This is the HC-21 an embedded Wi-Fi UART module built IEEE802.11 wireless network protocol stacks and TCP/IP protocol to achieve conversation between serial data to wireless network communication. The HC21 can be connected via wireless to wireless without any support of microcontroller works as standalone, or master/client mode. For example if you want to extend your RS485 communication to wireless 2.4GHz to extend the monitoring capabilities.

HC-21 module also support STA access as Infra network or Ad-hoc, soft AP, for handheld terminal access function and support TCP/UDP/ARP/ICMP/HTTP/IGMP/PPPOE/DHCP / DNS to provide smart terminal devices. HC 21 runs on 3.3v at 560mW Typical, support baud rate range to 1200 ~ 460800bps, up to 4 station can be setup, adapt OPEN/WEP/WPA-PSK/WPA2-PSK authentication, provides server software, application software, mobile Application design customization, support open source industrial protocols like (MODBUS) etc. can be configured using AT+ CMD instruction set on multiple parameter or configure via web interface. This device can be implemented in Industrial / Automotive electronics control, smart grids, IOT, Intelligent appliance and smart home.  For more details please refer to the datasheet below.

Required Components

  • Arduino Microcontroller, Teensy (Teensy Duino), ATMEGA328 16/12, ATMEGA32u4 16/8/ MHz, ESP8266, ATMEGA250 16 MHz, ATSAM3x8E, ATSAM21D, ATTINY85 16/8 MHz (Note: The Diagram below is using NANO. If you’re using other MCUs please refer to the respective pin-outs diagram)
  • HC-21 EMBED 2.4GHz Serial UART Module
  • FTDI USB Serial Interface (Optional)
  • Jumper Wire / DuPont Wire
  • Bread Board / Solder Less Bread Board

Pin-Out Diagram

Wiring Guide

Network Implementation Diagram

Sketch Code


  • Download HC-21 Documentation | Zip
  • Download HC-21 Documentation Datasheet | Zip
  • Download HC-21 Easy Simple WiFi Tool | Zip
Wiring HC-21 (M02) 2.4GHz Wi-Fi Serial Universal Asynchronous RX/TX on Microcontroller
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