> For the complete documentation index, see [llms.txt](https://docs.bituo-technik.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.bituo-technik.com/device-api/spm-sdm-open-wi-fi-api-overview.md). # SPM/SDM Open Wi-Fi API Overview ## Open Wi-Fi API Overview {% hint style="info" %} **Status:** Active | **Applies to:** SPM/SDM Open Wi-Fi Series (ESP32-8685 / C6) | **Updated:** 2026-07-12 {% endhint %} ### 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. *** ### 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). *** ### 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)** |

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| | **HTTPS** | ❌ | ❌ | ❌ | ✅ | | **Modbus TCP** | ✅ | ✅ | ✅ | ✅ | | **Modbus TCP over TLS** | ❌ | ✅ | ❌ | ✅ | | **Websocket** | ✅ | ✅ | ✅ | ✅ | | **Websocket over TLS** | ❌ | ✅ | ❌ | ✅ | | **UDP** | ✅ | ✅ | ✅ | ✅ | | **UDP AES** | ❌ | ❌ | ✅ | ✅ | | **mDNS Discovery** | ✅ | ✅ | ✅ | ✅ | {% hint style="warning" %} **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. {% endhint %} *** ### 4. API Reference Directory Explore the sub-pages in this section based on your integration architecture: #### 🌐 Cloud & Backend Integration * [**MQTT API Reference**](/device-api/spm-sdm-open-wi-fi-api-overview/mqtt-api-reference.md): 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**](/device-api/spm-sdm-open-wi-fi-api-overview/mdns-discovery.md): 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.