The base setup for this system is located in a room with approximate dimensions of 9.29 square metre. The room is non-air conditioned and does not receive any direct sunlight. The proposed setup aims to evaluate the feasibility of utilising an electrode-based E201 BNC pH measurement sensor for assessing the pH of the water before and after the addition of liquid nutrients.
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Fig. 1 illustrates the authors’ prototype showcasing various aspects of the setup and its installation. Monitoring the pH value is crucial for maintaining optimal conditions for plant growth. The ESP32 is employed in deep sleep mode, and with the assistance of a touch sensor, the pH of the hydroponic solution can be measured with a simple touch. This touch sensor acts as an interrupt, triggering an external input for the ESP32, thereby awakening it from deep sleep mode. Fig. 2 provides a block diagram representation of the entire setup.
pH reflects the hydrogen potential in a solution, providing a numerical value that determines its acidity or alkalinity. The pH scale ranges from 0 to 14. A pH value below 7 indicates acidity, while a value above 7 indicates alkalinity. pH serves as a vital chemical indicator for hydroponic setups, reflecting changes in water due to the addition, absorption, and balance of liquid fertilisers. Common indicators such as phenolphthalein, methyl red, and bromothymol blue are utilised to indicate pH ranges of approximately 8 to 10, 4.5 to 6, and 6 to 7.5, respectively.
Phenolphthalein transitions from colourless to pink, while methyl red transitions from red to yellow. This term, widely used in chemistry, biology, and agronomy, translates the concentration values of hydrogen ions, typically ranging between about 1 and 10–14 gram-equivalents per litre, into a scale from 0 to 14.
The pH of a solution can be calculated by taking the negative logarithm of the hydronium ion concentration, expressed as pH= -log[H3O+]. At 25°C, a solution with pH<7 is acidic, pH>7 is basic, and pH=7 is neutral.
There are two methods for measuring pH: colorimetric methods utilising indicator solutions or papers, and more accurate electrochemical methods using electrodes and a millivoltmeter (pH meter). We are employing the latter method with the aid of a microcontroller circuit for enhanced accuracy in readings.
Plants have varying pH requirements; however, a pH range of 5.5 to 6.5 is generally considered optimal for hydroponic gardening. Most plants thrive in slightly acidic conditions. The commonly used chemicals to adjust pH are phosphoric acid (to lower pH) and potassium hydroxide (to raise pH).
While both chemicals are relatively safe, they can cause burns and should never come in contact with the eyes.
Specific nutrients necessitate certain pH levels for optimal plant uptake. Incorrect pH levels can lead to deficiencies in certain nutrients or toxicity. For instance, when the pH level drops below 5.0, plants may develop magnesium and calcium deficiencies, or copper and iron toxicity. Fig. 3 illustrates a typical pH scale and its correlation to everyday objects in our lives.
ESP32 power modes
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