555 flowerpot deaquation alarm circuit

Published:2011/6/7 2:00:00 Author:TaoXi | Keyword: 555, flowerpot, deaquation, alarm | From:SeekIC

As the figure 15-5 shows, the low-frequency multivibrator is composed of the 555, the oscillation frequency f=1.44/(R5+2R6)C. When the pot does not dry, the resistivity of the soil is small, the voltage between the VT1's G pole and the circuit's ground voltage is nearly 0V, VT1 conducts, VT2 cuts off, so the voltage of the VT2's emitter is 0V. At this time the 555 is in the non-trigger state, pin-3 has the low electrical level. When the soil is dry, the resistance between A and B increases, the electric potential of the VT1's G pole is nearly the negative pressure, VT1 cuts off, VT2 conducts, VT2's emitter potential increases. According to the features of the 555 time-based circuit, when the electric potential of pin-4 is higher than 0.4V, the 555 might be in the oscillation condition, the output port pin-3 has the high electrical level, and the LED's frequency is 1Hz.



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