Set range for analog value with AdcParam

[robin13]

I am using an analogue capacitive soil moisture sensor which outputs a voltage. Reading using the Analog input on A0 I get a value between 720 (dry) and 200 (wet). That's small subsection of the entire range 0 -> 1023, but also it is very difficult for me to represent in my head (or in a graph) how "wet" the soil is when I e.g. get the value 250 (quite wet). What I would like is to be able to output the equivalent 0->100 reading. I imagine this being configured with AdcParam something like:

AdcParam 4 200 720 100 0

Where 4 = Remap analogue values. <param1> = lower limit <param2> = upper limit <param3> = value for lower limit <param4> = value for upper limit

In the example I have deliberately set the value for upper limit to a number lower than the value for upper limit because in my example I want 0 to be "dry" and 100 to be "wet", so while <param1> should always be less than <param2>, <param3> and <param4> should just be a range where it is not important which is greater. So going back to the example above, the value 250 would be:

int( ( ( (<param2> - <analogue-value>) / ( <param2> - <param1> ) ) * ( <param3> - <param4> ) ) + <param4> )
or
int( ( ( 720 − 250 ) ÷ ( 720 − 200 ) ) × (  100 − 0 ) ) + 0
= 90

So the result 90 (of 100) is much more meaningful than 250 as a measure of "wetness".

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