relay logic

I've never heard of that being a problem. None of the books I have on telephone exchanges (which used thousands of relays) mention it. Countact bounce shouldn't be a problem either (well, maybe if you're interconnecting very different relays, trying to control a high-speed reed relay from a much slower type thing...). The response time of the driven relay won't be fast enough to respond to contact bounce. Be warned if you look at some of the telephone exchange circuits that they used (at least in the UK) some odd relays. Not only make-before-break changeover contacts, but also slow-energise and slow-releasy relays (copper 'slugs' in the coil was one way to get this IIRC). You may have problems finding that. Incidentally, I made a relay flup-flop without realising it a few months back. I had a pair of contactors (high-power relays, basically) that were mechnaically interlocked so they couldn't both close together and electrically interlocked so that the 2 coils couldn't be energised at the same time. The latter was done by feeding each coil through a normally-closed contact on the other contactor. Anyway, if I turned on the supply to one contactor (let's call it 'A'), it pulled in. Turning on the supply to the other one ('B') did nothing (since the current path to B's coil was broken by the NC contact on A). But now if I turned off A's coild supply, A dropped out and B pulled in. I could then turn on the supply to A again and nothing happened until I momentarily opened the supply to B. Of course this is exactly what was supposed to happen and I fairly quickly relaised it was logically equivalent to a pair of cross-coupled NOR gates -- the classic Eccles-Jordan circuit. -tony