A homemade voltage monitor for car’s battery as well as its charging system is presented by this project which can be applied to modern automobiles.
The faulty charging system is one of the most common reasons for a car battery failure where the battery does not get the proper charging voltage if the charging system is not working properly. The system is designed to display the instantaneous output voltage across the battery terminals on a 4-digit 7-segment LED display by plugging into the cigarette lighter receptacle of the car. For possible charging system and battery problems, it will provide early warnings. To achieve a very precise and accurate A/D conversion of the battery voltage, the main controller used by the project is the PIC16F1827 which uses the built-in Fixed Voltage Reference (FVR) module.
During the operation, the actual output voltage from the battery is the voltage measured by the device when the engine is turned OFF. The charging voltage across the battery that is coming from the car’s charging system is measured when the engine is turned ON or the car is running. Using a regulator IC, the car’s output voltage provides the 5V supply for the PIC16F1827 microcontroller circuit.
To measure the voltage across the terminals, the PIC16F1827 uses the AN4 ADC channel. To prevent the voltage at the MCU’s ADC channel from going above 5.1V, the 5.1V Zener diode is placed in parallel with R2 which increases or decreases the range of input voltage.