So using the comparator I got the circuit to work. It works fine with the 3.3v off the arduino. However, I used a potentiometer as the comparative voltage to the tmp36. I'd like to change that so that it is a fixed voltage. Unfortunately, I have hit somewhat of another conceptual road block.
According to my understanding I have the following options for doing a fixed voltage. (In the cheap and small range)
Option 1: I could use two resistors to create a current divider. This would achieve the objectives of being cheap and small.
Problem: I plan to hook the circuit up to a battery. So, according to my understanding, as the voltage drops in the battery over time the amps out of the current divider is going to drop as well. As such, this doesn't really provide a fixed voltage over time.
Option 2: I could use a zener diode.
Problem: According to my understanding this would have the same issues as a current divider as voltage changes on the battery.
Option 3: I could use a voltage regulator
Problem: Perhaps this is the best option but I have some concerns regarding it. First, the little research I've done implies that a voltage regulator requires at least 2 volts above the required fixed voltage. So if I was looking for a fixed voltage of something like 0.85 v then i would have to have a battery that does 3 v or more. Which is fine. But I got so excited over the fact that I was using so little voltage that I decided to play a little game to see how little voltage I could use to make the circuit work. It would be a shame if the only reason that I was using 3V was because I had to use the voltage regulator which would output 1V and then I would have to reduce that down just a little bit more.
Another issue is that the voltage regulator can give off a lot of heat which has me concerned that it might affect the TMP36 sensor. This issue probably isn't that big of an issue. It just crossed my mind.
So... guru's what other options might I have missed that could give me a fixed voltage. Or did I make a mistake in my understanding from above?