I’m slowly going crazy. I’m having a problem where my excel formulas are telling me the analog val (aval) is much higher than what is the output on the Spark core.

You can scroll out the graph with your mouse and move it around by clicking on it. Centre it so you can see the whole thing. The graph enables you to set a fixed resistor and choose the thermistor type. I have the ET-732 piece of crap. According to the maths on the graph, and my maths in my excel (https://drive.google.com/open?id=0B3NyXvs_xmuIa1ZleHhtOUNMaUE&authuser=0), 66Fahrenheit (roughly 19C room temp) should present to the controller as an analogue value of ~3957. That’s nicely within the upper bound of 4095, so the 45k resistor seems to be a good choice.

The trouble is, I’m not seeing anything close to an analog value of 3900 odd, its mostly sitting around the 3100 analog range. Either the coefficients are well out (I took them from Heatermeter and tried numerous versions) or the analog value is for some reason not what it should be.

My circuit is currently simple, a voltage divider resistor (tried 1k, 10k, 20k, 45k, 68k) and a 0.1cu ceramic cap. Using a spark core, ET-732 temperature probe, breadboard. Power via USB or 5v wall wart has been tried.

Suggestions on formula, circuit etc are most welcome