Hey fellows, couple of questions. I have a led on my Fridge that lights up every six months telling me its time to change the water filter. I'm assuming its using a 555 chip or some timing circuit to turn this light on every six months. To turn this led off, you have to press a reset button. I actually change the filter every two years or when I noticed the water flow start slowing down. My Cuisinart coffee maker has a red light light come on when the maker supposedly needs cleaned. I havn't noticed any set time when this coffee maker decides that it needs cleaned. Here is my question. After I go through the cleaning routine with the white vinegar, the red light goes off by its self. I didn't unplug it or reset anything. this is a $50 coffee maker. How did it know if I actually cleaned it or not? What kind of sensor could determine this? Thanks!