- 50 switches
- Debounce both contact closure and release
- Single interrupt for all events
- Process the key press events


Stated simply that is quite a bit of workload on the processor, assuming you get it going.

And as Erik pointed out every switch has a minimum current rating for reliable switching. Our member Kai Klaas has posted a good article on this - maybe you will find in threads discussing "debouncing". Suggest read that first.

Also why are you handling all switches at one go ? After all the house and its rooms will be spread over an area and it would be easier to control them in "blocks" of say 10 switches or less. You can have a master MCU and many such sub-MCUs. The sub-MCUs are responsible for the local blocks and the overall status is controlled by the master - maybe you can use an RS485 for this comm. And possibly cut down on the "noodles" of wires all over the house...

Also it will ensure that in case of a fault in one block, the others are still kicking OK. You would not like the light in the toilet go off when someone in the bedroom switched off his light ? Or vice versa ;-)

Raghu