I2C communication module
Oz89 sampling module sends the collected and processed data to LF2407 through I2C bus. Since LF2407 does not have I2C interface, this design uses pca9564 to expand its I2C interface. In order to prevent electromagnetic interference from affecting the data transmission on I2C bus, the bus signal must be isolated. Considering that I2C bus is bidirectional transmission, adum1250 bidirectional isolation chip is used for isolation. Pca9564 and bidirectional isolation circuit are shown in Figure 2.
Figure 2: pca9564 and bidirectional isolation circuit
Serial communication module
The battery management system sends the collected and processed data to the PC interface through the serial port to realize human-computer interaction. Through the serial interface, you can observe the parameters such as the total voltage, monomer voltage, current, SOC, fault state, charge and discharge power of the battery, and can also send through the serial port to realize the online calibration of the management system. Its hardware circuit is mainly based on MAX232 chip, as shown in the figure).
Figure 3: serial communication interface circuit
MAX232 is a transceiver with + 5V power supply, which is connected with the computer serial port to realize the level conversion of RS-232 interface signal and TTL signal, so that BMS and PC can carry out asynchronous serial communication. In order to prevent electromagnetic interference from affecting the data transmission on the serial port, the bus signal must be isolated. The serial port is unidirectional transmission, so it is more convenient to use 6n137 photoelectric coupling) as the 232txd signal optocoupler isolation circuit.