Digital Automatic Climate Control by ewghwehws


            Insert picture of old
Automatic   amplifier board and
            new blowerboard

              Senior Design II
              Mississippi State
Team Members

 • John Dillingham
    MATLAB Simulation
 • Tony McDowell
    Testing and Test Environment
 • John Robbins
    System Control Firmware
    Schematic/Layout
 • Brett Wisinger
    Testing
    Documentation
                   Existing system Expensive
 Problem:                and Unreliable

• Many common failures
• Repair costs $525-$1200
• Repair still contains flawed design
Solution: Drop-in Replacement

                              Block Diagram
                                                                     Vehicle Power Input
                                            DACC Project

 Type II ACC
                                                   DACC System
     Sensing Chain
          In-car          Ambient
          Temp             Temp
                                                                       Processor Module

         Defrost       High Blower

               User Interface                              Coolant      Vacuum             Blower
                                                           Module       Module             Module
               Desired Temp
Solution: Drop-in Replacement

• Duplicates or improves existing
• PWM control of blower speed
• Reliable and off-the-shelf coolant valve
• Industry standard vacuum valves
• Reduced cost with increased reliability
    Last Semester’s Progress

• Functioning Prototype
• Initial Test Environment
• Revision A of PCB
• First Generation of Software
• Analyzed Existing Temperature Sensor
  Chain Input
• Cost of PCB and components $50-80
    Goals for this semester

• Packaging
• Fine-Tune Software (PID)
• Reduce Transients on Blower Motor
  Controller MOSFET
• Increase Heat Transfer Capability
• Revise PCB to Correct Errors
• Improve Test/Demo Environment
     Required PCB Revisions

• Wrong MAX232 Footprint
• I2C Problems
• Add Inputs for Blower High and Defrost
• Improve Programming header
• Increase size of PCB heatsink for stepper motor
• Interface with vehicle connectors
• Improve off board connections (stepper motor, etc)
         Progress: General

• Solenoid Vacuum Switches finalized, received,
  and initial testing complete.
• Temperature chamber model added to system
• Split single PCB into Main System Board and
  Blower Board
• Blower Board PCB manufactured, awaiting
• Main System Board 80% complete
• Component BOM 95% complete
 Progress: MainSystemBoard

• Main System Board:
  • New μC: PIC18F45J10
      • Master I2C Support
      • 61% cost reduction (~$9.65 to ~$4.05)
  •   Standard ICSP program header
  •   Stepper motor controller PCB heatsink increased
  •   Car connectors plug directly to PCB
  •   Capability for communication through either
      RS232, USB, or Bluetooth. User selectable
Blower Transients: Before
Blower Transients: After
Blower Transients: Before
Blower Transients: After
     Progress: BlowerBoard

• Blower Board
  • Previous Design
    • Dissipates ~16-20W (MOSFET On RDS = 40mΩ)
    • Needs large heatsink to meet design constraints
    • Physically located on MSB in engine compartment
  • New Design
    • Dissipates less than 1W (MOSFET On RDS = 2mΩ)
    • Uses PCB as heatsink
    • Physically located in the glove box
 Special Concerns: Economic

• Existing replacements cost anywhere from
  $525 for a rebuilt unit to $1400 for a new
  OEM unit
• Cars the system is applicable to are up to
  30 years old
• Repair to vehicle cost ratio is excessively
 Special Concerns: Economic

Item                           Cost
PCB Components                 $70
Main System Board PCB          $13
Blower Board PCB               $13
Vacuum Valves                  $125
Coolant Valve Assembly         ~$100
Misc. Packaging and Hardware   $30

Total System Cost              $351
 Special Concerns: Economic

• Current system cost of $350 allows for a
  slim margin for manufacturing and profit
• Packaging materials and coolant control
  assembly are main opportunities for cost
Special Concerns: Environmental

• Harsh environment underneath hood
  • Components located in engine compartment must
    operate at 170°F
  • Components must be packaged to avoid contact with
    destructive elements (salt spray, humidity, etc)
• Coolant can reach 212°F
  • Valve must operate at 250°F
• Glove box environment is mostly plastic
  • Components in glove box environment must not
    exceed 140°F
    Test Plan - Vacuum Control

• Module test to         • Status
  power LEDs               • LEDs power on as
• Module test to drive       expected
  up to 1, 2, and 3        • Solenoid’s indicator
  vacuum solenoids           and audible click
  simultaneously             indicate actuation
• Module test to use       • Need fittings to
  vacuum valves to           connect to vehicle
  direct vacuum to           and perform flow test
    Test Plan - Blower Control

• PWM Output Tests        • PWM Status
  • Logic level present     • Rev A PCB
  • LED brightness            successfully
    control                   passed all tests
  • Small current load      • Rev B PCB is in,
    control                   awaiting parts
  • Vehicle blower
    motor control
   Test Plan – Blower Control

• Constraint Tests      • Constraint Status
  • 11-14.4V input        • Rev A passed voltage and
    voltage range           current tests. Awaiting
  • 16A Current limit       components for further
  • 140°F temp limit        results
                          • Rev A temperature higher
                            than limit by 40°F
                          • Rev B significantly reduces
                            power dissipation. Awaiting
                            components for test.
         Test Plan: Unit Tests

Vacuum Control Module
• Module tests to power LED’s (corresponding to
• Module tests to drive combinations of1, 2, and 3 different
  vacuum solenoids
        Test Plan: Unit Tests

Blower Control Module
•   Module tests for 11.0-14.4V input voltage range
•   Module test for proper PWM signal generation
•   16A Current limit
•   140°F temp limit
         Test Plan: Unit Tests

Vacuum Control Module
• Module tests to power LED’s (corresponding to
• Module tests to drive combinations of1, 2, and 3 different
  vacuum solenoids
   Test Plan: Functional Tests

System Response
• Test system for delayed response to user input (>= 5.0
• Test system for proper response to user input
• Test environmental tolerances
   • Test that blower control module does not exceed 140F
   • Test that main system operates at an ambient temperature of
   • Test that coolant control module withstands temperatures of
   Test Plan: Functional Tests

System State
• Test system for proper state transitions
• Test system for proper current state given current
   • Proper air flow routing
   • Proper vacuum solenoid routing
   • Proper stepper motor position
   • Proper blower motor speed

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