HLK-RM04 Embedded UART-ETH-WiFi Serial Module

The HLK-RM04 is a low-cost embedded module developed by Shenzhen Hi-Link Electronic that enables bidirectional conversion between a serial UART interface, Ethernet, and a 2.4 GHz WiFi network. Built around the Ralink RT5350 SoC, the module integrates a 360 MHz MIPS CPU, 16 MB of SDRAM, and 4 MB of flash memory, providing a complete networking solution without requiring the user to modify the existing serial device. A built-in TCP/IP protocol stack handles network communication, while an internal web server allows parameter configuration through a standard browser. The module also supports the AT command set for straightforward serial-based setup and control.

The HLK-RM04 WiFi module supports IEEE 802.11 b/g/n wireless standards with data rates of up to 150 Mbps in 802.11n mode, alongside wired connectivity through 10/100 Mbps Ethernet interfaces. It can operate in Client, AP, and Router modes, and includes WDS bridging, WEP/WPA/WPA2 security, and DHCP/DNS functionality. The board is equipped with an onboard antenna and also provides a connector for an optional external antenna, giving flexibility in signal coverage. Measuring just 80 × 50 × 18 mm, it fits easily into compact enclosures. The module is widely used to add WiFi and Ethernet connectivity to legacy serial equipment, IoT devices, industrial controllers, and portable electronics, allowing traditional UART-based products to transmit data over IP networks with minimal integration effort.