Automatic Room KeyCard Power Switch

Hotel rooms are often furnished with an interior key-holder near the main door which enables the ac power supply to everything in the room only when the key/keycard is hanged/inserted. The circuit given here to flip electric lights (and other appliances) is along the same lines, but the solution is amazingly simple and inexpensive!
A bump switch (S1) is attached to the circuit, and its long lever arm is extended to the outside such that when the key card is hanged on it the bump switch is closed. Now, the electromagnetic relay (RL1) will pull in and complete the circuit for all the ac-powered appliances in the room. As soon as the card is removed,the bump switch will open, and this in turn releases the relay contacts. Various connected appliances will automatically (and inevitably) be switched off after a short delay when the room key is picked up from the key-hanger.
Schematic of the KeyCard Power Switch Circuit

The circuit described here does not require an AC power transformer. Instead, the voltage is reduced by series capacitor (C1) connected directly to the mains voltage via an inrush current limiting resistor (R1). The AC230V voltage is rectified,and limited by the peculiar diode bridge configuration (D2-D3 + ZD1-ZD2) and the resulting steady dc voltage of 12 volt is smoothed by the electrolytic capacitor (C2). The “always-illumed” visual indicator (LED1) works as the key-holder location finder. Finally, toggle switch (S2) can be used to bypass the automatic switching function, in case of an emergency.

The entire circuit should be fitted in an insulated enclosure, since it is connected directly to the ac powerlines. Note that the coil of relay RL1 must be have a low operating current (no more than a few dozen milliamperes). The author used a type HRSS 4H-S-12V DC (from 3NIX) in the prototype. The 3NIX sugar cube relay draws near 26mA at 12V DC.
At first glance, many readers (and evaluators) might think this circuit is superfluous because only one heavy-duty bump switch can play the game well. Yes, but it is highly-flexible and leaves enough room for expansion. An interested hobbyist can make numerous modifications like key-card based activation, remote switching control, etc (ofcouse using galvanic-isolators) without too much difficulty. I will keep those as surprises for future designs!