Hardware
Seeed XIAO ESP32S3 Plus with external antenna — perfect for outdoor placement.
The XIAO ESP32S3 Plus has an external antenna connector (U.FL) for reliable WiFi when the spa is in the backyard. The dual-core architecture dedicates Core 0 to the timing-critical bus protocol while WiFi runs on Core 1.
MCU Board
Seeed XIAO ESP32S3 Plus
Compact (21×17.8mm), USB-C, dual-core Xtensa LX7 at 240MHz. The "Plus" variant includes 16MB flash, 8MB PSRAM, and critically — a U.FL connector for an external antenna. Full ESPHome and Home Assistant support.
Why This Board?
External Antenna
U.FL connector for reliable backyard WiFi
USB-C
Modern connector — no micro USB in 2026
Dual-Core
Isolate protocol timing from WiFi stack
Comparison
| Feature | SuperMini | XIAO S3 Plus | Pico W |
|---|---|---|---|
| External Antenna | No (PCB only) | Yes (U.FL) | No |
| USB Connector | USB-C | USB-C | Micro |
| Flash / PSRAM | 4MB / 512KB | 16MB / 8MB | 2MB / 0 |
| Cores | 2 @ 240MHz | 2 @ 240MHz | 2 @ 133MHz |
| Price | ~$5 | ~$10 | ~$6 |
Why not the cheaper SuperMini? The SuperMini's PCB antenna may struggle with WiFi signal when the spa is in the backyard. The XIAO's external antenna connector ensures reliable connectivity for outdoor installations.
External Antenna
2.4GHz Antenna with U.FL Connector
Get a small 2.4GHz antenna with a U.FL (IPEX) connector. These are ~$2 and dramatically improve WiFi range compared to PCB antennas.
Mount the antenna outside the IP65 enclosure or use an enclosure with an antenna pass-through for best reception.
Level Shifter
BSS138 Bidirectional Level Shifter
The Intex bus runs at 5V TTL. The ESP32-S3 is 3.3V and not 5V tolerant. A BSS138-based level shifter module handles bidirectional translation for DATA, CLK, and HOLD.
Pre-made 4-channel modules cost ~$0.50 on AliExpress. Include pull-up resistors, just connect and go.
Bill of Materials
| Component | Part | Purpose | Price |
|---|---|---|---|
| MCU | Seeed XIAO ESP32S3 Plus | WiFi + U.FL, dual-core 240MHz, USB-C | ~$10 |
| Antenna | 2.4GHz with U.FL connector | Outdoor WiFi range | ~$2 |
| Level Shifter | BSS138 module (4-ch) | 5V ↔ 3.3V for bus signals | ~$0.50 |
| Capacitor | 10µF electrolytic | Power supply filtering | ~$0.10 |
| Wires | Dupont/hookup | To 5-pin connector | ~$0 |
| Enclosure | IP65 box | Weather/splash protection | ~$3 |
Total: ~$16 — The external antenna is worth the extra cost for reliable outdoor operation.
Optional: 3D Printed Connectors
To avoid cutting the control panel cable, you can 3D print compatible connectors:
- Intex PureSpa connectors by Psykokwak
- Full case with connectors (adaptable for XIAO)