Lecture on pH Sensors

Overview

• Introduction to pH sensors by DFRobot
• Types of pH sensors:
  • Laboratory tests
  • Industrial use
  • Niche sensor with spear tip for wet soil and foods

V2.0 pH Sensors

• Compatible with multiple main controllers (Arduino, ESP32, Raspberry Pi, etc.)
• Power requirement: 3.3V~5V
• Signal adapter: BNC and Gravity interfaces
• Features: Plug and play, no soldering required, hardware-filtered output, low jitter

What is pH?

• Stands for "potential of hydrogen" or "power of hydrogen"
• Scale to specify acidity or basicity of an aqueous solution
• "H" in pH represents hydrogen ions (H+)
• "p" represents the negative logarithm of the quantity

Measuring pH with a pH Sensor

• Based on electrochemical reactions
• Uses Nernst equation to convert hydrogen ion concentration to electric potential

Components of a pH Probe

• Glass bulb with glass membrane sensitive to pH
• Measuring electrode: Thin glass bulb with silver alloy wire in neutral potassium chloride solution
• Reference electrode: Also has a silver alloy wire in neutral potassium chloride solution

Working Principle

• Imbalance of surface charge in solutions leads to membrane potential
• Potential difference determines pH:
  • pH 1: 355mV
  • pH 7: 0mV
  • pH 14: -414mV
• Electrical signal processed by operational amplifier
• Displayed pH value on MCU or PC

Using a pH Meter

• Steps to use:
  1. Connect the pH sensor
  2. Connect to the display
  3. Upload the code
• Result: Simple pH meter
• DFRobot open-source software library for calibration
• Two-point calibration method:
  • Automatically identifies two standard buffer solutions
  • Fast and simple

Practical Examples

• Detecting pH of common liquids:
  • Lemon liquid
  • Milk
  • Soapy water
• Mention of a previous video on calibration
• Potential future video on pH calibration principle if the video gets more than 50 likes