[General] Epoxy Air Temperature Sensor interfacing with microcontroller

[Ow@i$]

Hello,
I have a temperature monitor circuit that I want to reverse (code)
it uses Atmega64 and this sensor.

The circuit is attached, by changing the temperature manually I have noted down corresponding voltage at ADC, what I need is a GENERIC FORMULA based on the readings, is this something you guys can help?
(I couldn't find datasheet of the sensor that can help in someway)

Regards
Owais

 

[pic.programmer]

What is the maximum temperature the sensor can measure. The page mentiones that it is a NTC type thermistor. Are the output of the sensor linear ?

 

[Ow@i$]

The sensor page mentions that it can measure max of 105-deg-celsius,
I have recorded the voltage values at ADC pin it is linear w.r.t temperature i.e voltage increasing when temp decreasing.

some values that I measured
-40degree---- 4.86V (ADC pin)
-39degree---- 4.84V
-38degree---- 4.82V
.............................
16degree------3V
34degree------2V
.............................
99.5degree------ 0.31V

 

[Easyrider83]

Linear Fit: y=a+bx
Coefficient Data:
a = 1.03051064681E+002
b = -2.95414214869E+001

Real Temp = a + b * ADC_Value

 

[Ow@i$]

How so?
where do you get a & b?

 

[Easyrider83]

Try to use 'curve expert'
Very simple tool.
Better use 'code to temperature' conversion. Not 'voltage to temperature' because anyway you will have to transform code to voltage first.

 

[Ow@i$]

@Easyrider83

Well thanks there mate, I plugged in the data and went for a 3rd degree non-linear equation to get all values covered, result was good! curve expert is a handy tool indeed!

 

[Easyrider83]

I think for you purpose linear dependace will be enough. 3rd degree equation require a lot of calculations with floating point. For 8-bit mcu it can take something about few ms and a lot of RAM.

 

[Ow@i$]

well the linear equation was giving a error of about ~5 degree in temperature (for some values), I didn't went for the 4th order because of the mcu limitations, 3rd was a tradeoff!
It is working fine for now but if it didn't I will move to the second order. Thanks