Flower pot water shortage alarm circuit

Whether the flowers in the pots need watering or not is sometimes unreliable just by observing whether the soil on the surface is moist. To this end, a potted flower water shortage indicator is made
. When there is a lack of water in the pot, the indicator emits a flash signal to remind people to water the flowers.
    The circuit of the potted flower water shortage indicator is as shown in the figure. The circuit is mainly composed of field effect transistor VT1, transistor VT2 and a 555
time base circuit.
    When there is a lack of water in the soil, the resistivity of the soil increases greatly. At this time, the resistance between the M and N points is very large, and the N channel The gate of junction field effect transistor
VT1 is close to the negative supply voltage, so VT1 is turned off. At this time, the base of transistor VT2 obtains bias current through resistors Rz and R3, and
VT2 is turned on. The potential of the VT2 emitter rises , causing the 555 time base circuit to work.
    Since the time base circuit is connected into an ultra-low frequency multivibrator, its oscillation frequency is about 1Hz. When the basic circuit is working, the light-emitting diode will
flash red light with the frequency of the low-frequency oscillation signal, reminding people that it is time to water the potted flowers.
    When the pot soil is not short of water, the resistivity of the soil is very small. It is equivalent to a small resistance between M and N, so the gate of VT1 is almost connected to
"ground", the gate voltage is close to ov, and the drain and source are connected. When VT1 is turned on, its drain potential drops, causing VT2 to cut off, and its emitter potential
also drops to the "ground" potential . As a result, the time base circuit stops working, and the light-emitting diode LED no longer emits light.
, when VT1 conducts wine, VT2 cuts off, and the time base circuit does not work, the power consumption of the entire circuit is very small, about ImA. Therefore, if the power supply is powered by AA
batteries, it can be used for a long time. ,
    when using, use two stripped wires as two electrodes , insert them into the soil of the flower pot, and the two electrodes should be a few centimeters apart
. If the circuit does not need to work at ordinary times, just connect a small switch in series to the positive power supply circuit. The consumption is very small, and
the battery can be replaced for a long time.
    The rated current of VTJ in the circuit is 0.5N 5mA, and the pinch-off voltage is about 4V. Use 3DJ6E, 3DJ6F or 3DJ6G. When VT2 uses 3pG6,
the base circuit can be NE555.