Soil moisture sensor was intended to be used (by me) to check if the plant needs water, however, this is not a good approach. Different plants have different needs and the soil moist sensor cannot yield consistent results.
For instance, we water the plant and the soil dries out after one or two days. Now, the soil moist sensor will pick up this detail and tells the MCU to water the plant. BUT, if the plant only needs water once a week, this approach isn't appropriate since it will water the plant more than once a week.
Solution
We will use soil moist sensor to determine if the watering is sufficient and the MCU can turn off its water pump. Specifically, we put the sensor at near bottom. This way, we know if water has penetrated all the way down to the bottom, then we turn off the pump, instead of enabling the pump for a specific amount of seconds.
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Solution