4.1.8. Step-Down Voltage Regulator

The smart drip irrigation system is powered using a 12 V DC adapter. We used a step-down voltage regulator to supply the ESP32 with the 5 V needed for operation.

#### *4.2. Drip Irrigation Setup*

#### 4.2.1. Acrylic Container

To make our irrigation system somewhat portable, we made an acrylic container. We first cut out the base and walls of the container from an 18 mm thick acrylic sheet using a computerized numerical control (CNC) machine and then glued them together and applied silicone, as shown in Figure 9a. Once the glue and silicone were dry, we added some screws to the container for strength and drilled drainage holes in the base of the acrylic container to allow for percolation, as shown in Figure 9b. The diameter of the holes ranged from 10 to 12 mm.

(**a**)

(**b**)

**Figure 9.** Preparing the acrylic container. (**a**) Curing the super glue and silicone. (**b**) Drainage holes drilled in the base of the container.

#### 4.2.2. Soil

After preparing the container, we poured in one and three-fourths of a 50 L bag of all-purpose potting soil [34], as shown in Figure 10. This translates to 6.280 inches of soil, which is sufficient for growing green onions as they require 6–8 inches of soil [35]. The soil is a mixture of organic compost and moisture-retaining coir residues that prolong hydration and reduce drought stress, making the soil quite useful for the subtropical desert climate of Qatar. The elemental analysis of the soil is shown in Table 1.

**Table 1.** Test results of the elemental analysis of the soil [34].


#### **Table 1.** *Cont.*


**Figure 10.** Adding soil to the container.
