Hardware Guide of Pool Monitor

Overview

The Pool Monitor is a ready-to-use display device built around the LILYGO TTGO T5 e-paper ESP32 board family. Unlike the Pool Controller, no additional sensors or relay modules are required — just the board itself.

Target audience: Anyone comfortable with basic electronics (connecting USB power). No soldering required.

Total cost: ~35–55€.

Safety ⚠️

• The Pool Monitor itself operates at low voltage (5V USB) only.
• However, it reads data from the Pool Controller which switches 230V AC mains voltage. The monitor only receives MQTT data — it does not directly handle mains voltage.
• Keep the USB cable and board in a dry location. If used outdoors, place it in a weatherproof enclosure (IP54 or better).

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).

• TTGO T5: Search for “TTGO T5 V2.3.1 e-paper ESP32” or “LILYGO T5 e-ink display”. Make sure to get the V2.3.1 revision for the newest E-Ink panel.
• USB-C cable: Any data-capable cable works. Avoid charge-only cables for firmware flashing.
• Power supply: Standard USB phone charger (5V/≥1A). The board draws very little power, but a quality supply prevents brownouts during WiFi operation.

Compatible Board Variants

The TTGO T5 series comes in multiple revisions. The firmware supports:

To select a different variant, edit src/board_def.h and set the corresponding define at the top of the file:

#define LILYGO_T5_V231 1   // default — comment this out for other variants
// #define TTGO_T5_2_1  1  // example: uncomment for 2.9" variant

Then rebuild the firmware (see Software Guide).

Pin Assignment

The pin configuration is defined in src/board_def.h and varies by board variant. For the default V2.3.1 (V231) board:

The SPI pins are shared with the ESP32’s flash memory — this is normal and works because the E-Ink display is only accessed when the CPU is idle.

Pinout Notes

• SPI MISO is unused because the E-Ink display receives data only (no read-back needed).
• GPIO23 is dual-purpose (SPI MOSI + MODEM_POWER_ON). In deep sleep it is driven LOW to turn off external modem power. During normal operation both functions coexist safely.
• The strapping pins (GPIO0, GPIO2, GPIO12, GPIO15) are avoided for E-Ink control signals to prevent boot issues.

Wiring

No manual wiring is required. The TTGO T5 board integrates all components:

• ESP32 microcontroller (dual-core Xtensa LX6)
• 2.13" E-Ink display (SPI-connected, GxDEPG0213BN panel)
• USB-to-serial converter (CP210x or CH340)
• 3.3V voltage regulator
• Battery charging circuitry (optional Li-Po connector)

Simply connect the board via USB-C:

• To a computer for flashing the firmware
• To a USB phone charger for permanent operation

Buttons (on supported variants)

Some TTGO T5 variants include hardware buttons. The firmware currently does not use them — all configuration is done via the captive portal (see Users Guide).

Power Supply

Power Consumption

The 180-second deep sleep cycle means the board spends >90% of its life in deep sleep, making it suitable for battery operation with a suitably sized Li-Po cell (the TTGO T5 has a built-in battery connector and charger).

Solar Power Operation ☀️

The Pool Monitor’s extremely low power consumption (average ~5.5 mA at 5 V) makes it an excellent candidate for autonomous solar operation. With a small solar panel and a Li‑Po battery, the device can run indefinitely without a USB power supply.

Prerequisite: The TTGO T5 board includes a built-in Li‑Po charger (TP4056) and a JST 1.25 mm battery connector. For solar operation you only need a solar panel and a battery — the board handles charging electronics itself.

Power Budget

The daily energy requirement of ~130 mAh (at 5 V) can be met by even a small solar panel at most locations.

Additional Parts Required

Where to Buy Solar Components

• Solar panel: Search for “5V 2W solar panel” or “6V 200mA solar module”, e.g. on Amazon, AliExpress. Monocrystalline panels with ETFE coating are ideal for outdoor use.
• Li‑Po battery: Search for “3.7V 1000mAh Li‑Po JST 1.25” or “LP401230 1000mAh”. Make sure it has a 1.25 mm JST connector (2‑pin). Common form factors: 401230 (1000 mAh, ~30×12×4 mm) or 503048 (1500 mAh).
• USB‑C breakout: For direct 5 V injection via the USB‑C port.

Circuit Variants

Variant A: Solar Panel → USB‑C (recommended, simple)

The simplest and safest method — uses the built-in TP4056 charger of the TTGO T5.

  Solar Panel          TTGO T5 V231
  (5-6V)                  ┌────────┐
     │                    │ USB-C  │
     ├─[USB-C Breakout]───┤  Port  │
     │                    │        │
  Li‑Po Battery           │  JST   │
  (3.7V, 1000mAh) ────────┤  BAT   │
                           └────────┘

1. Solar panel (5–6 V) — solder to a USB‑C breakout board or directly to a USB‑C plug (VBUS to pins A4/A9/B4/B9, GND to A1/B1).
2. Plug the USB‑C breakout into the TTGO T5’s USB‑C port.
3. Li‑Po battery — connect to the JST 1.25 mm (BAT) connector on the TTGO T5.

Note: The panel must deliver 5 V (nominal) up to 6 V max. The TP4056 requires at least ~4.5 V to start charging.

Variant B: External Solar Charger (more flexible)

Uses a dedicated solar charger module (e.g. CN3065 or TP4056 with solar input) for better energy harvesting in low light.

  Solar Panel        Solar Charger        TTGO T5 V231
  (5-6V)             Module               ┌────────┐
     │                  │                  │ USB-C  │
     ├──────────────────┤ IN+         OUT+─┤  Port  │
     │                  │                  │        │
                         │ BAT+  ────────   │  JST   │
  Li‑Po Battery ────────┤ BAT-      ──────┤  BAT   │
                         │                  └────────┘

1. Connect solar panel to the IN+ / IN− terminals of the charger module.
2. Connect Li‑Po battery to BAT+ / BAT− of the charger.
3. Connect charger output to the TTGO T5’s JST BAT connector or via a 5 V step-up converter to the USB‑C port.

Advantage: Modules like the CN3065 feature an MPPT‑like input regulator that still harvests power in cloudy conditions.

Minimum Configuration (Summer Only) ☀️

If the monitor only needs to run during the warm season (May–September) in mostly good weather, minimal components are sufficient:

The daily requirement of ~130 mAh is already exceeded by a 0.3 W panel (60 mA × 6 h × 0.7 efficiency ≈ 250 mAh/day) in summer. The battery handles the night – even after a cloudy day there’s enough reserve for the next day.

Practical tip: A panel below 0.5 W is often barely cheaper than a 0.5 W panel. Recommendation: 0.5 W + 500 mAh battery as the cheapest combination (~15–25 € additional to the board).

Sizing

Battery Capacity

Rule of thumb: In central Europe (DE/AT/CH) winter months typically see 2–3 effective sun hours per day (Nov–Feb). A 1000 mAh battery bridges 5–7 days without sun. A 2000 mAh battery lasts 10–14 days.

Solar Panel Size

Recommendation:

• Summer only: 0.5 W + 500 mAh battery – small, light, cheap
• Year-round (DE/AT/CH): 1–2 W + 1000–2000 mAh battery

Panel Dimensions (approximate)

Wiring – Step by Step

Preparation

1. Disconnect TTGO T5 from any power source (USB‑C and battery).
2. Lay out all components on a non-conductive surface.
3. If using stranded wire: tin the ends, prepare heatshrink tubing.

Variant A (recommended) – Step by Step

1. Prepare the USB‑C breakout: Tin the VBUS and GND pads with a fine soldering iron.
2. Prepare the solar panel: Insulate the panel leads with heatshrink; positive (red) to VBUS, negative (black) to GND on the breakout.
3. Optional: Schottky diode 1N5819 — place in series with the positive lead (cathode toward breakout, anode toward panel) to prevent reverse current at night.
4. Insert the breakout: Gently plug the USB‑C breakout into the TTGO T5’s USB‑C port.
5. Connect the Li‑Po battery: Plug the battery connector into the JST 1.25 mm (BAT) socket on the TTGO T5. Watch polarity — red wire = positive.
6. Visual inspection: No loose wires, no short circuits.

Test

1. Connect solar panel only (no battery) — the red LED on the TTGO T5 should light if the panel receives sufficient light. The board should boot.
2. Disconnect panel, connect battery only — the board should boot from battery.
3. Connect both — normal operation. The TP4056 charges the battery in sunlight and automatically switches to battery when dark.
4. Test the firmware: WiFi connection, MQTT, display update.

Enclosure and Placement

• Use a weatherproof enclosure (IP65+), e.g. ABS plastic enclosures from Bopla, Spelsberg, or Hammond.
• The solar panel can either:
  • be mounted on the outside of the enclosure (cable routed through a cable gland),
  • or be placed inside behind a clear window if the lid is transparent (yield reduction ~10–20 %).
• Placement: South-facing, tilt 30–45°, no shading (trees/buildings). In DE/AT/CH, as little as 2–3 h of midday sun is enough for minimum operation.
• Ventilation slots are not required due to the low heat dissipation.
• Temperatures: The Li‑Po battery should not exceed 60 °C. In direct sunlight on a dark enclosure, avoid heat buildup (use a light-colored enclosure or place in partial shade).

Notes and Safety ⚠️

• Li‑Po safety: Only use batteries with built-in overcharge/overdischarge protection (PCB). Replace immediately if damaged (swelling, bulging).
• Never connect the solar panel to the JST BAT socket — that connector is for the battery only. The TP4056 input is limited to 6 V max; higher voltage will destroy the charger.
• USB‑C data path: Variant A occupies the USB‑C port. To flash new firmware, unplug the breakout — unless you use UART via the pin headers (RX/TX) on the board.
• Strain relief: Use cable ties or glue dots inside the enclosure to prevent force on the connectors.

First Power-On and Testing

1. Visual Inspection

Before connecting power:

• Check the USB-C connector for debris
• Verify the board is not placed on a conductive surface
• Look for any visible damage (swollen components, corrosion)

2. Power On

1. Connect the TTGO T5 to a USB power source (computer or phone charger).
2. The E-Ink display will update after a few seconds:
   • With stock firmware: a test pattern or blank screen.
   • With Pool Monitor firmware: the splash screen — see Users Guide for first-time configuration.

3. Initial Configuration

The device starts in AP mode if no WiFi is configured:

1. Connect your phone/laptop to the pool-monitor WiFi network (open, no password).
2. A captive portal opens automatically — or navigate to http://192.168.4.1.
3. Enter your WiFi credentials and MQTT broker settings.
4. Click Save — the device reboots and connects to your network.

Details in the Users Guide.

Troubleshooting

References

• LILYGO TTGO T5 Product Page
• GxEPD Library
• ESP32 Datasheet
• Pool Controller Hardware Guide
• Board definition source