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Smart Battery System Monitor

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  1. Smart Battery System Monitor ECE 445 Group 3 Jason Hoban David Atwood

  2. Introduction • This system installed in a car monitors the voltage and current from the lead-acid battery. • Prevents accidental battery depletion • Ensures car ignition capacity is maintained • Preserves the life of the battery

  3. Features • Real-time voltage and current monitoring to display battery voltage level and battery life remaining • Audio alert in car and to wireless receiver to warn of significant battery drain • Automatic cut-off of system loads to ensure ignition level charge remains • Simple one push reset to transfer control back to user

  4. Overall System

  5. Original Schematic – Car Side

  6. Original Schematic – RX Side and Load Switch

  7. MSP 430F156 • Reason for Selection • Low Power Consumption • High Functionality • 2x ADC, DAC, UART, Multiple Digital I/O • Size

  8. DC-DC Conversion • LM317 – 3 Terminal Adjustable Regulator • TX Side • 12 Volts to 3.3V and 5V • RX Side • 9 Volts to 5V DC-DC Schematic

  9. DC-DC Tests Transmitter Side Receiver Side

  10. Current Sense Module • LTC6101:High Voltage, High-Side Current Sense Amplifier • Precision .005Ω Sense Resistor Current Sense Schematic

  11. Current Sense Gain Tests

  12. Voltage Monitoring • Original Design • MAX6652 – Temperature Sensor and System Monitor • Revisions • Resistive Divider • Differential Amplifier Op-Amp Design Op-Amp Schematic

  13. Voltage Monitoring Tests

  14. Buzzer and Pushbutton • Piezoelectric Buzzer • Pushbutton De-bouncing Circuit Circuit and RC Equation

  15. Pushbutton

  16. De-bounced Pushbutton

  17. High Power Load Switch • High Ic rated NPN BJT • Smaller NPN BJT to drive the base • Controlled by MCU • Loads cut when Battery <= 11V Original BJT Switch Set-up

  18. BJT Design Constraints • HP BJT must be operated in saturatation • Initial tests show base current of at least 50mA required to drive base (VB=3.3V and IB = 50mA yields VCE = 210mV) • MSP430 I/O should not exceed 6mA • MPS2222 BJT rated at Ic,MAX = 600mA • Voltage from MSP430 must have enough headroom to operate all transistors at VBEON but not exceed current limit of the MPS2222

  19. Final Switch Set-Up • VOUT from MSP430 = 2.25V achieves IB,Q1 = 6mA • On-chip DAC required • Q1, Q2 drive 300mA into base of Q3 • Saturation achieved as evidenced by VCE,Q3 = 124mV and VLOAD = 11.79 V for a 11.95 V Battery Source Final Schematic

  20. TX/RX Circuit • LINX 416-ES Transmitter and Receiver • Design Changes • Frequency to Voltage Converter • Uses Transistor to Draw Required Current

  21. RX PCB • Created PCB • Issues with Incorrectly drawn trace and grounding • Scrapped to Proto Board

  22. TX Data Transmission

  23. LCD • PC-1602-Q 2x16 LCD with BPI-216 Serial Backpack • Serial RS-232 • Inversion Transistor required for UART output

  24. LCD Data Transmission

  25. Overall Power Determination

  26. Overall Power Consumption

  27. Successes • Interrupt Routine • Cutting off of loads • Pushbutton Reset • MSP Coding • Less readily available information than more common PIC Microcontroller option • LCD Display • Struggled with RS-232 and timing issues at first • Lack of Crystal at Deadline

  28. Challenges • I2C Code • Abandoned due to software issues and time constraints • ADC functionality allowed for Op-amp solution • TX/RX • Transmission Worked with Power Supply on Proto Board but full scale implementation created problems • PCB Issues

  29. Recommendations • With more time system could have been further optimized and expanded • MSP operation in Low Power Mode is made possible by sourcing clock from external 32kHz crystal • Further Research into using components with lowest power drain (i.e. instead of available LCD) • PCB Board Design could be greatly reduced in size • I2C Chip offered temperature monitoring • Time left Equation could be improved • Battery drain is not strictly linear • Averaging could produce more stable time left display

  30. Acknowledgements • Teaching Assistant Paul Rancuret • Professor Gary Swenson • Mark Smart and everyone else in Parts Shop • Professor Philip Krein • Texas Instruments for MSP Debugger Donation

  31. Questions ?