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A BETTER BATTERY CHARGER

Part 2: Hardware and Software Implementation
by Thomas Richter

Start ý The Buck Converter ý Voltage Reference and Battery Temperature ý AT90S2333 Battery Charger ý ATtiny15 Battery Charger ý Charge Current ý Software Implementation ý User Settings ý Source Code ý INT Battery Function ý The Stable_ADC Function ý BC.H ý B_DEF.H ý Charge MethodýSLA.C ý Charge MethodýNiCd.C and NiMH.C ý Charge MethodýLilon.C ý Suggested Improvement ý Sources and PDF

SOURCE CODE

In this section, Iýd like to talk about some of the source code files for the battery charger reference design (see Tables 2 and 3). Also note that Iýve made the C source code and the assembly source code available for downloading.

First, letýs take a look at BC.C. This module contains the main function, the setup and UART functions, real-time clock, and interrupt handling routines.

During the setup routine, all low-level initialization is done. The UART is initialized and the real-time clock is set to zero. After initialization, the program loops in idle mode until the status is changed in the global status variable.

The real-time clock is started and stopped when the PWM is started and stopped (i.e., when the battery voltage is measured). This ensures that the only time taken into account is when the battery is charged. On the other hand, the disadvantage is that measurements, which rely on time (dV/dt or dT/dt), may be inaccurate.

You can cause an external interrupt by pressing a button to change the charge status. During the interrupt handling routine, the status is changed according to the button pressed, either to fast-charge or trickle-charge. During the main function, the program then calls a function depending on the value set in the "charge status" variable (see Figure 5).

BC.C also includes some common functions used by the different battery programs. The two most important are the int battery (unsigned char value) and the void stable_ADC (void).

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