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 these GPIO pins (defined in src/Config.hpp):

Note on GPIO15: This pin is a Strapping pin on the ESP32 — it affects the boot process if pulled HIGH or LOW at startup. The firmware works reliably with it here, but if you experience boot issues, consider moving the DS18B20 sensors to GPIO32/33 and updating src/Config.hpp accordingly (see the Wiring Optimization section).

Wiring Diagram

                         +-------------------------+
                         |         ESP32           |
                         |                         |
  DS18B20 SOLAR DATA --->| GPIO15   (PIN_DS_SOLAR) |
  DS18B20 POOL  DATA --->| GPIO16   (PIN_DS_POOL)  |
  Relay IN1 (Pool)  ---->| GPIO18   (PIN_RELAY_POOL)|
  Relay IN2 (Solar) ---->| GPIO19   (PIN_RELAY_SOLAR)|
                         |                         |
  3.3V ------------------>| 3V3                     |
  GND ------------------->| GND                     |
                         +-----------+-------------+
                                     |
                                     | common GND
                                     v
         +--------+--------+--------+--------+
         |        |        |        |        |
    +----+--+  +--+----+  |   +----+--+  +--+----+
    |Solar  |  | Pool  |  |   | RLY1  |  | RLY2  |
    |DS18B20|  |DS18B20|  |   |(Pool) |  |(Solar)|
    |       |  |       |  |   |       |  |       |
    | VDD --+--+ VDD --+--+---> 3.3V  |  |       |
    | GND --+--+ GND --+-------> GND  |  |       |
    |DATA --->| GPIO15|  |   |       |  |       |
    |       |  |DATA -->|  |   | VCC  |  | VCC  |
    +-------+  +-------+  |   | -- 5V |  | -- 5V|
                           |   | GND  |  | GND  |
                           |   |      |  |      |
                    4.7kΩ  |   | IN1  |  | IN2  |
                     |     |   | <-18 |  | <-19 |
                     v     |   +------+  +------+
                3.3V ----+-+--- 3.3V

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 pull-up resistor:

Connect a 4.7kΩ resistor between the DATA wire and the 3.3V line. One resistor per sensor, as close to the sensor wire connection as possible.

    ESP32 3.3V ──┬── 4.7kΩ ──── DS18B20 DATA
                  │
                DS18B20 VDD

Without this resistor, the sensor will not be detected — this is the #1 cause of “no sensor found” errors.

2. Relay Module

Relay Logic: The firmware sets the GPIO pin HIGH (3.3V) to activate the relay. If your module switches with LOW (active-low), flip the jumper or adapt the firmware (see src/RelayModuleNode.cpp).

Load wiring (230V side):

    L ──┤ RCD ├──┤ MCB ├──┬──┤ Relay-COM1 ├── Pool Pump ── N
                           └──┤ Relay-COM2 ├── Solar 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.

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 should flash quickly (boot sequence)
3. After ~3 seconds, the LED blinks slowly — waiting for WiFi

3. Verify Sensors

Open the serial monitor (9600 baud):

Pool Controller v3.3.0
Starting up...
Initialized pins: GPIO15, GPIO16, GPIO18, GPIO19
Solar Temp: GPIO15
Pool Temp:  GPIO16
Pool Relay: GPIO18
Solar Relay: GPIO19

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

Optional: Wiring Optimization

The default pins (GPIO15/16/18/19) work reliably for most users. If you experience boot instability or want the most robust configuration, use these optimized pins instead:

To use optimized pins, edit src/Config.hpp:

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

This pinout is already analyzed and recommended in the ESP32 Schematic Optimization document (German).

References

• Fritzing source file: pool-controller.fzz
• ESP32 Schematic Optimization (DE)
• ESP32 Complete Wiring Schematic (DE)
• DS18B20 Datasheet
• ESP32 Pin Reference
• Config.hpp pin source