It often happens when someone from the household forgets to turn the lights off in the toilet — he may be there without the use of a lot of hours. A simple automatic device which, when necessary, turns on the light in the bathroom, and when not — turn off. The electrical circuit of such device is presented in figure 1. It contains: a low-power transformer T1, rectifier VD1 — VD4, filter capacitor C1, two limit switches SB1 and SB2 relay K1. How the device works and how it performs its functions?
When the door is closed, the limit switch SB2 is open, as the relay K1, the light in this position on the toilet does not burn.
Open the door — limit switch SB2 closes the relay K1 and the lamp illuminates.
She came into the bathroom, closing the door on the latch. This closes the second limit switch SB1, is triggered and remains closed the relay; the light will continue to burn until the limit switch is not open.