Hardware Guide

Overview

This guide walks you through building the Pool Controller hardware — from selecting parts to final assembly. Even if you’ve never soldered before, the step-by-step instructions will help you get it right.

Target audience: DIY electronics enthusiasts with basic soldering experience. Total cost: under 100€ (excluding pumps and pool infrastructure).

Safety First ⚠️

• The controller switches 230V AC mains voltage to the pumps. Improper wiring poses risk of electric shock or fire.
• Only work on the circuit when disconnected from power.
• Use a residual-current device (RCD) for the pump circuit.
• Keep sensor wiring (low voltage) physically separate from mains wiring.
• If in doubt, consult a qualified electrician for the mains connection.

Required Parts (BOM)

Where to Buy

All parts are widely available on Amazon, AliExpress, eBay, or at electronics distributors like Reichelt, Pollin, Conrad (DE/AT/CH).

• ESP32: Search for “ESP32 DevKit V1” or “ESP32 NodeMCU-32S”. Avoid ESP32-S2/S3/C3 variants unless you adapt the firmware — the project targets standard ESP32 (Xtensa dual-core).
• DS18B20: Look for stainless steel, waterproof probes with 1m cable. Cheaper plastic-encapsulated sensors work too but are less durable outdoors.
• Relay Module: Read the module specification carefully. The firmware uses active-high logic (GPIO HIGH → relay ON). Many cheap modules are active-low with a jumper to switch. Check the documentation or use a jumper wire to verify before wiring permanently.
• Resistors: Any 4.7kΩ ±5% resistor works. Buy a 100-pack for < 3€.

Pin Assignment (Firmware Defaults)

The firmware uses an optimized pin assignment that avoids strapping pins and ADC2-related issues (see Alternative Pin Assignment for details). Defined in src/Config.hpp:

Note: These pins are chosen for maximum compatibility. GPIO15/16/18/19 (the original assignment) work for most users, but the optimized pins eliminate any boot-strapping risk and avoid ADC2 pins entirely — see Alternative Pin Assignment for the original layout.

Wiring Diagram

 ─── POWER SUPPLY ──────────────────────────────────────────────────

  [USB PSU 5V/1A+]           [ESP32 Board]           [Relay Module]
   ┌──────────┐              ┌─────────────┐          ┌────────────┐
   │ 5V (+) ──┼──────────────┤ VIN         │          │ VCC        │
   │          │              │  (powers    │      ┌───┤ (powers    │
   │          │              │   board)    │      │   │  coils)    │
   │          │              │             │      │   │            │
   │          │              │ 3V3 ───┬────┘      │   │ GND ◄──────┼──┐
   │          │              │        │           │   └────────────┘  │
   │ GND ─────┼──────────────┤ GND ◄──┼───────────┼──────────────────┘
   └──────────┘              └────────┘           │

 ─── SENSORS ──────────────────────────────────────────────────────

  [DS18B20 Solar]                               [DS18B20 Pool]
   ┌───────────┐                                 ┌───────────┐
   │ VDD (red) ─┼── 3.3V ─────────────────────────┼── VDD (red)│
   │           │                                 │           │
   │ GND (blk) ─┼── GND ──────────────────────────┼── GND (blk)│
   │           │                                 │           │
   │DATA (yel) ─┼── GPIO32 (PIN_DS_SOLAR)         │           │
   │           │  │                              │           │
   │           │  └──[4.7kΩ]── 3.3V ← pull-up    │           │
   │           │                   resistor      │           │
   │           │                                 │DATA (yel) ─┼── GPIO33 (PIN_DS_POOL)
   │           │                                 │           │  │
   │           │                                 │           │  └──[4.7kΩ]── 3.3V
   └───────────┘                                 └───────────┘

 ─── RELAY CONTROL SIGNALS ────────────────────────────────────────

  ESP32 GPIO25 ────────────────────────────────── Relay IN1 (Pool)
  ESP32 GPIO26 ────────────────────────────────── Relay IN2 (Solar)

 ─── STATUS INDICATION ────────────────────────────────────────────

  ESP32 Built-in LED (GPIO2) ── Status blink codes (Homie)

 ─── RELAY LOAD SIDE (230V AC) ────────────────────────────────────

  L (mains) ─── RCD ─── MCB ──┬── Relay COM1 ── Pool Pump
                               └── Relay COM2 ── Solar Pump
  N (neutral) ───────────────────────── Neutral bar ── Pump N

Wire Connections (Step by Step)

1. Temperature Sensors (DS18B20)

The DS18B20 has three wires (on waterproof probes: typically red = VDD, yellow/white = DATA, black = GND — but verify with your sensor’s datasheet):

Critical — add the 4.7kΩ pull-up resistor:

Each sensor DATA line must have a 4.7kΩ resistor connecting it to 3.3V. Without it, the sensor will not be detected.

   Solar DATA ──── 4.7kΩ ──── 3.3V
   Pool  DATA ──── 4.7kΩ ──── 3.3V

Solder the resistor as close to the ESP32 pin header as possible, connecting between the DATA pin and the 3.3V rail. The resistor can be any 4.7kΩ ±5% (¼W or ⅛W, metal film or carbon film).

2. Relay Module

Important — Logic Level: The firmware sets the GPIO pin HIGH (3.3V) to activate (close) the relay. If your relay module switches with LOW instead (active-low), look for a jumper on the module to change the mode, or choose a different module — active-high modules are easier to work with.

Load wiring (230V side):

   L (mains live) ─── RCD ─── MCB ──┬── Relay COM1 ── Pool Pump
                                     │       NO1 ─────┘
                                     │
                                     └── Relay COM2 ── Solar Pump
                                             NO2 ─────┘
   N (neutral) ───────────────────────── Neutral bar ── Pump N

• Connect the pump’s live wire to the relay’s COM (common) terminal.
• Connect the relay’s NO (normally open) terminal to the pump.
• The other pump wire goes to neutral (N).
• Always wire the 230V circuit through an RCD and appropriately rated MCB.

3. Power Supply

Important: The ESP32’s on-board 3.3V regulator can supply ~600mA. The DS18B20 sensors draw < 5mA total — well within limits. If you add many additional 3.3V components, consider an external 3.3V regulator.

Step-by-Step Assembly

Prototyping on a Breadboard

1. Place the ESP32 on the breadboard straddling the center gap
2. Connect power rails: 3.3V and GND rails on both sides
3. Insert the 4.7kΩ resistors: Between the DATA row and 3.3V rail
4. Connect DS18B20 sensors: Use jumper wires for VDD (3.3V), GND, and DATA
5. Connect the relay module: Jumper wires for VCC (5V), GND, IN1, IN2
6. Power via USB: The ESP32’s VIN/USB pin provides 5V for the relay module
7. Double-check all connections before applying power
8. Verify: See First Power-On below

💡 Tip: Use different colored jumper wires for clarity — e.g., red for power (3.3V/5V), black for GND, yellow for sensor data, blue for relay control.

Permanent Assembly on Perfboard

Once you’ve verified the circuit on a breadboard, build the permanent version:

1. Plan the layout: Arrange components on the perfboard before soldering. Keep the 230V relay terminals at one edge, sensors at the opposite edge.
2. Solder in this order:
   • Pin headers / screw terminals for the ESP32 (socket it, don’t solder directly)
   • Resistors (4.7kΩ)
   • Pin headers for the relay module (socket it too)
   • Screw terminals for sensor connections
3. Wire routing: Use solid core wire for connections. Keep data lines short.
4. Inspect for solder bridges: Check each joint with a magnifier or multimeter (continuity test).
5. Mount in enclosure: Use standoffs or double-sided foam tape. Drill holes for sensor and relay cable entries. Use cable glands (PG7/PG9) for a water-resistant seal.

Manufacturing Tips

Soldering

• Use leaded solder (Sn60Pb40 or Sn63Pb37) for easiest handling — it flows better than lead-free, especially for beginners.
• Flux: Use rosin-core solder; add liquid flux for stubborn joints.
• Temperature: Set iron to 320–350°C for leaded, 370–400°C for lead-free.
• Iron tip: Clean with a wet sponge or brass wool before every joint.
• Good joint: Shiny, concave fillet that flows around the component lead. A dull, cracked, or ball-shaped joint is bad — reheat and add fresh solder.

Enclosure

• Choose an ABS or PVC project box with at least IP54 rating for outdoor installation (splash protection).
• Drill ventilation holes if the relay module gets warm, but angle them downwards to reduce water ingress.
• Mount the ESP32 on M2.5 or M3 nylon standoffs to avoid short circuits.
• Label external connectors (pool sensor, solar sensor, pump 1, pump 2, USB power).
• Use cable glands (PG7 for thin sensor cables, PG9 for thicker power cables) where wires enter the enclosure.

Cable Management

• Label both ends of each wire with heat-shrink wrap or small adhesive labels — future-you will thank past-you.
• Keep sensor and relay wires separate inside the enclosure to minimize electrical noise coupling.
• Strain relief: Tie internal wires to mounting posts or use cable ties so that pulling on external cables doesn’t stress solder joints.
• Service loop: Leave enough slack inside the enclosure so you can open it and work without disconnecting everything.

Outdoor Sensor Installation

• DS18B20 probes are waterproof but the cable entry at the sensor end is not always fully sealed. Apply heat-shrink tubing over the cable joint or use self-amalgamating silicone tape for outdoor installations.
• Route sensor cables in conduit (PVC or flexible) where they are exposed to mechanical stress (lawn, pavement).
• Max cable length: DS18B20 works reliably up to ~30m with a 4.7kΩ pull-up and twisted-pair cable. For longer runs, reduce the pull-up to 2.2kΩ or use a dedicated OneWire driver.
• Position the pool sensor in the pump circuit (after the filter, before the pump return) for accurate average pool temperature.
• Position the solar sensor at the hottest point of the solar collector (usually the top outlet pipe).

Power Supply Options

Recommendation: If you’re installing in a permanent location near your pump control panel, use a DIN-rail 5V PSU (e.g., Mean Well HDR-15-5). It’s clean, reliable, and can power both the ESP32 and the relay module without issue.

Alternative — Industrial controller: The NORVI IIOT-AE01-R is an ESP32-based industrial controller with built-in relays, 24V DC supply, DIN-rail mount, and CE certification. If you already have a 230V AC → 24V DC power supply, no additional 5V PSU is needed. See the NORVI AE01-R Configuration Guide for details.

First Power-On and Testing

1. Visual Inspection

Before connecting power:

• Check for solder bridges between adjacent pins
• Verify polarity of all components (DS18B20 VDD/GND, relay VCC/GND)
• Ensure no stray wire strands are shorting neighboring pins
• Measure resistance between 3.3V and GND — should be > 10kΩ (not shorted)

2. Power On

1. Connect USB power (or 5V PSU)
2. The ESP32’s built-in LED follows the LED Status Codes:
   • Fast blink (5 Hz) — AP mode (no WiFi configured welcome page active)
   • Slow blink (1 Hz) — WiFi connecting
   • Mostly on, brief blink every 2s — WiFi connected, MQTT disconnected
   • Solid on — WiFi + MQTT fully connected

3. Verify Sensors

Open the serial monitor (115200 baud):

Pool Controller v3.3.0
Starting up...
✓ Pin configuration validated - no conflicts (optimierte Belegung)
  Solar Temp (DS18B20): GPIO32
  Pool Temp  (DS18B20): GPIO33
  Pool Pump  (Relay):   GPIO25
  Solar Pump (Relay):   GPIO26
  Status LED:           GPIO2 (LED_BUILTIN)

If sensors are connected and working:

Solar temperature: 25.3°C
Pool temperature:  22.1°C

If you see Sensor error or -127°C, check:

• 4.7kΩ pull-up resistor present on each DATA line?
• DS18B20 VDD connected to 3.3V (not 5V)?
• DS18B20 GND connected to common ground?
• DATA pin matches the firmware configuration?

4. Test Relays

From the Web UI (Configuration tab) or via serial command:

Mode: manual
Pool pump: ON  → relay should click, pump starts
Solar pump: ON → relay should click, pump starts

If relay doesn’t click:

• Is the relay module powered (5V between VCC and GND)?
• Is the logic level correct (active-high vs active-low)?
• Does the LED on the relay module light up when GPIO goes HIGH?

Troubleshooting

Alternative Pin Assignment (Original)

The firmware now uses the optimized pins (GPIO32/33/25/26) by default, as shown in the Pin Assignment table above. The original assignment (GPIO15/16/18/19) is available if you need to share pins with legacy shield boards or other hardware — simply edit src/Config.hpp:

constexpr uint8_t PIN_DS_SOLAR{15};     // was 32
constexpr uint8_t PIN_DS_POOL{16};      // was 33
constexpr uint8_t PIN_RELAY_POOL{18};   // was 25
constexpr uint8_t PIN_RELAY_SOLAR{19};  // was 26

The optimization is analyzed in detail in the ESP32 Schematic Optimization document (German).

LED Status Codes (Homie Convention)

The controller uses its built-in LED to signal the current system state, following the Homie Convention standard for IoT device status indication. The LED is updated once per control loop cycle.

LED Pattern	System State	Visual
Rapid blink (100ms on/off = 5 Hz)	AP Mode — no WiFi configured, setup captive portal active
Slow blink (500ms on/off = 1 Hz)	Connecting — WiFi connection in progress
Mostly on, brief blink every 2s	WiFi OK, MQTT disconnected — network up, broker not reachable
Solid on	Fully connected — WiFi + MQTT operational
Very fast blink (50ms on/off = 10 Hz)	OTA Update — firmware download/install in progress
Double blink (200/200/200/600ms)	Safe Mode — boot-loop detected or critical degradation

What to expect at first power-on:

1. Fast blink — AP mode (no WiFi configured yet)
2. After configuring WiFi via the web portal → slow blink while connecting
3. Once connected → mostly on while MQTT connects
4. Solid on — everything is running normally

Tip: If the LED stays in fast blink after power-on, open the Pool-Controller-Setup WiFi network to configure your home WiFi.

References

• Fritzing source file: pool-controller.fzz
• KiCad Schematic: ESP32 Dev Board — KiCad 9.0 PDF export
• KiCad Schematic: NORVI AE01-R — KiCad 9.0 PDF export
• NORVI AE01-R Configuration Guide — industrial ESP32 controller pin mapping & wiring
• ESP32 Schematic Optimization (DE)
• ESP32 Complete Wiring Schematic (DE)
• DS18B20 Datasheet
• ESP32 Pin Reference
• Config.hpp pin source