My first computer was a Heathkit H89 that my dad assembled about 1980. It had a keyboard microcontroller (I don't remember, maybe an 8048), but it also had hardware debounce: the keyswitches snapped together a solid copper electrode, on one side, and four copper "fingers" on the other. The idea (as he explained to me) was that the fingers would bounce out-of-sync with one another (although they looked pretty identical, maybe there was a subtle difference I couldn't see) and there wouldn't be any time when all four of them were out of contact at once.