Bonitron Air Demand Scheduler Design Review Vanderbilt Senior Design Alex Brown Ajmer Dwivedi Cory Haugh February 04, 2008

Introduction Air Demand Scheduler Reduces peak power consumption Selects 1 of 2 HVAC units to run at a time Allows for manual control using user overrides

Objectives Production ready prototype Low cost microprocessor RS-232 I/O functionality Identical logic All other specifications are to remain the same Preserve existing package

Requirements Input Power Control Signals 24 VAC Enclosure 115VAC, 50/60Hz Control Signals 24 VAC Inputs Thermostat 1: Air Conditioning 1, Heat 1 Thermostat 2: Air Conditioning 2, Heat 2 Outputs Unit 1: Air Conditioning 1, Heat 1 Unit 2: Air Conditioning 2, Heat 2 Enclosure NEMA-12 Wall Mountable w/Quick Release Door Latch (10’’ x 6’’ x 4’’) Operating Temperature 0 to +40 Degrees Celsius Storage Temperature +20 to +65 Degrees Celsius Humidity Below 90% Atmosphere Free of Corrosive Gas and Dust

Approach Extract existing design from previous group’s documentation and new hardware Replace FPGA development kit with microcontroller Develop PCB design partitioning circuit components Fabricate assemble and test design

System Diagram

Power Conversion Diagram

Power Conversion Schematic

Power Conversion Requirements Provides conditioned power to Signal Conversion Board Inputs 115 VAC IN Outputs +18 VDC (nominal) OUT +5 VDC OUT

Signal Conversion Diagram

Signal Conversion Schematic

Signal Conversion Functional Requirements Inputs Thermostats provide 24 VAC upon Demand 2 Heat Inputs 2 Cool Inputs Outputs Replaces thermostats to HVAC units 24 VAC sent to HVAC units via relays based on decisions made by microcontroller, I/O Board, or user interface Optical Isolation Optocouplers isolate and protect microcontroller & I/O Board from outside 24 VAC circuitry

Signal Conversion 24 VAC Input from Thermostats Conditioned and rectified Electrically Isolated Sent to microcontroller & I/O Board If +5 VDC from microcontroller Amplified via Darlington array to turn off relay If 0 VDC from microcontroller Grounds output of Darlington array to turn on relay 24 VAC Output to HVAC Sent via closed relay

Microcontroller Selection Name Cyclone II FPGA HCS12 87C51 PIC16F747 Part Number EP2C35F672C8N MC9S12UF32 P87C51FB-4N Producer Altera Freescale NXP Microchip Recurring Cost $99.70 $4.20 $7.80 $3.20 Package 672-FBGA 64-LQFP 40-PDIP Programing Software Quartus II MGTEK MiniIDE Third Party Bundled with PicKit Programing Hardware Serial Port Cable USB Cable ZIF Socket + USB PicKit 2 Programing Cost $150.00 $100.00 $110.00 $50.00 Programing Language VHDL Assembly \ C Assembly Custom Header Y N Timers RS-232 Internal Clock Non-Volatile Code Notes: Previous groups FPGA, used in FPGA class at Vanderbilt Used in microcontrollers class at Vanderbilt Microcontroller currently used in Bonitron Board Lowest Cost to Project

Microcontroller Selection Cyclone II FPGA High recurring and non recurring costs Surface mount with 600+ pins HCS12 Surface mount High non recurring costs 87C51 Third party programming software No C++ support

Microcontroller

Development Approach Programmable microcontroller Internal UART Internal timer Internal oscillator Compatible with original microcontroller (40 pin DIP) Use PICkit 2 programmer and development kit to code microcontroller

Development Methodology User will write the application program in C or assembly code On-board storage RAM Configuration retained as long as the power is on Flash Store program code in non volatile memory

MPLAB IDE Development Software Software provided by Microchip for programming PIC microcontrollers Procedure: Write code in assembly language Program microcontroller Test functionality Apply test inputs and observe outputs Design test strategy for all possible cases

MPLAB IDE Screenshot

PICkit 2 Hardware programer for PIC microcontrollers USB programmable Connects via 6 pin header on PCB Packaged with starter kit for testing

Existing Logic Diagram

RS-232 Graphical user interface for control of overrides and timers Parallels functionality of previous override design Replaces variable resistors with programmable timing capabilities Allows user to program timers without physically manipulating the components

Programming RS-232 GUI done using Visual Basic Use feedback loop to perform original testing

RS-232 Hardware Max 232 transceiver to perform voltage conversion between circuitry and DB-9 Changes voltage range from 0 - 5 VDC to ±15 VDC

Floorplan

PCB Design Copied 90% from previous PCB layout Added connections for new microcontroller and serial port components 2-sided through hole design allows easier trace routing than previous single sided board

PCB Software Developed PCB design using PCBExpress No License required Order directly though the site Extensive parts library Ability to design custom component based on datasheet specification

Bottom Side

Top Side

PCB Design

Approval In order to proceed, we request your approval of the design Comments?

Near Term Plan Hardware Development Add breakpoints to existing PCB design Obtain parts from Bonitron storeroom (Maybe) Order parts for test boards (don’t tell Bonitron) Order PCB Test circuit partitions Assemble Test Final product

Near Term Plan Software Development Develop assembly language code Refine Visual Basic GUI

Hardware Schedule Obtain all components by February 15th Order PCB by February 15th Have assembled prototype boards by March 1st Have full board assembled by March 14th Test till design day (and pray)

Software Schedule Complete GUI by February 22nd Complete programming of the test board microcontroller by March 1st Complete programming of product ready prototype board microcontroller by March 14th System debug and operational testing from March 14 until design day

Our webpage: http://eecs.vanderbilt.edu/courses/eece295/2007-2008/Bonitron-HVAC