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This system installed in a car monitors the voltage and current from the lead ... Audio alert in car and to wireless receiver to warn of significant battery drain ...

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Smart battery system monitor l.jpg

Smart Battery System Monitor

ECE 445 Group 3

Jason Hoban

David Atwood


Introduction l.jpg
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


Features l.jpg
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





Msp 430f156 l.jpg
MSP 430F156

  • Reason for Selection

    • Low Power Consumption

    • High Functionality

      • 2x ADC, DAC, UART, Multiple Digital I/O

    • Size


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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


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DC-DC Tests

Transmitter Side

Receiver Side


Current sense module l.jpg
Current Sense Module

  • LTC6101:High Voltage, High-Side Current Sense Amplifier

  • Precision .005Ω Sense Resistor

Current Sense Schematic



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Voltage Monitoring

  • Original Design

    • MAX6652 – Temperature Sensor and System Monitor

  • Revisions

    • Resistive Divider

    • Differential Amplifier Op-Amp Design

Op-Amp Schematic



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Buzzer and Pushbutton

  • Piezoelectric Buzzer

  • Pushbutton De-bouncing Circuit

Circuit and RC Equation




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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


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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


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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


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TX/RX Circuit

  • LINX 416-ES Transmitter and Receiver

  • Design Changes

    • Frequency to Voltage Converter

    • Uses Transistor to Draw Required Current


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RX PCB

  • Created PCB

    • Issues with Incorrectly drawn trace and grounding

    • Scrapped to Proto Board



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LCD

  • PC-1602-Q 2x16 LCD with BPI-216 Serial Backpack

  • Serial RS-232

    • Inversion Transistor required for UART output





Successes l.jpg
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


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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


Recommendations l.jpg
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


Acknowledgements l.jpg
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



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