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### Topic: Oven Temperature Sensor (Read 2856 times)previous topic - next topic

#### MikeCole

##### Apr 30, 2014, 03:38 am
Hi everyone,

I'm looking into interfacing an existing oven temperature sensor to an Arduino.

The oven sensor is a resistance based sensor varying resistance between 1143 ohms @ 100 F to 1949 ohms @ 500 F.

Someone suggested hooking it up like a photocell with an analog pin but I am concerned that I would not get the full range of detail as the photocell goes into the K ohms range and the oven sensor does not.  I'd like to be able to adjust it and then perhaps build in a table or formula to get a flat response.

Does anyone have any idea for the best way to do this?  Constant current source, perhaps?  I'm new to all of this.

Thanks
- Mike

#### robtillaart

#1
##### Apr 30, 2014, 12:19 pm
make a voltage divider
5V -----[2K2] -----A-----[temp sensor] ---- GND.

The A is connected to the Arduino analog port
The voltage at A will be between
1143/(2200+1143) * 5 Volt  =~ 1.7V
1949/(2200+1949) * 5 Volt =~ 2.34V

If you use an external reference of 2.5V for the ADC giving these readings
1.7V  ==> ~695
2.34V ==> ~957
// these numbers should be callibrated manually as the 2K2 resistor has some tolerances.

Then you can do

int temp = map(analogRead(A0), 695, 957, 100, 500);  // linear interpolation

get the idea?

(the assumption is that the temp is linear with resistance)
// above might contain some math error
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

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