thermoelectric peltier heating shoes

Thermoelectric Peltier Heating Shoes

Team: 49

Mock Design Review ECE 445

Spring 2015

TA: Kevin Chen

Group Members: Xun Chen

Gilbert Lityo Shuli Huang

Table of Contents

1. Introduction 1.1 Project Overview 1.2 Objectives

1.2.1 Goals 1.2.2 Functions 1.2.3 Benefits 1.2.4 Features

2. Design 2.1 Block Diagram 2.2 Block Descriptions and Schematics

2.2.1 Thermoelectric Peltier Pads 2.2.2 Protection Circuit 2.2.3 Lithium-ion Battery 2.2.4 Heating Module 2.2.5 Microcontroller 2.2.6 Bluetooth Modem 2.2.7 Android App

2.3 Power Budget Analysis (Calculation) 3. Requirements and Verifications

3.1 Performance Requirements and Verification 3.2 Tolerance Analysis

4. Cost and Schedule 4.1 Cost Analysis

4.1.1 Labor 4.1.2 Parts 4.1.3 Grand Total

4.2 Schedule 5. Safety Statement and Ethics

1. Introduction 1.1 Project Overview There are many passive ways to heat up the feet, such as wearing thicker socks or furry shoes. However, this method relies on the heat of the body to keep the feet warm and it is usually not enough in colder climates such as the state of Illinois during the winter. There needs to be a convenient way to actively heat up the feet.

There are such active feet heaters such as pads and insoles, but they all run on limited battery life that needs to be charged after every use. Most of these heaters are not smart, meaning they lack controls that allows the user to change and keep track of the temperatures in their shoes. Ultimately, our group wants to create a shoe that uses the temperature gradient of inner and outside temperature of a shoe to generate renewable energy. Using the generated electricity, we can actively heat up the shoe with a heating pad. A microcontroller and a bluetooth modem will also be available to communicate with a phone to give the user a pleasant experience in controlling the heating.

1.2 Objectives

1.2.1 Goals The goal of this project is to design a smart and green heating mechanism for a shoe. It should be safe, convenient to use and durable. We will need to overcome difficult design challenges such that it can marketable and performs well in general winter environments.

1.2.2 Functions Using a Thermoelectric Peltier Pad, we can generate energy using the difference of temperatures on the two sides of the pads to produce power. We will use the temperature difference between the inside and outside of the shoes to produce a small amount of energy. We plan to use an ultra low-voltage step-up transformer to provide our heating system enough power to turn on the heating pad as well as the microcontroller. The generated power will then be stored in a rechargeable lithium ion battery while the heating pad is not in use. The heating pad is turned on by a switch that can be controlled with the microcontroller. The produced energy from the peltier along with power given by the battery, will be transferred directly into the heating pad when it is turned on.

The heat generated can be used to keep the temperature constant on the inside of the shoes so our thermoelectric generator can keep generating electricity. The battery will also power our microcontroller which will interface between a bluetooth modem that will communicate with an android phone. It will transfer information about the battery and temperature of the shoe to our android app, which in turn the user can view and use the phone to control the shoe temperature.

1.2.3 Benefits - No need to manually switch or recharge battery - Environmental friendly

- Energy depends on outside temperature. Operates better in colder environments - Smart controls over heating and power management - Can be charged whenever the user slips on the shoe

1.2.4 Features - Bluetooth communication with android phone - Complementary Android App - Low power consumption - Temperature sensing - Temperature control

2. Design 2.1 Block Diagram

Figure 1. System Block Diagram

2.2 Block Descriptions and Schematics

2.2.1 Thermoelectric Peltier Pads The peltier pads use the Seebeck effect to convert a temperature difference between the top surface and the bottom surface of the pad into electricity. We plan to use 3 to 5 of 40mm x 40mm x 3.6mm peltier pads to fully cover the inside of the shoe. The power generated will be stored into the Lithium-ion battery to supply power for other parts like microcontroller, bluetooth and heating module.

Figure 2. Thermoelectric Peltier Device Model

Since the output voltage of thermoelectric generators (TEGs) is considerably small, we also attach a step-up converter (LTC 3108) which can boost the output voltage of the peltier pads to a magnitude around 2-5 V depending on the input signal to VS1 and VS2.

2.2.2 Protection Circuit The protection circuit protects the Lithium-ion battery from being over-charged or over-discharged so that the battery will not be drawn too much current and therefore have a longer battery life time. One possible option for the protection circuit is the LTC4070 which can operate at a very low current (450nA).

Figure 3. Power Supply Module

2.2.3 Lithium-ion Battery The Li-ion batteries serve as the power supply for the circuits of heating module, microcontroller and bluetooth modem. They are charged by the voltage produced by the peltier pads all the time, even when the heating elements are not in use. Also there will be a DC to DC converter to scale the output voltage to be compatible with the devices. The Li-ion batteries is able to provide at least 3W of power.

Figure 4. Lithium-Ion Battery Charging Characteristics

2.2.4 Heating Module The heating module we use is a heating pad that uses a mesh of Polyester filament and Micro Metal Conductive Fiber folded into a protective Polyimide Film. The heating pad will be attached to the bottom of the inside of the shoe. There will be a temperature sensor near the heating pad to transfer the temperature data to the microcontroller and help fulfill the idea of controlling temperature from an android app.

2.2.5 Microcontroller The microcontroller we decide to use is PIC 18F2610 because it is featured by its ultra-low power applications and relative simplicity of integrating it in the PCB. It receives the temperature signal from the temperature sensor and sends the data to the phone via bluetooth transmitter. The microcontroller will be programmed to monitor the temperature inside the shoe and control the power delivered to the heating pads according to the temperature preference set by the user on the android app.

Figure 5. Microcontroller Logic Flowchart

2.2.6 Bluetooth Modem The bluetooth modem we plan to use is BlueSMiRF Gold also because of its low power applications. It receives temperature data and battery conditions from the microcontroller and sends them to the android app through wireless connection. It also receives the commands done on the android app and sends them to the microcontroller to control the work of the circuits in the shoe.

Figure 6. Bluetooth Modem Logic Flowchart

Figure 7. Whole Circuit Schematic

2.2.7 Android App The android app will take in temperature sensor’s data transmitted from the bluetooth to display it to the user. The user can then analyze the current temperature of the shoe and use the application to remotely change the temperature of the shoe using up and down buttons.

Figure 8. Android App Software Flowchart

2.3 Power Budget Analysis (Calculation) After testing with a peltier pad in the senior design lab, the peltier pad is0mm x 40mm x 5mm4

producing and (12 ohm resistance)with touching one side of the pad with hand palm. The0mV5 mA5

temperature difference is around 7 degree Celsius.

50mV mA 0.25 mW * 5 =

The Lithium-ion battery is rated with 3.7V nominal operating voltage and 200mAh. We need:

00mAh 0.20556mWs 0.25mW2 * 3.73600 = <

Assuming no energy is lost during charging, we can efficiently charge the one battery with one peltier pad. Even at a temperature difference of 7 degrees is sufficient for charging a battery. Therefore, in actual application where the temperature difference between foot and ambient temperature during winter is above 20, the power is very efficient in charging the Li-ion battery. There are 3 parts that need power supply:

I. Microcontroller The operating current of PIC18F2610 depends on the operating voltage, frequency and mode. Since the Lithium-ion battery provides 3.7V nominal output voltage, we use the ratings of 3V in the datasheet for the calculation. We also use the data for 31kHz oscillating frequency for power considerations. During RC_Idle mode, the MCU operates at 11uA.

1uA V 3uW1 * 3 = 3

During RC_Run mode, the MCU operates at 60uA. 0uA V 80uW6 * 3 = 1

These power consumption are reasonably small compared to the battery capacity. II. Bluetooth Modem

It operates at and in normal mode.3V3 0mA3

.3V 0mA 99mW3 * 3 =

Although it’s big but the modem only drains power when the microcontroller or android app commands it to. III. Heating Pad It operates at and during heatingV5 00mA 6

V 00mA 3W5 * 6 =

the Li-ion battery is rated to have 6W max output so this is fine.

In conclusion, the power budget is reasonable for our heating shoe design.

3. Requirements and Verifications 3.1 Performance Requirements and Verification

Table 1. Performance Requirements and Verifications

Requirements Verification Points

1. Peltier Pads a. The Peltier pads can generate power at a rate of 5.4 mW at a temperature difference of0%± 2

20-30 degree Celsius.

1. A DMM will be used to measure the output of the peltier pads. a. Set the temperature difference to be 20~30 degree Celsius and connect the peltier pad to a 12 ohm resistor. Measure the current and voltage across the resistor to see if the output power is comparable to the theoretical value.

0/10

2. Step-up Converter a. The LTC3108 module can step-up the voltage generated by the peltier pads to 3.3 V at the.2± 0

output pin.

2. A DMM will be used to measure the output of the step-up converter. a. Connect the output pin of LTC3108 to a voltmeter and measure the output voltage.

0/10

3. Lithium-ion Battery a. The Li-ion battery has a capacity of 200mAh each and outputs voltage of 3.7V when.2V± 0

fully charged. b. The battery needs to be able to power up the heating pads c. The battery can be fully charged from empty using the power generated by the peltier pads within 4 hours hour.± 1

3. A DMM will be used to measure the voltage, current and capacity of the battery. a. After charging the battery to its full capacity, connect it to a 12 ohm resistor to measure the voltage and current across the resistor and calculate the total power dissipated after the battery runs out. b. After charging the battery, connect it to the heating pads to see if the heating pads can be powered. c. Try to maintain a fixed temperature differential between the peltier pads and measure the time it takes to fully charge the battery.

0/20

4. Microcontroller a. The microcontroller can send signals to the

4. An oscilloscope and a switch will be used to measure the output from each pin of the microcontroller

0/10

heating circuit to turn it on or off. b. The microcontroller can run the program from the user and output the correct results. c. The microcontroller can communicate with the bluetooth module and the temperature sensor. d. The microcontroller can set the temperature of the heating pads according to the user input.

a. Power on the microcontroller, then connect the logic output to a relay, and see if the relay can operate correctly. b. Connect the microcontroller on a debug kit, run the program and then test the outputs of each pin. c. Transmit and receive the data from the bluetooth module and temperature sensor, test the outputs of the connected pins. d. Read the temperature of the heating pads using the temperature sensor, verify it with the input.

5. Heating Pads a. The heating pad can automatically start heating when the microcontroller turns it on using digital switch. The user can feel obvious temperature increase after 3 minutes 1minute.±

5. A thermometer is used to measure the temperature of the pads. a. Set a sample temperature and test if the module starts heating.

0/10

6. Temperature Sensor a. The temperature sensor can sense the correct temperature and send it to the microcontroller to process

6. A thermometer is used to compare the result of the temperature sensor. a. Read the temperature from the android app and see if it is close to the correct temperature sensed.

0/10

7. Bluetooth modem a. Bluetooth module is able to relay temperature data with phone

7. An android phone with bluetooth is used to detect and pair/connect with the bluetooth module. a. We will check the Bluetooth connection by seeing if it can bind with phone.

0/15

8. Android Application a. Android app is able to receive bluetooth data, and display the correct temperature data and as well as send signals back to the bluetooth module.

8. An android phone with bluetooth is used to set the temperature and a thermometer is used to read the temperature. a. We will use a thermometer to measure the temperature of the heating pad and compare it with the data received/transmitted by the android app through the microcontroller.

0/15

3.2 Tolerance Analysis The most crucial part of our design is getting enough power from the thermoelectric harvesting devices. Although the power generated by the peltier pads seem promising, there’s a significant drop in power generation efficiency after passing through the step-up converter due to the dissipation inside the step-up converter module. The empirical efficiency of the LTC 3108 has an efficiency of around 33% according to the online resources. In order to increase the power output from the TEG module after converter, we need to carefully design the output capacitances to ensure the charge generated from the peltier pads is more efficiently transferred to the battery. With a capacitor of 220uF at the output pin of LTC3108, we can achieve an efficiency of 33%. In general, we need to carefully design the capacitances in the circuit based on impedance matching in order to get highest possible power output.

4. Cost and Schedule 4.1 Cost Analysis

4.1.1 Labor

Table 2. Labor and Hourly Rate Breakdown

Name Hourly Rate Total Hours Invested Total=Hourly Rate x 2.5 x Total Hours Invested

Xun Chen $40.00 170 $17000.00

Gilbert Lityo $40.00 170 $17000.00

Shuli Huang $40.00 170 $17000.00

Total 510 $51000.00

4.1.2 Parts

Table 3. Parts and Price Breakdown

Item Quantity Price Total Price

Heating Pads(COM-11289) 5cm x 15cm 4 $4.95 $19.80

PIC Microcontroller PIC18F2610 1 $10.00 $10.00

Bluetooth Module(BlueSmirf Gold WRL-10268)

1 $34.95 $34.95

Temperature Sensor(LM35DZ) 2 $5.00 $10.00

Peltier Devices 40mmx40mm 4 $10.00 $40.00

Lithium Ion Battery(PGEB016144) 2 $10.00 $20.00

PCB 1 $50.00 $50.00

1:100 transformer 1 $4.00 $4.00

Resistors and Capacitors 10 $0.40 $4.00

Step Up Converter and Power Manager(LTC3108)

4 $5.00 $20.00

Battery Protection Circuit(LTC4070) 4 $3.14 $12.56

Heat Sink 4 $4.00 $16.00

Shoes 1 $10.00 $10.00

Total $251.31

4.1.3 Grand Total

Table 4. Total Price

Section Total

Labor $51,000.00

Parts $251.31

Grand Total $51,251.31

4.2 Schedule

Table 5. Schedule and Tasks

Week Task Responsibility

9 Feb

Finalize proposal Gilbert Lityo

Finalize proposal Xun Chen

Finalize proposal Shuli Huang

16 Feb

Design the schematic for microcontroller and itsinterface to bluetooth module, temperature sensor and heating module. Prepare for Mock Demo

Gilbert Lityo

Design the flow chart, input/output for the microcontroller and start working on the microcontroller programming. Prepare for Mock Demo

Xun Chen

Design the schematic for the peltier pad, battery and power supply. Prepare for Mock Demo

Shuli Huang

23 Feb

Design review, soldering assignment, and start building and testing temperature control system circuit

Gilbert Lityo

Design review, soldering assignment, and implement program on the microcontroller and verify output

Xun Chen

Design review, soldering assignment and start building and testing power system circuit

Shuli Huang

2 March

Integrate and test microcontroller, temperature sensor, heating pad and bluetooth modules

Gilbert Lityo

Start creating Android App. Xun Chen

Integrate and test battery charging, battery protection circuit, step up and step down dc converter

Shuli Huang

9 March

Solder the components of heating module on PCB, check connections and debug circuits

Gilbert Lityo

Communicate App. with bluetooth module, microcontroller, temperature sensor and heating pad

Xun Chen

Solder the components of power circuit on PCB, check connections and debug circuits

Shuli Huang

16 March

Integrate the entire system, make sure that the entire heating module works with the battery supplied by the peltier device

Gilbert Lityo

Improve user interface for the App. Xun Chen

Design the shoes to get an optimized output for peltier devices inside the shoes

Shuli Huang

23 March

Spring Break Gilbert Lityo

Spring Break Xun Chen

Spring Break Shuli Huang

30 March

Individual project report, finalize the PCB and determine the placement for the PCB on the shoes

Gilbert Lityo

Individual project report, start making final presentation

Xun Chen

Individual project report, modify the shoes and place the peltier devices inside the shoes

Shuli Huang

6 April

Prepare for Mock Demo Gilbert Lityo

Prepare for Mock Demo Xun Chen

Prepare for Mock Demo Shuli Huang

13 April

Final test for demo and try to minimize the PCB size Gilbert Lityo

Final test for demo and start writing final report Xun Chen

Final test for demo and modify any updates from Mock Demo

Shuli Huang

20 April

Project Demo Gilbert Lityo

Project Demo Xun Chen

Project Demo Shuli Huang

27 April

Finishing final report Gilbert Lityo

Finishing final report Xun Chen

Finishing final report Shuli Huang

4 May

Submit final report and lab check out Gilbert Lityo

Submit final report and lab check out Xun Chen

Submit final report and lab check out Shuli Huang

5. Safety Statement and Ethics

Our group prioritize the safety and ethical issues regarding our product. For this project, we will follow the IEEE code of Ethics.. Our project process and our final product will adhere to the following relevant IEEE Code of Ethics. Our project is potentially worn by people of all ages and many different locations. Therefore, our product must consider the safety, health and welfare of the public; in order to protect the users of our product. In the process of designing our product, we research on the materials that we are planning to use and we ensure that all the materials used on our product will be safe for the public and to the environment. 1. to accept responsibility in making decisions consistent with the safety, health, and welfare of the public, and to disclose promptly factors that might endanger the public or the environment; The description, data, and design of our project will be honest and realistic. We ensure that all claims and data about our project are based on actual results produced by our product, not fabricated. 3. To be honest and realistic in stating claims or estimates based on available data; We seek and accept honest criticism of our technical work in order to improve our project. Admitting and fixing any errors regarding our work. Also, recognizing and giving credit to those who contributed to our project. 7. To seek, accept, and offer honest criticism of technical work, to acknowledge and correct errors, and to credit properly the contributions of others; To avoid risk of injury to the user, we will ensure that our heating element will not generate high current to raise the temperature of the heating pads above 100°F. 9. to avoid injuring others, their property, reputation, or employment by false or malicious action;

thermoelectric peltier heating shoes

Documents