile and do remarkably well. In fact, I discovered this by accident one year – some pumpkins one fall were added to a pile of manure and allowed to compost. The following summer, volunteer pumpkins grew and were some of the largest and healthiest looking I had ever been able to grow here in Colorado!
Single-point calibration of the RTS node is easy to perform. One method is presented here using the water ice-point and works with both waterproof and non-waterproof temperature sensors. The RTS firmware provides both offset and gain calibration coefficients. For most purposes, a single point offset calibration is probably sufficient. To accurately perform both gain and offset calibration requires more sophisticated VBE equipment and is beyond the scope of this investigation.
Simple P-N junctions, as found in bipolar transistors, exhibit a very useful property that can be used to measure absolute temperature. When biased at two different currents, the difference in voltage across the P-N junction is linearly related to absolute temperature, with little dependence on semiconductor process variations.