Affective Wearable Sensors CDRMarch 8th , 2004

Authored By:

Daniel BishopJosh HandleyPhillip HayChristina HernandezRosy LogioiaGouri ShintriClay SmithAdam Stevenson

Table of Contents

I. Project Information.......................................................................................................... 3II. Design Constraints..........................................................................................................6A. Sensor Constraints..........................................................................................................6Size.......................................................................................................................................8Time..................................................................................................................................... 8Component Availability.......................................................................................................9Power................................................................................................................................... 9462 Considerations.............................................................................................................10C. Software Design Constraints........................................................................................10III. Alternate Solutions Considered ..................................................................................11Sensor Alternatives............................................................................................................ 11Hardware Alternatives....................................................................................................... 11Software Alternatives.........................................................................................................12IV. Proposed Design........................................................................................................ 13Sensor Design.................................................................................................................... 13Software Design.................................................................................................................20V. Updated Validated Testing Procedures........................................................................22Sensor Testing Procedures ................................................................................................ 22VI. Updated Schedule....................................................................................................... 24Sensors............................................................................................................................... 26Hardware............................................................................................................................26VIII. Brief Review of Engineering Standards................................................................... 28

I. Project InformationProject Background

Wearable computers and affective computing is becoming one of the most interesting and

complicated topics of computer human interaction. It involves various fields of study,

such as computer science, psychology and physiology. Even though the literature on the

subject is still at its primal stages, many projects are underway to discover the link

between psychological states and physiological responses of the human body.

The goal of affective computing is to decipher if our brain processes an emotion before

the physiological response or vice versa and therefore we are searching to determine if the

emotion is experienced before the physiological change or if the physiological response is

translated into an emotion by the brain. Psychologists first looked into the subject and

many clashing theories were formulated.

Recently, computer scientists added themselves to the mix when they needed to create

applications to measure the physiological changes in a body. At first, they borrowed

instruments like electromyograms and respiratory sensors from the medical community,

due to their size, but over time through collaboration, smaller sensors have been

developed that can be worn outside of a medical laboratory. Today, a person can

simultaneously wear multiple sensors throughout the day to monitor their physiological

activity.

Today, new problems including wearability plague scientists. Historically, the use of

physiological sensors has been confined to a lab setting since the subjects are usually

covered with multiple wires to register every little change that occurs within their bodies

while they are performing a series of psychological and physiological tasks. This limits

the amount of data that can be collected for data can only be collected while the subject is

present. Therefore, for affective sensor experiments to be expanded and for their

usefulness to increase, the need arises for less intrusive equipment.

Wearable computing is working toward solving this problem by allowing the user to

monitor their physiological responses away from a medical facility by wearing a device to

gather data throughout the user’s daily activities. These computers are designed so that

they can be continuously worn outside of a lab setting while not hampering a person’s

mobility. When combined with affective sensors, physiological data can be collected

throughout the day continuously. Affective wearables are unlike portables for they are

worn, not carried, and are usually in direct physical contact with the wearer, possibly in a

long term intimate way. The devices are similar in regard to ambulatory medical devices,

for both monitor the body’s physiological responses. They can be connected to a belt,

reside in your clothing, or be formed into jewelry to provide an alternative interface

beyond the traditional keyboard and mouse paradigm to track increasingly important

statistics like stress, pulse, and the body’s oxygen levels throughout a persons daily

activities. For example, airplane pilots need to keep track of there oxygen levels when

flying in non pressurized aircraft as do athletes to determine whether they are doing

aerobic or anaerobic exercise. Keeping track of ones pulse would benefit anyone working

out as well as anyone who needs to track their daily stress levels.

To date, most affective wearables have been bulky, and are not convenient to wear. Most

pulse oximeters attach to a finger, and either have wires going from it to a base station

disguised as a watch, or they are bulky in design and therefore prevent the user from

easily using the hand with the sensor attached. Other sensors are designed so that they

can be worn on a foot, or attached to an earlobe. Both of these designs suffer problems if

the wearer wants to be active beyond walking for blisters can form on the foot and

anything attached just to the earlobe is prone to falling off if the wearer has to jog or run.

Last, most sensors usually have wires connecting the sensor to a display or power source.

This raises questions concerning extended wear and mobility, since the wires can be

snagged, or hinder the wearer’s movements. Therefore recently there has been a general

trend to move toward wireless affective wearables.

Wireless computing has been a growing trend, and as the chip sizes get smaller and the

power requirements lessen, wireless options become attractive. Past affective wearables

have been designed so that the GUI that user interacts with affective wearable is built in

or directly attached to the wearable by a series of wires. New wearables, including the

MIT blood pressure volume earring project, use inferred communication to relay

information to get around use of wires, but instead rely on a line of sight between the base

unit and the affective wearable.

Once a user is not restrained in movement by the affective wearable, the next concern

will probably be the aesthetics and comfort of the device. The goal today is to get the

sensor to be as aesthetically and comfortable as possible, usually by minimizing the

circuits size.

Needs Statement

Pulse oximetry has traditionally been used for medical purposes, such as: monitoring

blood pulse and oxygen content while a patient is under anesthesia, and in emergency

situations to help diagnose a patient’s condition. There have also been cases of non-

medical usages, such as in special cases where pilots need to monitor their oxygen

saturation at high altitudes.

Our proposed design is to incorporate the effectiveness of this technology, but extend it to

be used wirelessly. Wireless technology will increase the practical application of the

device. Once the product is completed, possible implementations include activities such

as aerobic exercise, or athletic training. Such implementations will improve the efficiency

of the user’s task.

Goals and Objectives

The goal of our project is to design a device that will measure the blood volume pulse and

the skin conductance of an individual who is undergoing a series of tasks. These

measurements have to be transmitted wirelessly to a computer, which will graph the

information in real time. The tasks for the experiment will be divided into physical and

physiological: from continuous light physical activities to more “brain involved”

activities. The data collected by the device will be sent wirelessly to a computer, which

will display them in real time through a computer graphical interface.

To achieve this overall objective we will proceed through a series of intermediate goals:

1. Define the system, by researching similar projects and technologies.

2. Submit project proposal for feedback.

3. Research key areas: sensors, sensor interfacing, radio transmission, data

acquisition

4. Design and build a pulse oximeter. Pulse oximeter’s are available “off the shelf,”

but they are too large for our needs.

5. Interface the sensor with a RF chip. This includes getting the data out of the

sensor and preparing it for wireless transmission.

6. Radio transmission of the captured data to a base station.

7. Recovering the transmitted data at the base station for input to database.

8. Create a graphical user interface.

9. Test and debug product.

10. Submit completion report and final demonstration.

II. Design ConstraintsA. Sensor Constraints

As described in the project background, the main goals of this project is to create a

wearable device. This implies that the device must be sufficiently small to comfortably

wear on the hand. To that end, we have been faced with several size limitations and

constraints.

First we must be able to power the device from a battery. This constraint has greatly

affected our choice of electronic devices. For instance, our original choice of OP AMP

for the signal filter required a 15V input, obviously much larger than a small battery can

supply. So we searched and found another model that requires less than 5V input and

achieves the same functionality. We have ordered batteries of several different voltage

output values to power the various parts of our design, to give us the most flexibility in

power and size constraints.

We have built and tested prototypes for the pulse and temperature sensors on the

breadboard. These circuits are too large to directly implement into our design because of

the size constraints, so we have chosen to have the prototypes mounted onto a PC board.

These smaller circuits can then be easily be used as a wearable device on the hand.

One of the early problems encountered was the unusually large amount of noise in our

sensor detecting circuit. There was a constant signal at 60 Hz that completely covered the

desired output pulse signal. Our initial solution was to design a low pass filter to mute

everything above 5 Hz, since our desired signal was between 0 and 2 Hz. Although our

tests indicated that our filter was working properly, we continued to get an unacceptable

amount of noise. We then implemented a second order low pass filter in order to get a

steeper cut-off value.

Also, it should be noted that our sensors are very sensitive to movement and positioning

of the device on the hand. Thus special care must be taken to insure proper placement of

the devices, or the output data may be invalid.

From a medical standpoint the pulse sensor we are working with is a federally regulated,

prescription only product. So we have had to be particularly careful when talking to sales

representatives – letting them know that their product will be used only for research

purposes.

We have also been faced with the great complexity of reverse engineering an electrical

system for which we previously knew little about. From our initial research and

consultation with biomedical engineering faculty we hypothesized that our circuit

contained a LED and a photo-detector. Our testing has confirmed our hypothesis. For a

detailed explanation of the circuit including schematics, see the proposed design section

of this document.

We believe that our project can meet all of the size restraints reasonably well.

B. Hardware Constraints

Size

In order for the sensors device to be wearable on the wrist, the board design cannot

exceed certain size limitations. The board is set at 1.8 inches; therefore all mounted parts

have to be small enough to fit on the board layout. A main goal of the sensors device is to

be light-weight, low-power, and wrist-watch size. In order to meet these goals, the board

layout had to be compact enough to fit on the underside of a watch, which is

approximately 1.5” inches across. The size constraint placed upon the board design team

meant a simplistic design with compact parts. It also meant discarding potions of the

entire design that might have otherwise been mounted onto the board, such as the USB

chip.

Time

1.5”

Transmission Board.

Size = 1.8“

The board must be tested thoroughly before it is sent off for creation. This portion of the

project cycle must be completed quickly so that the board can be sent off to be created.

Since the creation process takes approximately two weeks, it would be most beneficial to

our team to have this being done over the spring break period. Since our team cycle is

under both this time constraint and the time constraint of the semester (May 1), the

optimal project timeline cannot be used. Instead, the final product can only be as accurate

as time allows.

Component Availability

Another issue facing the team is components that are available for the team to use. The

teams is constrained by the price of the components and what is in stock from the various

manufacturers.

Power

One of the major limitations of the of the project is the amount of power available for the

chips and sensors to use. Since the entire project must worn on the arm, the weight of the

power supply matters. Therefore, to keep the weight of the project to minimum and to

minimize how obtrusive the device is to the user, the size, and therefore the voltage, will

need to be kept to a minimum.

Software

The Chipcon CC2400 requires a solid ground plane on the second layer of the board to

help eliminate interference. Because of this, a four-layer board is required to route all the

pins. The version of Eagle Layout Editor in the 217 lab is a demo version and can only

create a board with two layers. Dr. Liu has the full version of Eagle in his office and so

we used that version, Eagle Layout Editor 4.09.

Pins Available

The Cygnal processor has 32 data I/O bits available to interface with different devices.

There are 13 pins that connect directly to the Chipcon CC2400, which leaves 19 pins.

There are 3 jumper settings: Enable, Digital/Analog, and Transmit/Receive. The Enable

pin will signal the micro-controller that it should get the CC2400 ready to transmit or

receive. The Digital/Analog pin allows the user to choose to take analog input or digital

input and output. The Transmit/Receive pin tells the micro-controller whether to transmit

or receive. This leaves 16 pins the micro-controller has left to interface with. We chose

to limit the number of available user pins to 8 for two reasons. One, there is only 8

analog channels and therefore no more than 8 are needed for analog data; and two, to

minimize the size of the board a minimum number of pins is required, since pins take up

a large amount of space. This leaves 8 data I/O pins that the micro-controller is not using.

462 Considerations

Dr. Jyh-Charn (Steve) Liu, Associate Professor at Texas A&M University, has offered to

purchase the board parts and creation for our team. After our project has been completed,

Dr. Liu wants to use the board as part of his Microcomputer Systems course curriculum.

Therefore, the board layout must meet our project requirements and his specifications as

to be useful for his course. The board cannot include parts not specified to Dr. Liu during

our initial arrangement. These include the Chipcon 2400 and Cygnal Microcontroller. The

board must have the ability to work with both analog and digital inputs.

This constraint means that all other portions of the project, whether or not they meet the

size requirement, cannot be placed on the board without the permission of Dr. Liu. This

requirement also complicates the overall size requirement since the parts that cannot be

mounted on the board are an addition to the overall size.

C. Software Design ConstraintsThe software is constrained by the hardware being used by the circuit board design and by

the target operating system – Windows XP. As for communication with the PC, since we

are not using UART for communication with the serial controller, we can utilize a UART

USB communication device or FIFO USB device.

III. Alternate Solutions Considered

Sensor AlternativesOur initial decision was whether to build our own sensors form elementary parts (e.g.

diodes, resistors, capacitors, etc.) or to purchase commercially available devices. The

advantage of building our own sensors would our detailed understanding of how the

circuit operates including input and output signals. The disadvantage would be the extra

time involved in building and testing our homemade circuits.

If we bought the sensors from a supplier, the technical aspect of assembling the parts into

a reasonably small wearable device would already be done. However this would be at the

cost of our knowledge of the detailed workings of the product.

Our team decided that time and size constraints were a priority so we opted to purchase

sensors form a supplier. As we investigated this “black box” it became apparent that we

didn’t fully understand the detailed working of the sensor. Our final implementation

included a compromise between these two options. We kept the LED and photo detector

of the commercial sensor because their small size fit our constraints. However we built

our own detection and filtering circuit to capture and clean the signal for input into the

micro-controller. See schematics for details of our circuits.

Hardware AlternativesWe had the option of putting everything possible onto the board or only the Cygnal

micro-controller and Chipcon 2400 transmission device. We made the decision to only

put the two main parts needed (micro-controller and transmission device) for several

reasons: post project considerations, size constraint, and power constraint. The more parts

mounted onto the board would mean a higher power requirement in order to run the

board. We also run the risk of needing a larger board to encompass all the parts, which

would not meet the size requirements stated in our goals. The additional parts also do not

follow the agreement made between our team and Dr. Liu, who is funding a portion of the

project cost. It is for these reasons that we decided to limit the board to only the micro-

controller and transmission chip.

Software AlternativesThe team has discussed using parallel, serial or a USB device for communication with the

computer.

IV. Proposed DesignSensor Design

Our team obtained samples and found parts to start building our sensors.

As for the temperature sensor we built a thermometer by using a thermistor and

wheatstone bridge circuit. We provided a 5 volt power supply, used a 10kΩ thermistor,

three 12 kΩ resistors and a potentiometer (variable resistor). We first measured the

thermistor’s resistance which amounted to exactly 10.8 kΩ; we added a couple of kΩ to

figure out the values of R1 = 11.88 kΩ, R3 = 11.8 kΩ and R4 = 11.82 kΩ. We then used

the potentiometer to balance the bridge with a value of R2 ≈ 1 kΩ. The idea of the

wheatstone bridge is to balance its voltage so that V1=V2, therefore Rt+R2 = R1=R3=R4

(see schematic below). We used a digital thermometer to verify our results: we first

figured out that at the room temperature of 75F we had a differential of .073 volts which

we used to calibrate our measurements. We knew our digital thermometer ranged from

86F to 112F; we then warmed up some water in a cup to reach that maximum

temperature. We enveloped the thermistor in small plastic bag

to make sure it didn’t get ruined; we then started to take

measurements at regular intervals with both our digital

thermometer and the voltmeter until the water cooled off to

about 86F.

Temperature V2-V1111.2 0.839108.5 0.599107.2 0.58106.4 0.565105.9 0.559104.2 0.547102.9 0.534101.7 0.52100.9 0.51100.2 0.49599.1 0.47597.9 0.45797.4 0.44796.5 0.43295.8 0.41895.3 0.40594.3 0.38794 0.377

93.2 0.36292.2 0.34791.8 0.33391.3 0.32190.6 0.30690.3 0.27290.1 0.293

We obtained the following results:

The equation we obtained with Excel was derived by:Temperature = (slope) * (V2-V1) + intercept, which we tested:

ThermometerPositions

TemperatureF

MeasuredVoltage V

CalculateVoltage V

% Error

Gouri’s palm 91.6 .314 .314 0Zach’s palm 97.2 .442 .431 2.55Di’s palm 96.4 .403 .414 2.66

Di’s fingers 94.995.9

.340

.360.383.404

11.2210.89

From the preliminary testing we have been doing on the sensors we have decided that thetemperature sensor’s best location to measure skin temperature is the palm of the handbecause the measurements seem to be more accurate and also it will be much easier toposition the thermistor in the right way.The next step will be to reduce our power supply and verify that we can still obtain usefuland accurate readings; once we reach that stage than we should be able to power thesensor with a flat battery and to encase the thermistor and resistors in a board or velcro ofabout 1.5”x1.5”.

We started reverse engineering the pulse Oximetry sensor, and the main problems we

encountered deal with amplification of the signal and filtering of the noise coming from

room lights and power supplies. The sensor is very sensitive to the 60Hz frequency and to

movement so we had to test each part of the circuit with a sine wave generator and power

supply and observe both input and output waves on the oscilloscope. We repeated the

same procedure while attaching each part together. This part took the longest mainly

because we had to do a lot of trial and error because of the three different power supplies,

adjustment of the resistor’s values and sensitivity of the signal. Once we were sure that

our overall circuit was correct we hooked up the Nellcor sensor and observed the output

wave on the oscilloscope. We had to be in the range of 1 volt and 1-2 seconds on the

oscilloscope, do AC coupling , and monitor the output frequency (FFT) to be able to

obtain a useful output. We still had peaks of 60 Hz on the screen and the wanted 1 to 1.67

Hz signal was visible, but very weak. We also verified that a better signal was received by

positioning the LED and detector at almost opposite sides of the finger so that the light

source would bounce off the bone into the detector and not shining through the bone.

To be more specific our circuit is made of the following:

Light source : 1.5-volt supply connected in series with 50Ω resistor and theinfrared LED;

Detector : this part consists of three subparts in series with each other:

1. Photo-voltaic detector: an amplifier circuit, which uses a 741Cn opamp

hooked up to the diode detector in its inverting and non-inverting inputs,

which then is in series with a 10MΩ resistor. This amplifies the weak

microamperes current detected.

2. Unit Gain: a non-inverting opamp. This is used to avoid the higher

impedance of (1) will draw all the current from (3).

3. Low Pass 1st Order Filter: a 741CN opamp with 330Ω resistor for the

inverting input in series with a 3300kΩ resistor, which is in parallel with a

10µF capacitor. This provides an extra gain of 10 volts and cutoff

frequency of 5Hz and 20dB decay per decade.

The next steps will be to eliminate the unit gain, use a second order low pass filter to

obtain a 40dB decay per decade or more, cutoff the frequency to 3Hz and utilize an

opamp which will require a lower power voltage. As mentioned before we currently have

four parts to it that require at least two power supplies. We have tried to light the LED

with a 1.5 volts battery, and this gets hot, so we are looking into battery holders.

We just received the galvanic skin sensor; we believe we simply have to run a very low

power supply through the sensor heads and measure the resistance coming off the sensor

wires. The snap on jelled sensor are designed to adhere to the skin and reduce the risk of

feeling the small current running through. They will be positioned on the second phalange

of the fingers at opposites ends, so the all sensor on the finger will be not bigger then

their size , approx. 1”x1”. We will have more conclusive data available for the next

report.

All the sensors will receive a voltage input from a battery. The general idea is to put the

actual sensor on the hand and move batteries and extra parts on the wrist, probably on the

opposite side of the transmitter.

All the outputs will be analog signals, so we need to make sure that the microcontroller is

programmed to recognize our signals and use it’s A/D to transmit correctly to the

receiver.

In terms of the power requirements for the project, we need to verify that our amplifier

use a low voltage supply. In testing, our pulse oximetry circuit is mounted on a powered

board that feeds 15 volts to the opamp. We will use 5V opmap for the implementation

version of the design. As for the other circuits we shouldn’t encounter similar difficulties.

We will also use the shielding provided by the sample sensors we were able to obtain and

we had to incorporate filters to reduce the noise surrounding the sensors.

We are utilizing free samples obtained from Nellcor, as well as parts obtained from the

open labs in the computer science department and electrical engineering department. The

only expense incurred on so far is to buy the galvanic skin response kit for $80.00 from

Stoelting Co., which specializes in polygraphic instruments ; however, we received more

snap op jelled sensors that we need, so we will try to exchange the excess for more sensor

heads.

Part ListTemperature Sensor: 1-10kΩ thermistor

3-12kΩ resistors1-0/50kΩ potentiometer

Pulse Oximetry Sensor 1 Nellcor Disposable sensor2-741 op amp 1-50Ω resistor1-1MΩ resistor1-10MΩ resistor 3-3kΩ resistor2-300kΩ resistor1-300Ω resistor1-10µF Capacitor2-.1µF Capacitor

Galvanic Skin Resistor 1 Stoelting GSR sensor head 2 snap on GSR disposable jelled sensor

Proposed Hardware Design

Schematic

The schematic is actually very basic. The main reason we were able to complete this

design in the time frame was because the schematics for both evaluation boards were

published. Each board contains a crystal, several capacitors, inductors, and resistors,

power, and input output pins. All electrical specifications were published as well as the

decoupling circuits, capacitor, inductor, and resistor values. Our schematic combines

these two evaluation boards onto one small board, 1.8”x1.8”. Our design allows for both

a battery and a dc power source to power the board. All the non-power/antenna pins on

the Chipcon are connected to the digital I/O pins on the microprocessor. This allows the

microprocessor to fully utilize the power of the RF transceiver. Only four pins are needed

to control the Chipcon in its simplest mode.

PCB

All pins, chips, RLC devices, and power devices are placed in an optimal layout position,

which depends on the wires that connect the device. Because the pins on the

microcontroller are quite randomly assigned, the layout of the schematic cannot resemble

the layout of the PCB.

Board Schematic

PCB Board Layout

Software DesignPhysical Connection of the Boards

Each Chipcon evaluation board board contains an RF transmitter/receiver, which isdirectly plugged in to the board.

One of the Chipcon boards is connected to the Cygnal MCU with jumper wires on the I/Opins. The MCU is then connected to the PC’s serial port with a ribbon cable and serialadapter.

For testing of communications with the PC, a signal generator is connected to the analoginput pins of the Chipcon board in place of the sensors.

Sensor Data Conversion

The A/D converter converts the analog input from the sensors to a numeric value, whichthe microcontroller converts to a millivolts value, which is transmitted to the computervia the serial port.

For the temperature sensor, this voltage is linearly related to the temperature, and thesoftware will perform the conversion based on the function described in section.

For pulse rate measurements, we are interested in the frequency (in beats per minute) ofthe peaks of the output from the pulse oximeter; each cycle of high and low voltagereadings represents a heartbeat. To measure this frequency, the software on the PC willinclude a queue containing the last few seconds of readings, and will measure the timebetween the most recent peaks of the voltage readings.

Software Front-end

The GUI on the PC will display real-time readings of body temperature and pulse rate, inthe form of a line graph. At the user’s request, the program will save a reading (alongwith the current date and time) to a file so that readings made at different times can becompared later.

Cables and Attachments (to add to the parts list)

Serial cable for interfacing with the PC Serial adapter Ribbon cable

V. Updated Validated Testing Procedures

Sensor Testing Procedures

Currently, to test the pulse oximetry sensors, we are using an external power supply to

power the LED. The photovoltaic circuit is powered using a 15V power supply that is

built into the breadboard. When everything is powered, the LED is shone into the

photodiode. The photovoltaic detector circuit converts the current into a voltage and

passes it onto the unit gain amplifier circuit, which directs its output to the first order low

pass filter. The output of the low pass filter is connected to the oscilloscope, which

displays the waveform generated by the LED being shone into the photodiode. The figure

below is a block diagram of how these parts are wired together.

External Power Supply

LED Circuit

Photovoltaic Circuit

Oscilloscope

Light is shone into the

photodiode

This power supply powers the LED at

1.5V

Unit Gain Amplifier

Circuit

Low Pass Filter Circuit

The amplified and “noiseless” waveform is

displayed on the oscilloscope

The amplified and inverted waveform is sent to the filter

Current is converted to voltage and is sent to

unit gain amplifier

The temperature sensor is presently being powered by an external power supply. A

voltmeter is being used to measure the voltage difference between V2 and V1. The figure

below is a block diagram of how these parts are wired together.

Updated Schedule of Planned Deliverables

Schematic and PCB Check

Once a board is printed it cannot be changed. To insure that there are no errors in thedesign Adam, Christina and Clay will each check the Schematic and PCB Layout toinsure that there are no errors. Each person will check each file twice. Such redundancyis needed so that there is no doubt about errors.

AIN0 P3.0 DIO9AIN1 P3.1 DIO8AIN2 P3.2 DIO7AIN3 P3.3 DIO6AIN4 P3.4 DIO5AIN5 P3.5 DIO4AIN6 P3.6 DIO3AIN7 P3.7 DIO2

3.3v DIO1AGND DIO0VREF VREFP1.4 ENABLEP1.5 D/AP1.6 T/R

Power Supply

This power supplypowers the circuit

at 5V.Temperature

Circuit

V2 – V1 wasmeasured using the

voltmeter.

Voltmeter

The sheathed thermistorwas immersed in water

along with a digitalthermometer.

Cup ofWater

VI. Updated Schedule

VII. Updated Division of Labor Responsibilities

Sensors

From CDR onward the sensor team plans to do the following:

Remove the unit gain amplifier circuit because it is an irrelevant circuit.

Replace the low pass filter with a second order low pass filter to remove the 60 Hz

noise. If this does not work, we will work to create either a higher order low pass

filter or a notch filter that will specifically cut out the 60 Hz signal.

Reverse engineer the galvanic skin conductance sensors the same way we reverse

engineered the pulse oximetry and temperature sensors.

Replace all external power supplies with batteries for all sensors.

Condense our bulky circuits into something small and wearable, preferably a two-

layer glove where the sensors and their respective circuits are sewn into the glove.

Connect sensor output to the micro-controller and check for correct readings.

Verify that the end results displayed on the GUI accurately depict physiological

responses.

Hardware

The board design team has the following tasks remaining:

Test / debug board design (3-person) Board Team

Send off for parts / creation of board Board Team

Test actual board for accuracy Board Team

Integrate board / sensor layout Sensor and Board Teams

Test / debug board / sensor layout Sensor and Board Teams

Integrate board / sensor layout with software All

Test / debut total configuration All

Complete final product All

Of these tasks, all members of the board design team (Christina Hernandez, Adam

Stevenson, and Clay Smith) will be equally involved. The reason for this decision is

because the testing portions of the project cycle are so important that each person is

needed to double check all work.

VIII. Brief Review of Engineering Standards

Societal Analysis

Affective wearables have a medical benefit to society: They provide an easy, painless way

for people to monitor health complications.

Safety Analysis

The safety risks we have identified are:

•Electric shocks from the sensor. To help prevent them, the sensors will be powered onlyby batteries and never by a wall socket.•The radiation produced by the RF system. However, due to the low power consumptionof the transmitter, we believe that the effects will be negligible.•The possibility that the wearer will be cut by the sensor. To minimize this risk, we willensure that all sharp corners will be removed from the sensor.

Environmental Analysis

Our hardware contains at least two toxic chemicals: lithium (in the batteries) and lead (inthe solder). TODO: Mention any that are in the sensor itself Proper disposal of thesensor will involve recycling the lead and not incinerating the batteries.

Appendices

Beyond Logic. http://www.beyondlogic.org/.Beyond Logic contains general information about interfacing with the USB

and parallel ports.

Logix4U. http://www.logix4u.net/This site includes tutorials on interfacing with parallel ports in general,

using inpout32.dll to interface with the parallel port, and information on creatingdlls for windows.

Silicon Laboratories. http://www.silabs.com/Silicon Laboratories sells small multi-purpose microcontrollers and related

products needed to interface with them. We are using Silicon Laboratories topurchase two C8051F015 mixed-signal microcontrollers.

Affective Computing Research Areas. http://affect.media.mit.edu/AC_research/MIT Media Laboratory has several projects involving affective computing.

The most pertinent of these is the affective jewelry research project. They havedeveloped jewelry which measures human physiological signals.

Laipac. http://www.laipac.comLaipac sells GPS and wireless technology. We are using Laipac to

purchase TLP/RLP 434A wireless transmitters and receivers.

Golledge Electronics Frequency Control Products. http://www.golledge.com.Golledge sells frequency control products such as oscillators and crystals.

We are using Golledge to purchase a GXO-U102 oscillator.

Axelson, Jan. Parallel Port Complete: Programming, Interfacing & Using thePC'S Parallel Printer Port. Independent Publishers Group.

This book is a reference for using the parallel port. In addition, it includesseveral examples of projects done using the parallel port, including one thatinterfaces with analog sensors.

Picard, Rosalind. Affective computing. MIT Press. Cambridge, Massachussets.1997.

This book includes much information on the theory of affective computingand the conditions needed for it to be successfully put into practice.

Techniques in Psychophysiology. Edited by Irene Martin and Peter Venables .John Wiley & Sons, c1980. QP360T4.This book includes techniques for psychophysiological measurement of

human subjects. It is useful in determining the operation of the sensors.

Fundamentals of wearable computers and augumented reality. edited byWoodrow Barfield and Thomas Caudell. Electronic resource. LawrenceErlbaum Associates. Mahwah, NJ. 2000.

This book examines the ideas and technologies necessary to moreclosely bond humans and computers by using wearable computers.

7th International Symposium on Wearable Computers. IEEE online resource.October 21-23, 2003.Topics at this symposium included applications of wearable computing,

hardware involved with wearable computing, human interfaces, socialimplications, and the future of wearable computing.