1. The problem statement, all variables and given/known data I think I know how to do this but wanted to make sure before I actually make the circuit. Here's a general diagram: [PLAIN]http://forum.allaboutcircuits.com/image_cache/httphome.cogeco.ca~rpaisley4ComparatorWindow.GIF [Broken] So as you can see I'm trying to make a window detector circuit that makes an LED turn on if the voltage is below or above a certain threshold. In this case, I want the LED to turn on above 2V or below 1V. 2. Relevant equations I think I know how to devise the relevant equations: VREF1 = R3 / (R1 + R2 + R3) * V+ VREF2 = (R2 + R3) / (R1 + R2 + R3) * V+ 3. The attempt at a solution I'm just unclear on what to make R values. It seems that R2 always comes out as 1/2, which makes sense mathematically (if you set VREF1 = 2, VREF2 = 1) but makes no sense to me in the real world. I've always used resistors with usually at least 100 Ohm values. But maybe I'm wrong. Help?