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As shown in this circuit for the pot dry . The circuit consists of two humidity probe A, B, multi- harmonic oscillator, light-emitting diode LED and other components. One oscillator from the 555 and R5, R6, C , etc. , whose oscillation frequency is f = 1.44 / (R5 2R6) C, shows the corresponding parameter of about 1Hz. When the pot is not water shortage , A, B resistance among smaller , BG1 gate G to the circuit to the voltage close to 0V, so that N -channel JFET conduction BG1 , BG2 corresponding cut-off , the radio Great potential of 0V, 555 feet is low because of and in non- trigger state , pin output low .
When the pot water shortage , A, B between the resistance increases , BG1 gate G potential due to negative pressure which is close to closing , BG2 conduction , the emitter potential of the corresponding increase in BG2 . When the potential to rise to 555 pin potential is high (0.4V) , the oscillator start-up , the output from the oscillation signal foot drive LED flashing 1Hz LED issued to inform the watering . If received within 3 feet for a small speaker , while R5, R6 or C decreases, so that the oscillator frequency f for child hearing, the role also serve as a reminder .