Moisture Monitor for Plants

Over-watering and under-watering both are harmful for plants. Roots need air as well as water. If the soil is constantly saturated, air cannot reach the roots and they suffocate. Also, excess water weakens the plant and makes it susceptible to various diseases, particularly fungal attacks. Under-watering, on the other hand, is equally harmful. Plants not receiving enough water droop from the top down and leaf edges turn brown.

Moisture monitor provides a solution to the above problem by monitoring the moisture level of the soil and producing an audio-visual alert when the moisture goes below a preset level, indicating that the plant needs to be watered.

Circuit and working

The core of the circuit is inexpensive and built around popular 14-stage ripple-carry binary counter CD4060  and a few commonly available components. Not all the outputs of the binary counter are available externally. The frequency at pin 7  of IC1 is actually divided by 24=16 compared to initial astable frequency. Similarly, Q4 will have half the frequency of Q3. Components R3, R4 and C2 set the clock oscillator frequency to control the flash rate of LED1 and the beeping rate of PZ1. Pulses are enabled when reset pin 12 is low and disabled, or inhibited, when reset pin is high.

Tthe circuit is simple and straightforward. The base of transistor T1 is connected to a gimmick potential divider comprising sensitivity control preset VR1, fixed resistor R1 and the moisture sensor probe. In standby state  IC1 is disabled because its reset pin 12 is directly tied to +9 V through resistor R2. However, when the soil is dry, transistor T1 is forward biased by VR1 and R1. This enables IC1 to oscillate. As a result, LED1 starts blinking and piezo-buzzer PZ1 sounds to indicate that the plant needs water.

PCB and component layout

The whole circuit in a suitable crystalline tube or box. The moisture sensor probe can be constructed using two small metal rods mounted vertically with a small gap about 10 mm in between them. These two metal rods must be supported by a small insulated board. You can place one flora caretaker in each plant pot for constant monitoring of soil moisture.