Hydroponics is a newly emerging agricultural technology that enables us to grow plants without the use of soil. When soil is replaced with coco-peat, rock wool or rocks, plants become highly sensitive to the nutrient solution. pH is the negative logarithm of hydrogen-ion activity, which tells us about how acidic or basic the soil, water or a solution is. It is calculated in logarithmic units and ranges from 0 to 14. Recirculating hydroponic systems absorb the nutrients from the nutrient solution. This results in a deviation of pH levels and requires timely regulation. Ideally, the pH of the nutrient solution must be between ranges of 5.5 to 6. pH probes have an output impedance of $10^{13}\ \Omega$ and produce an analog output. They require some level of signal conditioning, which is obtained through pH modules. Generally, the pH modules available commercially are very expensive. We focus on discussing the design of an affordable pH module, interfacing it with Arduino, NodeMCU and Raspberry Pi boards.
