te:
s, D, Tr, Q, BR etc
t ones in my truck alternator. The bridge I just notate as D. It's drawn on the schematic as a diode bridge, so why add a special ref des especially a two letter one? I don't think I've ever used a two letter ref des.
s (much as D is adequate for diode bridges) and J is the typical designator for connectors. Why buck convention?
Ok, to each his own.
I don't recall ever seeing CN on a schematic. I have seen J and P used for jack and plug, but as others have indicated, the terms jack and plug are n ot so clear with some connector types. In many cases I've seen J used on a ll connectors, so I now just use J.
I also don't recall ever seeing IC used for devices.
One place where I have seen variations is both X and Y used for crystals. I can't recall any other variations in the standard designators, but there may have been some. As others have mentioned, it is not uncommon for board s to be crowded so that two letter ref des would need space that might not be available. I know the stuff I design is often *very* crowded. In one c ase I had to put the ref des over top of vias and had to deal with the PWB fabricators wanting to clip excessively around them. We discussed the conc erns and I got them to only clip close to the hole and not around the entir e pad making the ref des legible again.
Rick C.