Make my Arduino emulate temperature sensor


I have an oil boiler with a defect temperature sensor. The sensor is just a piece of bend wire, and it is now in 2 pieces. The sensor is probably custom made and the manufacturer does not exist any more. I guess the electrical resistance in the wire changes with temperature.

My question is if it is possible to replace the damaged sensor with a digital variable resistor controlled by my Arduino. Then I can use a K type or J type thermocouple, which I have, to read the temperature in the boiler and send this signal to the Arduino. Then the Arduino can "translate" this signal and control the digital resistor connected to the electrical circuit in the boiler.

I guess I need an IC for the K type Thermocouple and a digital variable resistor replacing the damaged sensor. Do I need any more parts? Any thoughts on how or if this will work? I have an Arduino Duemilanove, if it matters.

take insulation of both wires for 1 cm. twist them together, give it a bang with a hamer problem fixed.


The wire sensing temperature is only about 5 cm long, and is now in two parts. There were 2 wires with insulation soldered to the two ends of the sensing wire. Since the sensing wire now is damaged and will be shorter than originally if I connect it again the temperature reading will be wrong.

Hi jan,

Did you get any further with your k type thermocouple project, I'm trying to find info on the same subject.



Get hold of some thermistors, which are resistors the resistance of which varies with temperature. With some, resistance goes down as temperature increases, with others, the opposite. Then build a voltage divider out of a fixed resistor on your circuit board (not in the environment to be measured), and the thermistor, and use the ADC capability of the Arduino to measure the voltage, at the centerpoint of the voltage divider, from which you use Ohm’s law to determine the resistance of the thermistor.

Thermistor data sheets usually supply the data needed to convert the thermistor’s calculated resistance to a temperature. I’ve played a number of “fancy” temperature sensors (LM35, DHT 11), but thermistors generally are the most durable and reliable for your type of application.

Hope this helps.

John Doner