I actually just wanted to know in theory if a comparator would do what I described. I understand a comparator "compares" two dis similiar inputs, lets say: Input A is: 12V and Input B is: 6V and both inputs are available there is: 0V output, until a loss of one of the inputs the larger will become the output. Example A=12V B=6V , a loss of input "B" will create a high (positive) output of: 12V (1+1=0) (1+0=1) I am actually just beginning to work with that type of integrated circuit incorporating it with the ones I have learned (Im a hobbiest only electrician by trade) I know the 555's and 4017 counters, I try to know everything about them before I use them and I picked one up from RS and just did a quick read on them. From what I read you give the chip 2 different inputs and the loss of one input causes an output so I guess thats a OR logic? In one state its an AND in the other state its an OR or maybe Im getting it wrong maybe they would be NOR and NAND ????? Thanks in advance, Jim