K2 closing the power switch, and then press the button switch K1, then Crystal diode V1, V2, and the relay sucks and shuts. The power charge the capacitor c. After first K1 because c has been charged, it will by r and V1V2 discharge, so as to sustain the turn-on transistor, relay sucks and shuts. After a period of discharge, c bipolar voltage drops to a certain value, not enough to sustain the turn-on transistor, relay release. Disconnected from the K1 relay release time interval called the delay time. It depends on the size of r and c. C-100 micro law, adjust the adjustable resistor r will get 10 seconds to 90 seconds of delay time. If c is 1000 micro-method, then the delay time of 5 minutes or more.