Building a car battery data logger Part 1 Introduction and its hardware design
Overview of Car Battery Data Logger
I thoroughly enjoyed my internship at RS – the world’s leading high-service distributor of electronics. As a student intern, I had learned a lot of skills and knowledge about monitoring systems and web applications including MySQL.
The aim of this project was to monitor the voltage of the car battery and the current passing through it. Afterwards, the information was sent to a web server through a Wi-Fi module and then to create those records in the database. Finally, the battery information was displayed on a web page in the form of a line graph with double Y-axis and an X-axis for displaying voltage, current and time respectively.
Image 1: Example of plotting line graph by use of data set in the database
For evaluating battery health and performance, time information was loaded to every voltage-current data set.
The main idea of this project was to improve the emergency services of an ambulance. By monitoring and analyzing the battery to ensure robust emergency services to the public and save the life of people who are in need.
Operation principle of data logger
In this project, STM32F407VGT6 was adopted for ADC. The maximum allowed voltage feed into PC1 is Vref , 3.3V. However, a 12V car battery was the target being monitored. So, a differential amplifier was included to suppress the voltage so as to perform ADC. A low pass filter was used as a load to reduce the noise.
Image 2: Voltage monitoring part
On the other hand, the current passing through the current transducer was then transformed into a voltage value in the range of -15V to +15V. In view of this, A step up process must be included in the design. Therefore, IC3a was included to make sure that I_SEN_IN voltage value was not negative.
Image 3: current monitoring part
For time information, DS1302 was adopted in this project. The advantage of using DS1302 is to provide more accurate time information and to make sure that even in case of MCU is disconnected from a power source, the clock will continue to perform counting.
Image 4: DS1302 design
For details of hardware design, you can refer to the attachment about schematic diagram as below.
Image 5: Schematic diagram of car battery data logger project
Finally, the product looks like below.
Image 6: Final product of car battery data logger
In the next part, I will talk about how to program an MCU to perform ADC.