Wireless chat between a HM-TR module and the AVR microcontroller


Wireless chat with the HM-TR-TTL modules and the Atmel AVR Microcontrollers

This project has done based on the Atmel AVR microcontrollers and the HM-TR Radio Modules. In this project two the same circuits are connected to two PC computers. The maximum distance between these computers is 300 meters and they can share data between together.

Two programming languages are used in this project. Firstly the C language is used to program  Atmel AVR microcontrollers and another is Delphi to generate a program to make a connection between two computers by their HM-TR module software wise.

Figure 1

The HM-TR -232 Module

Figure displays a HM-TR module

Description of HM-TR module

HM-TR series transparent wireless data link module is developed by Hope microelectronics Co. Ltd, dedicated for applications that needs wireless data transmission. It features high data rate, longer transmission distance. The communication protocol is self controlled and completely transparent to user interface. The module can be embedded to your current design so that wireless communication can be set up easily.


  • FSK technology, half duplex mode, robust to interference
  • ISB band, no need to apply frequency usage license
  • Operation frequency can be configured and can be used in FDMA applications
  • Transmitted frequency deviation and receiver bandwidth can be Selected.
  • Protocol translation is self controlled, easy to use.
  • Data rate can be Select From a wide range.
  • Provide ENABLE pin to control duty-cycle to satisfy different application requirements
  • High sensitivity, long transmission range.
  • Standard UART interface, TTL or RS232 logic level Selectable
  • Very reliable, small size, easier mounting.
  • No tuning in producing


  • Remote control, remote measurement system
  • Wireless metering
  • Access control
  • Identity discrimination 5. Data collection
  • IT home appliance
  • Smart house products
  • Baby monitoring

How the system works?

When the HM-TR module’s terminal is connected to a power supply source, it should send and receive data simultaneously, firstly it sends the data with its DRX pin and then automatically switches to a receiving data mode. If there is data in a receiving mode, it receives it with its DTX pin. The needed time to switching between these two modes is 50 ms.

Two types of this modules are available. The HM-TR-TTL functions based on TTL logic level and HM-TR-232 functions based on RS232 logic level. It has a Max232 IC on the board, so it can connect directly to a serial port of a computer.

You may download the full description of this project in a PDF format which gives you more detailed information about this project and its developed related code (the code developed for the Atmel AVR microcontroller  using codevision avr software and handshaking code used to establish communication between the microcontroller and the PC using , Delphi program , … ), and finally the PCB schematic using Protel  Altium(R) software by clicking HERE

Figure 3  displays a HM-TR Module and its related antenna

Figure 4 displays the HM-TR-232 pin designations

Figure 5 displays the schematic diagram of the PCB developed to build two PCBs that each  is housing an Atmel AVR microcontroller,  a LCD display (not installed in this project) and a RS232 IC to make the communication possible between each PCB and the PC.

Figure 5 displays a typical USB 2.0 to Serial (9-Pin) DB-9 RS-232 Converter Cable that provides the connection between USB and the traditional RS-232 serial port

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