Project Goals

Our task was to take the proof of concept and make a production ready prototype with the following parameters

bull Use low cost microprocessorbull Add RS-232 IO functionalitybull Implement identical logic of original systembull Replace variable resistors with software timersbull Maintain all other specificationsbull Preserve existing product housing

bull Keith Benson ndash President Bonitron Incbull Stephen Collings ndash Engineer Bonitron Incbull Dr Andrew Dozier ndash EECS Professor Vanderbilt University

System Diagram PCB Design

Introduction

Sponsors

Bonitron HVAC Demand SchedulerAlexander Brown (EE) ndash Cory Haugh (EE) ndash Ajmer Dwivedi (ME)

Problem

Bonitron ceased producing the device when the microcontroller that it used went out of production Last year a design team successfully documented all the components used in the original demand scheduler They also generated system diagrams circuit schematics and logic diagrams corresponding to the original design This year our goal was to engineer a production ready prototype and deliver it to Bonitron

The Bonitron HVAC Demand Scheduler is a device that reduces the peak power consumption in a building running two HVAC units It interfaces with the thermostats and only allows one unit to run at a time (unless a user overrides this functionality) By lowering peak power consumption the demand scheduler can drastically lower utility bills

Proof of Concept Designed Last Year

Main Board

Power Conversion

Signal Conversion

120V AC Power Supply

Thermostat 1

Thermostat 2

Heat

AC

Controller

Output Relays

Heat

AC

HVAC 1

HVAC 2

RS232 Conversion

Computer

5V

ONOFF

ONOFF

Demand 1

Demand 1

Gnd

PicKit 2 Programmer

Vpp

PG

D

PG

C

ProgrammingHeader

Vp

p

PG

D

PG

C

RxD

TxD

Vcc Heat

RxD

TxD

RxD

TxD

Gnd

Vpp PGD PGC

RA0RA1RA2RA3RA4

RA0RA1RA2RA3RA4

RD0

RD1

Ribbon Cable

Display Board

LEDs (5)

Control Buttons (2)

D0D1D2D3D4

RD2RD3

D0D1

ACSignal Gnd

ONOFF

ONOFF

RB0

RB1

RD2RD3

Signal Gnd

Signal Gnd

ONOFF

ONOFF

Signal Gnd

Signal Gnd

Signal Gnd

Heat

ACSignal Gnd

Signal Gnd

Signal Gnd

VccGnd

VccGnd

120V AC

System GndAC Neutral

Chassis Gnd

bull Four main functions Power conversion signal conversion RS-232 communications and microcontroller

bull Demands from the thermostats are routed to the microcontroller The microcontrollers decision to activate a unit is based on parameters set by the user

Microcontroller SelectionName Cyclone II FPGA HCS12 87C51 PIC16F747

Part Number EP2C35F672C8N MC9S12UF32 P87C51FB-4N PIC16F747

Producer Altera Freescale NXP Microchip

Unit Cost $9970 $420 $780 $320

Package 672-FBGA 64-LQFP 40-PDIP 40-PDIP

Programming Software Quartus II MGTEK MiniIDE Third Party Bundled with PicKit

Cost 000 000 000 000

Programming Hardware Serial Port Cable USB Cable ZIF Socket + USB PicKit 2

Cost $15000 $10000 $11000 $5000

Programming Language VHDL Assembly C Assembly Assembly C

Custom Header Y Y N Y

Timers N Y Y Y

RS-232 N Y Y Y

Internal Clock N N Y Y

Non-Volatile Code N Y Y Y

Notes

Previous grouprsquos FPGA used in FPGA

class at Vanderbilt

Used in microcontroller class

at Vanderbilt

Microcontroller currently used in Bonitron Board Lowest Cost to Project

Development Approach

bull Use PICkit 2 development environment

Hardware programmer for PIC microcontrollers

USB programmable

Connects via 6 pin header on PCB

Packaged with starter kit for testing

bull Copied 90 from previous PCB layout

bull Added connections for new microcontroller and serial communications

bull 2 sided through hole design allows easier trace routing than previous single sided board

PCB floorplan PCB trace layout

Graphical User Interface

bull GUI controls timers and overrides

Parallels functionality of previous override design

Replaces variable resistors with programmable timing capabilities

bull Allows user to program timers without physically manipulating components

bullTested using feedback loop

GUI Testing Using Feedback Loop

Assembly and Testing

bull PCB fully assembled and functional

bull GUI functional and communicating with PIC16F747 microcontroller