19-10-2017, 11:52 AM
Rain alarm
Working: Water is a conductor of electricity. When the water is in contact with the probe, then there is a current flow towards the base of the NPN transistor (BC548), which leads. With the conduction of the NPN transistor, the electron reaches Q2, which is a PNP transistor. The PNP transistor (BC558) also conducts and the current flows through the speaker. In a loudspeaker there is an inductive coil that causes movement in one direction and then produces induced current, which is in the opposite direction to the current flow, this induced current in pulse form, flows through a capacitor, resistance and causes the first transistor BC548 off for an inter-well and after-that is relaxed to the previous state. This process is repeated over and over again until the probe is in contact with the water and an oscillation in the circuit is created. The speaker diaphragm vibrates and gives a tone. The frequency of the circuit depends on the value of the impedance of the coil, the capacitor and the resistance value.
![[Image: rain_alarm.gif?189db0]](http://circuiteasy.com/circuit_diagram/rain_alarm.gif?189db0)
