Proposal
Adaptive Thermostat Using Bluetooth
ECE4007 Senior Design Project
Section L02, Group7
Scott Snyder, Team Leader
Thomas Lawrence
Jennifer Ogunlowo
Mark Youngblood
Submitted
September 17, 2007
TABLE OF CONTENTS
Executive Summary ......................................................................................................... iii
1. Introduction ..................................................................................................................1
1.1
1.2
1.3
Objective .............................................................................................................1
Motivation ...........................................................................................................2
Background .........................................................................................................2
2. Project Description and Goals ....................................................................................3
3. Technical Specification ................................................................................................5
4. Design Approach and Details ......................................................................................6
4.1 Design Approach ..................................................................................................6
4.2 Codes and Standards .............................................................................................7
4.3 Constraints, Alternatives, and Tradeoffs ..............................................................8
5. Schedule, Tasks, and Milestones.................................................................................9
6. Project Demonstration...............................................................................................11
7. Marketing and Cost Analysis ....................................................................................11
7.1 Marketing Analysis .............................................................................................11
7.2 Cost Analysis ......................................................................................................12
8. Summary .....................................................................................................................16
9. References ...................................................................................................................17
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EXECUTIVE SUMMARY
The adaptive digital thermostat is a cost-effective and facile system that allows inhabitants of
commercial and residential premises to maintain a preferred temperature without any physical
adjustment. A Bluetooth-enabled thermostat can detect the presence of an individual carrying a
cell phone with a Bluetooth adapter in a home, apartment, or office. The thermostat then adjusts
the temperature setting for the house according to which cell phone is present. The current status
of the system is displayed on an LCD display. This display includes the desired and current
temperatures.
The result of this project will be a fully functional prototype. The prototype will not be ready-tomarket since it will not be in the proper form-factor. It will be able to detect a nearby unique
Bluetooth-enabled cell phone, retrieve the corresponding preferences from memory, change the
desired temperature, and turn on the air conditioner or heat pump until the desired temperature is
reached.
A thermostat that senses the presence of people and manipulates the temperature of an area
accordingly has yet to be produced commercially. Entering this untapped market will cost
$124.50 per unit for parts and labor. To achieve the desired 10% profit margin the units should
be sold at a price of $136.95. At this price point, the adaptive thermostat will be affordable for
consumers as it is slightly less expensive than a high end thermostat found in many homes.
There is also potential to market a home automation package that would include the adaptive
thermostat along with other products, such as automated lighting.
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Adaptive Thermostat Using Bluetooth
Adjusting the temperature of a room based on who is present has yet to be done because the
Bluetooth technology that makes it affordable has only recently come to maturity.
1.
INTRODUCTION
Project engineers will design and prototype an adaptive thermostat that can manipulate the
environment temperature based on how many people are in the room and who those people are.
The thermostat will be equipped with a Bluetooth adapter that will detect the presence of a
person’s Bluetooth-enabled cell phone. After the person is detected, a microcontroller will lookup that person’s preferences and send the proper signals to the thermostat to correct the
temperature.
1.1
Objective
The purpose of the adaptive thermostat is to bring personalized automated comfort to a home.
An adaptive thermostat could be installed in a home as an independent system, or it could be one
part of a system that enhances a home by making it more responsive and automated. In both
cases, it will be used by people who already have a Heating, Ventilation, and Air Conditioning
(HVAC) system and a Bluetooth-enabled cell phone.
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1.2
Motivation
A system that automatically reacts to the people in the room has yet to be developed. Along with
increased comfort, utilizing the adaptive thermostat will save energy since the thermostat can be
set to a higher temperature when no one is in the house.
1.3
Background
Currently, no commercially available thermostat exists that can detect the presence of a person in
a room, and adjust the temperature based on personal preferences. However, a prototype of a
thermostat controlled by Bluetooth has been made. This prototype uses a computer to send
control signals to a thermostat with a Bluetooth adapter. The thermostat then adjusts the
temperature accordingly [1].
Thermostats are responsible for controlling the output lines that run to the heating and air
conditioning units. When the heat line connected to the air conditioner goes high, the air
conditioner will begin pumping cold air into the room and continue until the line goes low.
Similarly, a heat pump will begin operating when its output line goes high and cease when the
signal is low. A 24 volt AC power line is also connected to the thermostat to provide electricity
to each of the output lines [2]. The desired room temperature is set using a digital input on the
thermostat. The current room temperature is calculated and converted into a digital signal using
a thermoresistor. With these inputs collected, the two are compared and the appropriate output
line (heat pump or air conditioner) is set to the high voltage level. If the temperatures are equal,
then the system has reached its desired state both lines are set low. The surrounding temperature
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is periodically checked against the desired temperature to verify no further conditioning is
needed [3].
Bluetooth devices connect to each other via ad-hoc networks known as piconets. The piconets
are automatically formed as devices come within range of each other [4]. To achieve this
automated device detection, an “enquiry message” is transmitted every 1.28 seconds. One
device will be declared the master and up to seven other devices, known as slaves, can connect to
it. In order to control the transfer of data within the piconet, the master assigns each slave an
address [5]. The physical layer of the Bluetooth protocol operates in the internationally
recognized unlicensed band at 2.4 GHz. Unfortunately, the Wi-Fi wireless networks currently in
use in most homes also operate at this frequency and will interfere with the Bluetooth
connection. To combat interference, the Bluetooth standard defines an adaptive frequency
hopping algorithm that detects other 2.4 GHz communications and attempts to work around them
[6].
2.
PROJECT DESCRIPTION AND GOALS
The adaptive thermostat system will have the following components:

Basic cooling and heating functions

Sensing presence of users

Variable temperature control

Adjusting temperature based on user convenience
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
Displaying current and desired temperature on thermostat LCD
The primary goal of the adaptive digital thermostat is to control the ventilation of commercial or
residential buildings. This ventilation process involves the heating or cooling of a room based on
varying individual preferences. The personal temperature preferences will be associated with the
unique ID of the Bluetooth-enabled mobile phones owned by the occupants of the building. A
digital thermostat will be responsible for executing the ventilating process according to the
unique ID of an inhabitant.
The overall system will include a thermostat, a microcontroller, a Bluetooth enabled cell phone,
and essential hardware to connect these units. The developed thermostat will be comparable in
cost to modern household thermostats. The thermostat will also conserve energy by resetting the
desired temperature to one that requires less energy to maintain when the users have left the
premises.
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3.
TECHNICAL SPECIFICATIONS
Table 1. Technical Design Specifications
Aspect of Design
Bluetooth transceiver range
Number of devices supported
Temperature Control
Cellular Phone
Weight
Voltage Requirements
Current Requirements
Package Size
HVAC Connection (hot and cold lines)
Microcontroller Pins
Microcontroller Word Size
Microcontroller RAM Size
Microcontroller Program Memory Size
Design Specification
30 meters
Up to 7 devices Supported
Adjustable from 60º-80º F, +/- 1ºF
Bluetooth communication capability
TBD
3V
TBD
TBD
24 VAC relay per line
40
8 bits
192 bytes
7168 bytes
The most important factor for the Bluetooth thermostat is the range and the number of supported
users. The thermostat should have a range that allows it to pick up a signal anywhere in the
house, and be able to support enough connections for the maximum number of people that would
be in the house. Both of these factors are dependent on the Bluetooth chip that will be used. To
save energy and satisfy the occupants, the thermostat will have to react fast to temperature
change. Therefore, turning on the system when the temperature rises/falls one degree is
necessary. The thermostat will have to run on a battery power source, so two 1.5 V batteries in
series will provide a voltage of 3 V. Adequate EEPROM storage is necessary for the program.
Initial analysis has shown that 7168 bytes will be sufficient. To store the preferred temperature
associated with each ID, at least 192 bytes of RAM is required.
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4.
DESIGN APPROACH AND DETAILS
4.1
Design Approach
The design will be split up into three subsystems: Bluetooth communication, display with menu
based interface, and control of the HVAC system. These subsystems will all be controlled by a
microcontroller. The Bluetooth communication will be able to receive broadcasted IDs from the
cell phones within the home. The microcontroller will then average the temperature settings for
all of the users and display the adjusted settings on the LCD. The HVAC system will turn on
whenever the temperature varies by one degree from the selected temperature setting. New users
will be able to add preferences into the thermostat by using the menu based interface for the
LCD display.
Bluetooth Communication
The thermostat only needs to sense the presence of up to seven users. So the only required
Bluetooth communication is the thermostat receiving the cell phone users’ broadcasted IDs.
Only using the unique IDs is the simplest way to implement Bluetooth functionality, because
information other than the device’s ID can only be transmitted when the two Bluetooth devices
are paired with a pin number.
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Display
A display will be used to show the current temperature of the room, the temperature setting, the
battery life left for the thermostat, and an icon indicating when the thermostat is connected to
devices. It has two menus, one allowing the addition and removal of new users, and another for
manual override of the controls.
HVAC Control
The HVAC system will be turned on when the temperature of the room varies from the preferred
temperature by 1 degree or more, and will remain on until the preferred temperature is reached.
Because the wiring of the HVAC system deals with much larger voltages than the circuitry can
handle (24 VAC) [2], relays are required to isolate the digital circuitry from the larger voltages
that control the HVAC system.
4.2
Codes and Standards
Since the thermostat is controlling an HVAC system, it will have to follow the standards for
HVAC systems. These standards are mainly for the HVAC system itself and not the thermostat,
so most of the concern is taken care of by the HVAC manufacturer and installer. The few
standards that do deal with the thermostat are concerned with energy saving. Following these
standards will be a priority as energy savings are a major feature of the product.
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The Bluetooth specifications standard will be heavily used within the project. An adapter that
conforms to this standard will be purchased. Cell phones should properly implement the
Bluetooth standard. The standard will be referenced to process the signals that the adapter in the
thermostat sends to the microcontroller.
4.3
Constraints, Alternatives, and Tradeoffs
The main constraints of the design deal with power. Power conservation techniques will have to
be employed since it will be running off of alkaline batteries. Turning off idle electronics and
minimizing the Bluetooth polling delay are the most important features to conserve power.
These features can be implemented by modifying the microcontroller program.
Alternatively, the thermostat can be connected to the house's power supply to eliminate the
power conservation concern. Using this AC power supply could increase the difficulty of the
project, since a voltage regulator would have to be created. Another problem might arise in
implementing the Bluetooth receiver and decoding the device IDs. If the receiver
implementation becomes a problem, a Bluetooth USB stick and a PC can be used for the main
computations of the thermostat, and can communicate with the thermostat by telling it what
temperature is preferred.
Depending on time constraints, some functionality of the thermostat might have to be dropped.
If the menu based interface for the LCD display becomes too difficult and time consuming, the
device IDs can be hard-coded into the microcontroller. With this hard-coding approach, the
microcontroller would have to be reprogrammed whenever a new cell phone is going to be
monitored.
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5.
SCHEDULE, TASKS, AND MILESTONES
Figure 1. Gantt chart outlining project schedule.
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The Gantt chart in Figure 1 illustrates specific milestones for this project. The first major
milestone is the microcontroller program, scheduled for completion on October 14th. The second
major milestone is the project demonstration on December 2nd. The most time consuming
processes are the schematic design of the thermostat and the programming of the
microcontroller. To ensure a smooth integration process, each component will be tested
separately before the final product is assembled and tested. The specific components have been
broken up among our team members:

Trey will be responsible for designing the thermostat schematic.

Scott will be responsible for the website and processing the wireless communications
with the microcontroller.

Jennifer will work on the data entry interface and display.

Mark will be responsible for the assembly of the HVAC controller
Each of these components will rely on input signals from their neighboring components, so
keeping all group members on the same page will be critical. Each member will be responsible
for ordering his or her parts and implementing their design.
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6.
PROJECT DEMONSTRATION
The goal of the project is to have a fully automated adaptive digital thermostat by the end of the
prototype design. Optimistically, we expect the digital thermostat to meet most of its essential
requirements. For the project demonstration, we plan to match specific temperatures on the
thermostat with different Bluetooth id’s on one or more cell phones. Within different users’
proximity to the thermostat, we plan to show the audience the change in temperatures
accordingly without any physical interference with the digital thermostat.
Furthermore, we also intend to make the audience aware of the display readings on the digital
thermostat according to varying temperatures. These various readings will show the adaptive
nature of the thermostat in providing comfort and convenience to its users.
7.
MARKETING AND COST ANALYSIS
7.1
Marketing Analysis
The market for HVAC units and related products has grown steadily over the last 20 years and
continued growth is expected in the future. A study by the Department of Energy revealed that
from 1978 to 1997, the percentage of households in the United States using central AirConditioning rose from 23% to 47% [7]. This study also indicated that households are using
their AC units more often, and not surprisingly, this surge in AC use has led to increased energy
consumption and higher costs of operation. With a growing national concern over energy
conservation and rising annual temperatures, the opportunity for HVAC energy regulating
products is the highest it has ever been.
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Many homes have looked to programmable thermostats as a solution to rising energy costs.
Through a digital scheduler, these units are designed to provide power to the HVAC only during
periods that people are in the room. Units such as the Honeywell 7 Day Programmable
Baseboard Thermostat promise up to a 20% savings on heating and air-conditioning costs each
month [8]. However, to take advantage of these systems a home owner must know when they
will be in the room.
Another trend in the HVAC industry is the use of wireless thermostats, which allow homeowners
to control the room temperature from anywhere in the house. These devices typically cost
around $200 for installation and claim to reduce energy costs by 20% per month [9]. Products
such as the Enernet T9000 Wireless Thermostat have found considerable commercial success
with wealthy residential customers and large commercial venues such as hotels and shopping
centers [10].
No current commercial product on the market will regulate HVAC operation based on the
automatic detection of one’s preferences. Given an increased consumer interest in energy saving
and automation, the production of such a product would find substantial success in today’s
HVAC market. We intend to market our product towards wealthy residential customers who are
concerned about convenience and saving energy.
7.2
Cost Analysis
A cost analysis for the development and production of an automatic thermostat reveals such a
product to be very cost effective. As indicated below, the initial development cost will be very
small relative to the production costs over the next five years. With all factors considered, the
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overall suggested retail price is consistent with the industry average of approximately $200 for
similar products [9].
Development Costs
The development of this product will require the employment of four full-time engineers (recent
college graduates) with a base annual salary equal to the national average of $51,496 [11]. It is
expected that these engineers will need to be employed for 57 hours in order to complete the
design process, and at $28.65 an hour, this will cost $6532.20. The pricing methodology for
these figures is as follows:

Hourly Rate: ($51,496 / year)(1 year/48 wks)(1 week / 5 days)(1 day / 8 hrs) = $28. 65 / hr

Number of Hours: Lectures (15 hrs) + Recitation (22 hrs) + Development (20hrs) = 57 Hours

Hourly Rate ($28.65) * Number of Hours (57) * # of Engineers (4) = $6532.20
Development costs for this product will be limited to the cost of employing these four engineers,
giving a total of $6532.30.
Production Costs
The production costs for an automatic thermostat is based on the retail price of each part required
for construction of the device. We assume the product will be able to store seven users’
preferences. The associated parts costs are as follows:
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Part
Number
Quantity
Total Price
Bluetooth receiver
Eb100-SER
1
$22.00*
Thermoresistor
AD590
1
$6.50
Microcontroller
PIC14000
1
$5.49
Basic Wiring
N/A
N/A
$5.00
Circuit Board
AD100
1
$1.73
Thermostat Casing
N/A
N/A
$3.00
Voltage Relays
Z756-ND
4
$20.20
LCD Display
153-1013-ND
1
$12.36
LEDs
P399-ND
4
$2.64
Total Cost
N/A
N/A
$78.92
*must buy 1000 for this price
The prices are taken from current company catalogs and result in a total expected cost of $78.92
for each unit produced. Note that general estimates were given for wiring and casing which may
be more or less than the actual cost.
Suggested Retail Value
With both development and production costs, it is expected that the total cost of producing n
automatic thermostats will cost $6532.30 + ($78.92 * n). Based on the market analysis for this
product and assuming a vigorous advertising campaign, the expected sales for these units over
the next five years are shown below. Note that the sales are expected to increase each of the first
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five years, due to the increasing demand for energy saving devices and word-of-mouth
advertising.
Year
Sales (# Units)
1
2000
2
3000
3
6000
4
10000
5
11000
These projects estimate that 32,000 units will be sold during the first 5 years. Additional cost
factors that should be accounted for are:
Factor
Total Amount for First Five Years
Assembly Costs
$320,000 ($10 / unit)
Testing Costs
$32,000 ($1 / unit)
Advertising & Marketing
$500, 000
Fringe Benefits
$100, 000
Overhead (Building, Electricity, etc)
$500, 000
Profit Margin (10%)
$ 398,397.23
Total Additional Cost
1,952,000
To produce 32,000 units over the next 5 years, this gives:
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
A total cost of $3,983,972.30

A total profit of $398,397.23

A suggested retail price of $136.95
As indicated in the market analysis, current wireless thermostats retail for approximately $200
per unit. Given the increased functionality of the proposed product and the increased market
demand over the next five years, a suggested retail price of $136.95 is appropriate.
8.
SUMMARY
As of September 17, 2007, we have nearly finished the design phase of the project. We have a
rough schematic of the thermostat with Bluetooth adapter, microcontroller, and LCD display.
We have chosen the necessary parts, as listed above, and are getting ready to order them. All of
the parts will be ordered before the end of the week. At this point we need to choose how to
program the microcontroller so that we can start that soon after it arrives. This is imperative
since the programming of the microcontroller is on the critical path. We don’t anticipate any
difficulties with our parts since they are all sold in the US and are relatively common, with
multiple vendors selling each part.
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9.
REFERENCES
[1]
“ECE 445: Senior Design @ UIUC,” [Online document], [cited 2007 Sep 16], Available
HTTP: https://courses.ece.uiuc.edu/ece445/?f=Projects&sem=fall2006
Ritetemp, “Ritetemp Professional Reference Guide,” [Online document], [cited 2007 Sep
4], Available HTTP: http://www.ritetempthermostats.com/images/ritetemp_Professionalreferenceguide_current.pdf
Shepherd, G. Personal interview. 4 September 2007.
Bluetooth Core Specification v2.1, “Vol. 1: Architecture and Terminology
Overview,” Bluetooth Special Interest Group, 2007.
A. C. Davies, “An Overview of Bluetooth Wireless Technology and Some Competing
LAN Standards,” In Proc. IEEE International Conference on Circuits and Systems for
Communications ‘02, 2002, pp. 206-211.
Bluetooth Special Interest Group, “Bluetooth Basics,” [Online document], [cited 2007
Sep 3], Available HTTP: http://www.bluetooth.com/Bluetooth/Learn
S. Battles, “Trends in Residential Air-Conditioning Usage from 1978 to 1997,”
[Online document], 2000 Jul 24, [cited 2007 Sep 15], Available HTTP:
http://www.eia.doe.gov/emeu/consumptionbriefs/recs/actrends/recs_ac_trends.html
Honeywell Corporation, “Honeywell Programmable Thermostats,” [Online document], [cited
2007 Sep 13], Available HTTP:
http://www.aubethermostats.com/?gclid=CJGxoZrPyI4CFQHgPAod-RyDwA
ToolBase, “Wireless Thermostats,” [Online document], [cited 2007 Sep 13], Available
HTTP: http://www.toolbase.org/Technology-Inventory/HVAC/wireless-thermostats
Enernet Corporation, “T9000,” [Online document], 2005, [cited 2007 Sep 13], Available
HTTP: http://www.enernetcorp.com/products/thermostat.htm
CNN, “Starting Salaries,” [Online document], 2005 Apr 19, [cited 2007 Sep 13], Available
HTTP: http://money.cnn.com/2005/04/15/pf/college/starting_salaries
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
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