Hello, I have an application that reads some analog sensors (LDRs) in a fairly harsh environment. I would like to write a function that periodically polls the readings and detects fault conditions. A short to ground is easy to detect, and a short to positive will shut down the board, but the most common fault is a broken wire, and since the pin is now floating around 500, which is also a valid reading if it were working properly, I cannot figure how to differentiate a fault. I tried 10K pull-downs, which distorted the readings too much. (Unsurprisingly).
Will 1M pulldowns work, perhaps? What are your thoughts? What about the internal pull-ups? My feeling was that 30 -50K may also be too strong, but I suppose it would be easier to try....
Also, a related question. When I was perusing some data sheets, I saw that all of the arduinos analog pins share one ADC unit and it's capacitor. I also saw that a call to analogRead takes about 200 microseconds. Is that enough time for the capacitor to drain between subsequent analogReads? Or should there be a delay between readings? My feeling is that an extra delay is not needed, and there certainly doesn't seem to be much mention of it, but I'm just curios. (I'm not sufficiently math-savvy to calculate the relevant values from the datasheet.)