Digital Automatic Climate Control Senior Design II Mississippi State University Insert picture of old amplifier board and new blowerboard

Team Members John Dillingham  MATLAB Simulation Tony McDowell  Testing and Test Environment John Robbins  System Control Firmware  Schematic/Layout Brett Wisinger  Testing  Documentation

Problem: Many common failures Repair costs $525-$1200 Repair still contains flawed design Existing system Expensive and Unreliable

Solution: Drop-in Replacement

Duplicates or improves existing functionality 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 controller 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 simulation Split single PCB into Main System Board and Blower Board Blower Board PCB manufactured, awaiting components 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 option

Blower Transients: Before

Blower Transients: After

Blower Transients: Before

Blower Transients: After

Progress: BlowerBoard Blower Board Previous Design Dissipates ~16-20W (MOSFET On R DS = 40mΩ) Needs large heatsink to meet design constraints Physically located on MSB in engine compartment New Design Dissipates less than 1W (MOSFET On R DS = 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 high

Special Concerns: Economic ItemCost 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 reduction

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

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

Test Plan – Blower Control Constraint Tests V input voltage range 16A Current limit 140°F temp limit Constraint Status Rev A passed voltage and current tests. Awaiting components for further 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 solenoids) Module tests to drive combinations of1, 2, and 3 different vacuum solenoids

Test Plan: Unit Tests Blower Control Module Module tests for V 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 solenoids) 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 seconds) 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 170  F Test that coolant control module withstands temperatures of 215  F

Test Plan: Functional Tests System State Test system for proper state transitions Test system for proper current state given current conditions Proper air flow routing Proper vacuum solenoid routing Proper stepper motor position Proper blower motor speed

Questions