loose-electron wrote on Aug 3rd, 2008, 3:43pm:A suggestion on using fuses, DONT let it define a logic state directly. Take the voltage created (with or without blown fuse) and feed that into a comparator to generate a logic state.
The reason for this is that a blown fuse can have a lot of resistance variation from fuse to fuse, or the residue from blowing the fuse can shift and change the state of the "open connection" --- That open connection may actually be 80K (or similar) of resistance.
Using the comparator allows you to define a circuit that can tolerate a lot of variation in the blown fuse and still work properly.
An excellent point from Jerry.
Actually, poly fuses or other fuses are usually built into a module containing comparators and all necessary support blocks for this very purpose. Otherwise, one would have very unreliable operation, particularly over time.
So be careful not to build your own versions, unless you plan to build several of them and characterize them in detail first before you use them in your real system.
Vivek