Hardware Guide | Water Quality Monitor

This guide provides comprehensive information for building the Water Quality Monitor hardware, from selecting parts to assembling the complete device.

⚠️ Status: Under Development — This module is in the planning phase. Hardware specifications may change as development progresses.

✨ Overview

The Water Quality Monitor is designed to be a modular, extensible device for monitoring swimming pool water chemistry. The current design focuses on pH and chlorine monitoring, with the ability to add additional sensors in the future.

Design Goals:

• Accuracy: Reliable measurements comparable to commercial test kits
• Reliability: Robust operation in outdoor pool environments
• Extensibility: Easy to add new sensor types
• Affordability: Cost-effective compared to commercial systems
• Integration: Seamless integration with Smart Swimming Pool ecosystem

⚡ Parts List (BOM)

⚡ Core Components

⚡ Optional Components

⚡ Enclosure & Installation

⚡ Tools Required

⚡ Total Cost Estimate

⚡ Sensor Selection Guide

⚡ pH Sensors

We recommend the following pH sensors based on testing and community feedback:

✅ Recommended: 14core pH Sensor with BNC Probe

Specifications:

• Range: 0-14 pH
• Resolution: 0.01 pH
• Accuracy: ±0.1 pH
• Response Time: < 1 minute
• Temperature Range: 0-60°C
• Output: Analog voltage (0-3.3V or 0-5V)
• Connector: BNC
• Probe Type: Glass electrode with reference

Pros:

• Affordable price
• BNC connector for easy replacement
• Good documentation and support
• Compatible with ESP8266 ADC

Cons:

• Requires regular calibration
• Limited lifespan (1-2 years)
• Sensitive to temperature changes

Resources:

• Product Page
• Datasheet
• Wiring Guide

⚡ Alternative: Atlas Scientific pH Sensor

Specifications:

• Range: 0-14 pH
• Resolution: 0.001 pH
• Accuracy: ±0.01 pH
• Interface: I2C or UART
• Probe Type: Industrial glass electrode

Pros:

• Very high accuracy
• Digital interface (less noise)
• Robust construction
• Long lifespan

Cons:

• Expensive
• Requires specific circuit design

Resources:

• Atlas Scientific pH Sensor
• I2C pH Circuit

⚡ Alternative: DFRobot pH Sensor

Specifications:

• Range: 0-14 pH
• Resolution: 0.1 pH
• Accuracy: ±0.1 pH
• Output: Analog voltage
• Interface: Gravity 3-pin connector

Pros:

• Good documentation
• Easy to use with Arduino/ESP8266
• Affordable

Cons:

• Lower accuracy than Atlas Scientific
• Requires calibration

Resources:

• DFRobot pH Sensor
• Wiki

⚡ Chlorine Sensors

Chlorine sensor selection depends on your requirements and budget:

⚡ Option 1: Electrochemical Chlorine Sensor

Specifications:

• Range: 0-10 ppm (free chlorine)
• Resolution: 0.1 ppm
• Accuracy: ±0.5 ppm
• Response Time: < 2 minutes
• Interface: Analog voltage
• Lifespan: 1-2 years

Pros:

• Direct measurement
• Real-time monitoring
• Good accuracy

Cons:

• Requires regular calibration
• Limited lifespan
• Sensitive to temperature and pH

Note: Many electrochemical chlorine sensors require specific calibration procedures and may have cross-sensitivity to other chemicals.

⚡ Option 2: Optical Chlorine Sensor

Specifications:

• Range: 0-10 ppm
• Resolution: 0.1 ppm
• Accuracy: ±0.2 ppm
• Interface: I2C or UART
• Lifespan: 2-5 years

Pros:

• No calibration needed (factory calibrated)
• Long lifespan
• Less sensitive to interference

Cons:

• Expensive
• Complex optical design
• May require specific light sources

⚡ Option 3: DPD Colorimetric Method

Specifications:

• Range: 0-10 ppm
• Resolution: 0.1 ppm
• Accuracy: ±0.2 ppm
• Interface: Analog (color intensity)
• Method: Chemical reaction with DPD reagent

Pros:

• Standard method used in test kits
• Good accuracy
• Well understood chemistry

Cons:

• Requires reagent tablets or powder
• Manual process (unless automated)
• Reagents have limited shelf life

Note: DPD method can be automated with a peristaltic pump and colorimeter, but this adds significant complexity.

⚡ Temperature Sensor (Optional)

Recommended: DS18B20 Waterproof Temperature Sensor

Specifications:

• Range: -55°C to +125°C
• Accuracy: ±0.5°C
• Resolution: 9-12 bits (configurable)
• Interface: OneWire
• Waterproof: Yes (stainless steel probe)
• Cable Length: 1m (standard)

Pros:

• Affordable
• Waterproof
• Easy to use with ESP8266
• No calibration needed

Cons:

• Requires pull-up resistor
• Limited to 12 sensors per OneWire bus

Resources:

• DS18B20 Datasheet
• Waterproof DS18B20

⚡ Circuit Design

⚡ Basic Circuit (pH Only)

This is the simplest configuration for pH monitoring only.

ESP8266 Development Board (WeMos D1 Mini)
   
   3.3V [ pH Sensor VCC ]
   GND [ pH Sensor GND ]
   A0  [ pH Sensor Output ]
   
   pH Sensor Board (14core)
   
   BNC Connector [ pH Electrode Probe ]

Wiring Details:

Important Notes:

• Use 3.3V power, not 5V (most pH sensors are 3.3V compatible)
• Keep wire lengths as short as possible to minimize noise
• Use shielded cable for the analog signal if possible
• Avoid running sensor cables parallel to power cables

⚡ Advanced Circuit (pH + Temperature)

This configuration adds temperature monitoring for pH compensation.

ESP8266 Development Board (WeMos D1 Mini)
   
   3.3V [ pH Sensor VCC ]
   3.3V [ DS18B20 VCC ] (via 4.7kΩ pull-up)
   GND [ pH Sensor GND ]
   GND [ DS18B20 GND ]
   A0  [ pH Sensor Output ]
   D2  [ DS18B20 DATA ] (OneWire)
   
   pH Sensor Board
   
   BNC Connector [ pH Electrode Probe ]
   
   DS18B20 Waterproof Sensor

Wiring Details:

DS18B20 Pull-up Resistor:

• Value: 4.7kΩ
• Connection: Between DS18B20 DATA line and 3.3V
• Important: Required for OneWire communication

⚡ Complete Circuit (pH + Chlorine + Temperature + ADC)

This configuration adds chlorine monitoring and uses an external ADC for better precision.

ESP8266 Development Board (WeMos D1 Mini)
   
   3.3V [ pH Sensor VCC ]
   3.3V [ Chlorine Sensor VCC ]
   3.3V [ ADS1115 VCC ]
   3.3V [ DS18B20 VCC ] (via 4.7kΩ pull-up)
   GND [ pH Sensor GND ]
   GND [ Chlorine Sensor GND ]
   GND [ ADS1115 GND ]
   GND [ DS18B20 GND ]
   
   SDA (D2) [ ADS1115 SDA ]
   SCL (D1) [ ADS1115 SCL ]
   
   ADS1115 Channel 0 [ pH Sensor Output ]
   ADS1115 Channel 1 [ Chlorine Sensor Output ]
   
   D4 [ DS18B20 DATA ] (OneWire)
   
   pH Sensor Board
   BNC Connector [ pH Electrode Probe ]
   
   Chlorine Sensor
   
   DS18B20 Waterproof Sensor

Wiring Details:

ADS1115 Connections:

• A0 → pH Sensor Output
• A1 → Chlorine Sensor Output
• A2, A3 → Available for future sensors

Benefits of External ADC:

• 16-bit resolution (vs 10-bit on ESP8266)
• Programmable gain (1x, 2x, 4x, 8x, 16x)
• Differential inputs for better noise rejection
• Multiple channels for multiple sensors

⚡ Pin Assignment (WeMos D1 Mini)

Note: I2C is a shared bus, so multiple I2C devices (ADS1115, OLED, Atlas Scientific sensors) can share the same SDA/SCL pins.

⚡ Pinout Diagrams

WeMos D1 Mini:

ESP-12E/12F:

⚡ Assembly Instructions

⚡ Step 1: Prepare Components

1. Gather all parts from the BOM
2. Inspect sensors for damage
3. Test pH electrode (if new, it may be dry; soak in storage solution for 24 hours)
4. Prepare tools and workspace

⚡ Step 2: Breadboard Prototyping (Recommended)

Best for: Testing before permanent installation, learning the circuit.

1. Place ESP8266 on breadboard

   • Straddle the center gap
   • Ensure all pins are properly inserted

2. Connect pH sensor

   • Connect VCC to 3.3V rail
   • Connect GND to GND rail
   • Connect Output to A0

3. Add DS18B20 (optional)

   • Connect VCC to 3.3V rail (via 4.7kΩ pull-up resistor)
   • Connect GND to GND rail
   • Connect DATA to D4 (WeMos D1 Mini)

4. Add ADS1115 (optional)

   • Connect VCC to 3.3V rail
   • Connect GND to GND rail
   • Connect SDA to D2
   • Connect SCL to D1
   • Connect pH sensor to A0
   • Connect chlorine sensor to A1

5. Verify connections

   • Use multimeter to check continuity
   • Ensure no short circuits
   • Verify all connections are secure

⚡ Step 3: Test Sensors

1. Test pH sensor:

   • Upload test firmware
   • Calibrate with pH 7.0 solution
   • Test with pH 4.0 and pH 7.0 solutions
   • Verify readings are stable and accurate

2. Test DS18B20 (if installed):

   • Upload test firmware
   • Place sensor in water
   • Verify temperature readings

3. Test ADS1115 (if installed):

   • Upload test firmware
   • Verify analog readings from both channels

⚡ Step 4: Permanent Assembly

Best for: Final installation, outdoor use, long-term operation.

Option A: Perfboard

1. Plan component layout on perfboard
2. Solder ESP8266 with pin headers for easy removal
3. Solder sensor modules with sufficient spacing
4. Add screw terminals for:
   • Power input (3.3V/GND)
   • Sensor connections
5. Solder resistors directly between pins
6. Add test points for debugging

Option B: Custom PCB

For production or multiple units, consider designing a custom PCB:

1. Design schematic using KiCad or Eagle
2. Create PCB layout
3. Order PCB from manufacturer (JLCPCB, PCBWay, etc.)
4. Solder components to PCB
5. Test thoroughly

⚡ Step 5: Enclosure Assembly

1. Prepare enclosure:

   • Drill holes for:
     • Sensor cables (use cable glands)
     • Power input
     • Optional: Display window
   • Add mounting points for PCB/perfboard

2. Install electronics:

   • Mount PCB/perfboard in enclosure
   • Connect sensor cables
   • Add desiccant packs

3. Install sensors:

   • Mount pH electrode in sensor holder
   • Position chlorine sensor (if applicable)
   • Route cables through cable glands

4. Seal enclosure:

   • Ensure all cable glands are tight
   • Check for waterproof integrity
   • Test with water spray (if possible)

⚡ Sensor Installation

⚡ pH Sensor Installation

Location:

• Place sensor in pool water, away from returns and skimmers
• Depth: 30-50 cm below surface
• Avoid placing near pump intakes or heaters
• Ensure good water circulation around sensor

Mounting Options:

1. Floating Mount:

   • Sensor floats on surface
   • Easy to install and remove
   • May be affected by surface debris

2. Wall Mount:

   • Sensor mounted to pool wall
   • Stable position
   • Requires drilling

3. Weighted Base:

   • Sensor rests on pool floor
   • Stable position
   • May collect debris

Cable Routing:

• Use waterproof cable for external installations
• Keep cable runs as short as possible
• Use cable ties for strain relief
• Avoid sharp bends or pinching cables
• Route cables away from pool edges to prevent damage

⚡ Chlorine Sensor Installation (if applicable)

Location: Similar to pH sensor

Considerations:

• May need separate enclosure if using DPD method
• Protect from direct sunlight
• Ensure good water flow around sensor
• Avoid chemical feed points (can cause false readings)

⚡ Temperature Sensor Installation (if applicable)

Location:

• Same location as pH sensor (for temperature compensation)
• Or in return line for average pool temperature

Mounting:

• Use sensor holder or weighted base
• Ensure sensor is fully submerged
• Protect from direct sunlight

⚡ Power Supply

⚡ Power Requirements

⚡ Power Options

⚡ Solar Power Option

For autonomous operation, consider solar power:

Components:

• Solar Panel: 5V/2W (for continuous operation)
• LiPo Battery: 3.7V/2000mAh (for night operation)
• Charge Controller: TP4056 module
• Boost Converter: MT3608 (3.7V to 5V)

Circuit:

Solar Panel (5V) [ TP4056 Charge Controller ]
                                  |
LiPo Battery (3.7V) [ MT3608 Boost Converter ]
                                  |
ESP8266 (5V input) [ AMS1117 3.3V Regulator ]
                                  |
All Sensors (3.3V)

Considerations:

• Panel size: 2W panel provides ~400mA in full sun
• Battery capacity: 2000mAh lasts ~16 hours at 120mA
• Deep sleep: Use deep sleep to extend battery life
• Enclosure: Ensure panel and battery are protected

⚡ Maintenance

⚡ Regular Maintenance Schedule

⚡ pH Sensor Maintenance

Cleaning:

1. Remove sensor from pool
2. Rinse with distilled water
3. Gently clean electrode with soft cloth
4. Soak in storage solution for 1 hour
5. Recalibrate if necessary

Storage:

• Short-term (< 1 week): Store in pH 7.0 buffer solution
• Long-term (> 1 week): Store in storage solution
• Never store dry (will damage electrode)

Troubleshooting:

• Readings unstable: Clean electrode, check for air bubbles
• Readings inaccurate: Recalibrate, check for contamination
• Readings drift: Replace electrode (typically lasts 1-2 years)
• No response: Check connections, verify power

⚡ Chlorine Sensor Maintenance

Maintenance depends on sensor type:

Electrochemical:

• Calibrate monthly or as needed
• Replace annually or when readings become unreliable
• Store dry when not in use

Optical:

• Clean optical window monthly
• Verify calibration quarterly
• Replace every 2-5 years

DPD Colorimetric:

• Replace reagent tablets as needed
• Clean colorimeter window monthly
• Calibrate with known standards

⚡ Troubleshooting

⚡ Common Issues

⚡ Debugging Steps

1. Check power:

   • Verify 3.3V at ESP8266
   • Verify 3.3V at sensors
   • Check for short circuits

2. Check connections:

   • Verify all wires are properly connected
   • Check for cold solder joints
   • Use multimeter to test continuity

3. Test sensors individually:

   • Test pH sensor with known solutions
   • Test DS18B20 with known temperatures
   • Test ADS1115 with simple voltage input

4. Check serial output:

   • Upload debug firmware
   • Monitor serial output for error messages
   • Verify sensor readings in serial monitor

5. Test MQTT:

   • Verify WiFi connection
   • Test MQTT with simple client
   • Check broker logs

⚡ Safety Considerations

⚠️ Electrical Safety

• Use low voltage (3.3V/5V) for all electronics
• Keep electronics dry — Use waterproof enclosures
• Use waterproof connectors for all outdoor connections
• Ground all metal parts if possible
• Use RCD/FI protection for any mains-powered components
• Avoid working on circuit when connected to power

⚠️ Chemical Safety

• Handle calibration solutions with care — Some may be corrosive
• Wear gloves when handling sensors and solutions
• Avoid skin contact with calibration solutions
• Rinse with water if solution contacts skin
• Dispose of old solutions properly — Follow local regulations
• Store chemicals properly — In original containers, labeled

⚠️ Pool Safety

• Do not rely solely on this monitor for pool safety
• Regularly test water manually with test strips or kits
• Follow local health department guidelines for pool water quality
• Keep pool chemicals properly stored and labeled
• Never mix chemicals — Can cause dangerous reactions
• Ensure proper ventilation when handling chemicals

⚡ Additional Resources

⚡ Datasheets

• 14core pH Sensor
• DS18B20 Datasheet
• ADS1115 Datasheet
• ESP8266 Datasheet

⚡ Pinout References

• WeMos D1 Mini Pinout
• ESP-12E Pinout

⚡ External Resources

• 14core pH Sensor Guide
• Atlas Scientific Sensors
• DFRobot Sensors
• SparkFun pH Sensor

Happy building! ✅\n \n Made with ❤️ by the Smart Swimming Pool community