Comparing two thermistor inputs

I need to compare temperatures of two thermistors. When that delta reaches 1 degree, I need a DC control signal output.

How can I do that?

Can you read the temperature of one thermistor? Once you can do that, you can read the temperature of a 2nd one, and C++ is really good at math! :D

So, it's a simple matter of subtracting the two readings and checking to see if the absolute value of the difference is less than or equal to one.

I need a DC control signal output.

Is 5V OK? The Arduino's digital outputs are ~5V when high and ~0V when low.

FYI - In most applications, it's easier to use an LM34 (Fahrenheit) or LM35 (Centigrade) than to use a thermistor. These devices put-out a voltage that's linearly proportional to temperature. They are also fairly accurate "out of the box" so in many applications no calibration is necessary. You probably will have to calibrate your thermistors.

A thermocouple is inherently super-accurate, but it requires a thermal reference (such as an ice water bath) or a simulated reference and it requires amplification which can be a source of noise and drift, so it's not an easy thing to use.

P.S. If this is for some kind of control system, you probably also need to know which temperature is higher when they are not within one degree.