SPM/SDM Open Wi-Fi API Overview

Open Wi-Fi API Overview

Status: Active | Applies to: SPM/SDM Open Wi-Fi Series (ESP32-8685 / C6) | Updated: 2026-07-12

1. Introduction

Our smart energy meters using ESP32 SoCs are designed with an "Open Wi-Fi" philosophy, providing developers and system integrators with a comprehensive suite of local and cloud-based communication protocols.

This section of the documentation is organized into sub-pages detailing specific protocols. Before diving into the specific API references in the left sidebar, please review the firmware compatibility matrix below to ensure your device supports the required features.

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2. Firmware Branches & Hardware Compatibility

The Open Wi-Fi product line currently consists of four main firmware branches.

Firmware Branch	Basic (8685)	Basic+ (8685)	Lite (8685)	Pro (C6)
Target Hardware	SPM / SDM	SDM01	SPM/SDM	SDM01 Gen2
Latest Version	B_5.1.14 & B_6.1.7 1)	BPlus_1.2.8 & BPlus_2.2.4 2)	Lite_5.1.11 & Lite_6.1.42)	Pro_V3.1.11
Core Features	Cleartext BLE & Wi-Fi	Cleartext BLE, Encrypted WiFi 3)	Encrypted BLE & Cleartext WiFi3)	Encrypted BLE & WiFi 3)
WiFi Strength	0 dB	13 dB	0dB	13 dB
Lifecycle Status	NRND	NRND	Active	Active

Note:

1. B_6.1.7 is used for the SDM01 Combo with UART external flashing pin, while B_5.1.14 is used for all other Open WiFi models of SPM01, SPM02, SDM01 Combo with JTAG external flashing pins, and SDM02.

2. BPlus_2.2.4 and Lite_5.1.11 are used for the SDM01 Combo with UART external flashing pin, while BPlus_2.2.4 and Lite_6.1.4 are used for the SDM01 Combo with JTAG external flashing pins.

3. Basic+ was formerly known as the EV/PV version for Gen1, which is replaced by the SDM01 Gen2. It supports a maximum of 1 TLS connection over Wi-Fi (Select 1 out of Modbus TCP, HTTPS, MQTT, and WebSocket).

4. Lite version's BLE encryption covers both provisioning and data broadcasting. Its Wi-Fi only supports TLS 1.2 and 1.3 for MQTT, and no TLS over HTTP, Modbus TCP and Websocket are supported.

5. Pro version's BLE encryption covers both provisioning and data broadcasting. Its Wi-Fi supports up to 2 concurrent TLS connections (Select 2 out of Modbus TCP, HTTPS, MQTT, and WebSocket).

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3. API Capability Matrix

The following matrix details the supported communication protocols across different firmware branches. The primary evolution from Basic/Basic+/Lite to Pro focuses on enhanced security and concurrency.

Firmware Branch	Basic (8685, SPM/SDM)	Basic+ (8685, SDM01)	Lite （8685，SPM/SDM）	Pro (C6, SDM01 Gen2)
BLE Cleartext	✅	✅	❌	❌
BLE Secured	❌	❌	✅	✅
MQTT (Port 1883)	✅	✅	✅	✅
MQTTS (TLS Encrypted)	✅	✅	✅	✅
HTTP (Cleartext)	✅ (Default ON)	✅ (Default OFF )	✅ (Default OFF )	✅ (Default OFF )
HTTPS	❌	❌	❌	✅
Modbus TCP	✅	✅	✅	✅
Modbus TCP over TLS	❌	✅	❌	✅
Websocket	✅	✅	✅	✅
Websocket over TLS	❌	✅	❌	✅
UDP	✅	✅	✅	✅
UDP AES	❌	❌	✅	✅
mDNS Discovery	✅	✅	✅	✅

Important Note on TLS Resources: Due to the memory constraints of embedded devices, concurrent TLS connections (MQTTS, HTTPS, Websocket over TLS, Modbus over TLS) are strictly limited.

• For Basic+ firmware, a maximum of 1 TLS connection is recommended at a time.

• For Pro firmware, a maximum of 2 TLS connection is recommended at a time.

Please design your integration to reuse existing connections.

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4. API Reference Directory

Explore the sub-pages in this section based on your integration architecture:

🌐 Cloud & Backend Integration

• MQTT API Reference: The recommended protocol for continuous telemetry data streaming and cloud control. (Includes complete JSON payload definitions for voltage, current, power, etc. Note: The seq field is deprecated in Basic 5.1.14+).

🏠 Local Smart Home & LAN Integration

• mDNS Discovery: How to automatically discover Bituo meters on a local network without static IPs.

• HTTP API Reference: Standard RESTful endpoints (GET/POST) for local device configuration and on-demand data polling.

• WebSocket API Reference (Coming Soon): Real-time, bi-directional communication for local hubs like Home Assistant.

• UDP Broadcasting (Coming Soon): High-frequency, connectionless local data streaming for real-time energy monitoring and zero-export systems.

🔋 Local EMS & Gateway Integration

• Modbus TCP Map: Standard Modbus register maps for local energy gateways, solar/EV systems, and software-based building management systems (BMS).

📱 Mobile App & Proximity Control

• BLE Cleartext API: Bluetooth passthrough API for legacy Basic/Basic+ firmware.

• BLE Secured API: Encrypted PAKE Bluetooth API for Lite/Pro firmware, covering secure provisioning, local control, and encrypted energy data broadcasting.