I designed the PCBs under Altium Designer Winter 09 , an EDA software suite newer than DXP 2004. The main structure and functions of controller and Extended board are identical to those of the previous version while some hardware modifications are conducted, and the major changes are described as follow.

• The programming port changes from parallel to universal serial bus (USB);
• I replace the original 38 kHz generator with a new one;
• Four keys for selecting subroutines are introduced to the controller
• A MAX232 transistor-transistor logic (TTL) to RS232 level translator newly works on the extended board for communicating with devices obeying RS232 protocol;
• The radiator fan is abandoned;
• The new design of extended board allows mounting a LCD module;
• I redraw the schematics into layers;
• The electrical wirings on both main controller and extended board are reconstructed.

The hardware driver programs are totally rewritten for version 2.5. I abandon AVR-GCC and adopt AVR-G++ , the GNU C++ compiler for AVR, to develop the hardware driver. Thanks to the object-oriented programming (OOP) features, I encapsulated the drivers for all hardware modules into classes and offer users interfaces to initialize and to control the modules; thus, the code becomes much more user friendly, secure, and flexible than before; furthermore, the maintenance and update to the driver programs are easier for me. The driver for each module is also more sophisticated: it can use different functions of a module when being passed specific parameters. For example, users can determine whether to initialize a T/C to pulse-width modulation mode, timer mode, or any other mode.

However, AVR-G++ still has some restrictions such as not supporting “new” and “delete” operators; thus, I cannot create objects dynamically. Although the standard C Language function malloc() can allocate memory dynamically while function free() can release the memory, they do not support OOP: they never call the constructor and destructor of an object; therefore, AVR-G++ still does not meet my require perfectly.

During the development of driver version 2, I use a different IDE from that used in the previous version because the new IDE – Eclipse – is more powerful in source code management and in providing code context, which enhances my coding efficiency considerably.

The driver program for version 1.0 instructs users to write foreground- background processing client code; nonetheless, the driver for version 2.5 equips a preemptive RTOS called FreeRTOS , which also supports time slicing tasks; thus, the user code is not an endless loop, instead, should be written in several subroutines. I embed AVRX into my own programs to make it more powerful: users can select different tasks to run each time when the system starts.