Hotel key-card power switch teardown

This is the switch on the wall of hotels that only turns the power on to things like lighting and air conditioning while a guest is in the room. I was expecting this to actually sense an active card, but it's simpler than that, which also allows it to operate with a plain key identification card.

For some inexplicable reason I said LM324 (quad op amp) instead of LM358 (dual op amp) which I was thinking of. All the more impressive because I hardly ever use LM324s.

The modular approach to this design makes me wonder if there are other units that use the same power and relay base, but a different daughter board to implement other functions.

Although the instructions show the bezel and module as separate items, and mentions clipping the module into the frame, you can also just slide the front white plastic card holder up to remove it.

They win mega points for the main power PCB for robustness, electrical separation, and the decent relay. One slight twist could have been to shuffle the PCB and sandwich the thermal fuse between the relay's contact side and the MOV to add an extra layer of protection against burning contacts. The thermal fuse on the MOV transient suppressor is excellent. They tend to have an end of life failure mode of heating up, and a lot of products use them without allowing for that.
It would have been good to swap the positions of the power supply zener and decoupling capacitor to space the warm zener away from the electrolytic capacitor.

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