add temperature compensation to ec sensor firmware

[gordonbrander]

the ec sensor assume the water to always be 25 deg C, this is not a fair assumption

however, the sensor temperature compensation can be set. so if we subscribe the sensor to the water temp topic our readings should be accurate.

background on the problem: when trying to study how to close the ph / ec loops, i filled the basin with cold water, over the course of the experiment it had a significant effect on the ec: @10.25C EC=0.31ms/cm @11.94C EC=3.28ms/cm For context, the operating range of the nutrient solution recommends using a range between 1.2 and 2.4 ms/cm

to qualify, these sensors are supposed to come factory calibrated so i did not verify calibration. can do that one calib solns come int

also, over the course of this i was actually running a ph dosing experiment so this was not an isolated experiment

regardless i still think we should use the temperature compensation feature supplied by atlas's circuit since we have the water temperature

(Exported from Trello https://trello.com/c/Vn63RxAh/887-add-temperature-compensation-to-ec-sensor-firmware)

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On 2017-03-30T20:39:11.994Z, @gordonbrander wrote:

Related to another EC sensor issue. We should be able to use EC for proxy to Ph, but dosing nutrients constantly increases EC.