Posted on Aug 28, 2017 10850
When the water level decreases so as to dry the portion between electrode, earth and electrode connected to the N10 input, the input of N10 through R10 will become HIGH. So the output of N10 will become LOW. The LED D11 stops being switched off and extinguished. D1 - D9 remain unaffected, ie off. But the D10 lights up. Because its descent is LOW by the output of N10 and the rise of HGH through R23 and the output of N9. From now on, the operation is simple.
Whenever the water level drops below a graduation (ie contact) of the device, the corresponding LED diode turns on. Thus, water in the soil is easily detected. If the drought in the land on which the pointer is pulled is increased so that it stops and the last road (towards the N1), the last LED of the series (D1) will turn on and then the diode system D13 to D16 will activate the unstable multiplier Formed by N11 and N12. The LED D12 will now start flashing, indicating the immediate need for watering. Since D16 is connected to the N10 output, D12 will continue to blink until the water level rises to the N10-corresponding field.
Unfortunately, there is no ready PCB image but it is not difficult, so most could design a proper printed circuit on their own. Of course, the correct length of the moisture detection section and the distance between successive sections will depend on the size and shape of your pot.