By: Cody Dunn (Project Manager)

Central Sensor Suite:

Omar Rojas (Systems Engineer)

Stephen Cortez (Electronics Engineer)

Mimy Ho (Manufacturing Engineer)

Seizure Watch:

Robin Yancey (Systems Engineer)

Rose Leidenfrost (Electronics Engineer)

Marena William (Manufacturing Engineer)

Program Objective

Cody Dunn (Project Manager)

The mission objective of the project is to design and implement a wearable sensor suite (A-TeChToP) that allows for the safe and wireless real-time health monitoring of a child between the ages of 5 and 13. A-TeChToP will notify guardians and nearby onlookers when the child’s bio-signals have passed below or above certain thresholds.

The device will help monitor children with histories of

• Asthma Exacerbation
• Frequent Fainting
• Osteogenesis Imperfecta
• Juvenile Idiopathic Arthritis
• Arrhythmias
• Frequent Fevers
• Seizures.

Mission Profile

Cody Dunn (Project Manager)

A-TeChToP will be used by strapping children with the chest and wrist sensor portions of the device. These will then interface with a phone also on the child’s body. Data from the sensors will be sent to a PC or smart phone monitored by the guardian or doctor of the child.

A-TeChToP will be demonstrated by attaching the device to a subject between the ages of 5 and 13. The child will proceed to play outside on a playground for one hour as the team monitors his/her bio-signals. The child will be instructed to perform various exercises and take off one of the sensors to demonstrate the alarm system.

Program/Project Level 1 Requirements

Cody Dunn (Project Manager)

1. The wearable body network must be completed by May 4, 2016, the last day of instruction for E400D in the CSULB Spring 2016 Semester [1].
2. The cost must be limited to $700 [1].
3. The complete body network shall meet ASTM F 963-11 safety requirements [2].
4. The body area network shall be functional for transferring biometric information for a child with the height of at least 1.77 meters (96th percentile height for a 13 year old) [1] [3].
5. “From a full charge, energy allocation and source must provide at least 30.2 minutes of continuous monitoring and data transfer as according to the Center for Public Education’s polled average amount of time allocated to play in public schools” [1] [4].
6. Guardians and doctors shall have the ability to monitor a child’s biological signals wirelessly in real-time using the Arxterra control panel [1].
7. The device shall not hinder the child from completing the California FITNESSGRAM [5].
8. The body network shall measure blood oxygen levels with the stability and accuracy to flag for asthma exacerbation [6].
9. The sensor suite shall measure the body temperature to determine when a fever has occurred [7].
10. Body orientation for the child must distinguish when the child has fallen due to illness from when he/she is upright [8].
11. The device shall accurately measure electrodermal activity such that the detection of grand mal seizures will match that of a traditional electroencephalogram [9].
12. The device shall measure the QRS complex, P wave, and T wave of heart signals with high enough resolution to detect arrhythmias such as supraventricular tachycardia and premature atrial contraction [10] [11].
13. An alarm shall alert the parent and people nearby when one of the child’s biological signals has dropped into a dangerous range [12].

References

[1] R. Goss. (2015, Apr. 1). A-TeChToP Project Requirements [Online]. Available: http://arxterra.com/atechtop-project-requirements/

[2] United States Consumer Product Safety Commission. (2011). ASTM F 963-11 Requirements [Online]. Available: http://www.cpsc.gov/en/Business–Manufacturing/Business-Education/Toy-Safety/ASTM-F-963-11-Chart/

[3] Baylor College of Medicine. (2010). Age-Based Pediatric Growth Reference Charts [Online]. Available: https://www.bcm.edu/bodycomplab/Flashapps/bmiVAgeChartpage.html

[4] Barthe, Patte. “Time Out: Is Recess in Danger?” Center for Public Education. Center for Public Education, 6 Aug. 2008. Web. 19 Feb. 2015.

[5] California Department of Education. (2016). Physical Fitness Testing [Online]. Available: http://www.cde.ca.gov/ta/tg/pf/

[6] G. Parreno. (2014, Nov. 19). Blood Oxygen [Online]. Available: https://www.arxterra.com/blood-oxygen/

[7] H. Medina. (2014, Nov. 19). Temperature [Online]. Available: https://www.arxterra.com/temperature/

[8] G. Parreno. (2014, Nov. 19). Body Orientation [Online]. Available: https://www.arxterra.com/body-orientation/

[9] R. Picard. (2012). EPIBAND: Electrodermal and Seizure Event Alert [Online]. Available: http://www.epilepsy.com/sites/core/files/atoms/files/ST-5-Picard.pdf

[10] American Heart Association. (2015, Oct. 26). Types of Arrhythmia in Children [Online]. Available: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/Types-of-Arrhythmia-in-Children_UCM_302023_Article.jsp#.VsQspvIrKUk

[11] J. Crimando. (1999). EKG Arrhythmia Review [Online]. Available: http://www.gwc.maricopa.edu/class/bio202/cyberheart/ekgqzr0.htm

[12] Galen Carol Audio. (2007). Decibel (Loudness) Comparison Chart [Online]. Available: http://www.gcaudio.com/resources/howtos/loudness.html

Central Sensor Suite

Project Level 2 Requirements

System Requirements

Omar Rojas (Systems Engineer)

1. Bluetooth, IEEE 802.15.1 standard will be used as the wireless method of communication between the Arduino and Android phone due to its simplicity interacting with both the Android phone and the Arduino platform. [1]
2. Android phone and Bluetooth device will not exceed SAR regulation of 1.6W/kg as stated by the FCC [2]
3. Transmission of signals through Bluetooth to Android phone and from Android phone to Arxterra control center shall have a minimal cumulative delay for immediate reaction time. Delay shall be least than a heartbeat (80 beats per min). [3] Source: http://wonderopolis.org/wonder/how-many-times-does-your-heart-beat-in-a-lifetime/
4. The sensors, sensor suite, and android phone shall withstand forces (such as a child falling) of at least 20 Newtons. [4]
5. Electrical components shall qualify as level two water resistance which is defined as “allows for contact with water such as washing hands or light rain. [5]
6. An alert must be sent to the parent whenever vital sign measurements read as “unsafe” (as defined by settings in the Arxterra app).
7. Physiological signals must be clearly presented and updated in real-time on the Arxterra control center.
8. A temperature sensor shall be used to keep track of the child’s body temperature
9. Blood oxygen levels of the child shall be measured through a blood oximeter
10. An accelerometer shall be used to monitor body orientation of the child
11. A pulse sensor shall be used to monitor the pulse rate of the child
12. The heart activity of the child shall be measured through an electrocardiogram
13. Purchases cannot be made for sensors which need to be manufactured before shipping in order to meet deadline requirements.
14. In order for project to stay within budget and meet deadline requirements, no purchase may be made for items outside of the United States.
15. To avoid harming the child, device will not reach a temperature greater than 113°F. [6]
16. The wearable device will avoid using materials that can lead to skin irritants caused by an allergic reaction [7]

References

[1] Standards.ieee.org, “IEEE SA – 802.15.1-2002 – IEEE Standard for Telecommunications and Information Exchange Between Systems – LAN/MAN – Specific Requirements – Part 15: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Wireless Personal Area Networks (WPANs)”, 2016. [Online]. Available: https://standards.ieee.org/findstds/standard/802.15.1-2002.html. [Accessed: 23- Feb- 2016].

[2] Fcc.gov, “Specific Absorption Rate (SAR) for Cellular Telephones | Federal Communications Commission”, 2016. [Online]. Available: https://www.fcc.gov/general/specific-absorption-rate-sar-cellular-telephones. [Accessed: 23- Feb- 2016].

[3] InformationWeek, “FDA Issues Guidelines On Wireless Medical Devices – InformationWeek”, 2016. [Online]. Available: http://www.informationweek.com/mobile/fda-issues-guidelines-on-wireless-medical-devices/d/d-id/1111203?. [Accessed: 23- Feb- 2016].

[4] Hyperphysics.phy-astr.gsu.edu, “Energy of falling object”, 2016. [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html. [Accessed: 23- Feb- 2016].

[5] Prestigetime.com, “Watch Water Resistance information for watches from PrestigeTime.com !”, 2016. [Online]. Available: https://www.prestigetime.com/page.php?water-resistance. [Accessed: 23- Feb- 2016].

[6] Prothermographer.com, “How Hot”, 2016. [Online]. Available: http://www.prothermographer.com/how_hot.htm. [Accessed: 23- Feb- 2016].

[7] ACAAI, “Skin Allergy”, 2016. [Online]. Available: http://acaai.org/allergies/types/skin-allergies. [Accessed: 23- Feb- 2016].

Subsystem Requirements

Stephen Cortez (Electronics Engineer)

17. Bluetooth component will be chosen to be highly compact, no greater than 30mm by 25mm by 20mm, in order to optimize the overall size of the device. Current Candidate for this requirement: Simblee BLE Module RFD77101.

18. Purchases for components will be made in a timely manner as to promote the complete construction of the device and its extensions before the given deadline.

19. In addition to alerting the parent, or other monitoring individual, the device shall alert the proper authorities immediately should particular, measured thresholds be violated for each sensor.

20. The placement of the ECG electrodes shall be tested for on multiple subjects in order to find the optimal location for rejecting electromyographic interference on the arm.

21. Wiring from the sensors to the main housing of the device shall be made for optimal compactness and visibility.

22. All information and signals must be consolidated onto one bluetooth device and then sent to the Android phone for easy communication with the Arxterra website.

23. Batteries used will be capable of properly powering the device for a minimum of 30 minutes.

24. The alert settings on the Arxterra website for the device will be protected by a form of security verification, most likely a numerical password.

25. The pulse oximeter must be capable of measuring specific blood oxygen percent ranges accurately. These ranges include 96% to 98% (since 100% is not reasonable) for regular breathing, 90% to 95% for hypoxemia, and any percentage below for a medical emergency.

Mimy Ho (Manufacturing Engineer)

26. The device can be put in a 3D printing compartment with can withstand with the force of 20N

27. The PCB will be sprayed a waterproof coating to prevent sweat and rain

28. The PCB need to be ordered by the end of March to meet the timeline requirement.

29. The device will be 3D modelling by using Solidwork before manufacturing

Design Innovation

Creativity Presentation

Systems/Subsystem Design

Product Breakdown Structure

Omar Rojas (Systems Engineer)

 

The product breakdowns structure details the sensors and module being used in the ATechTop device.

Electronic System Design

System Block Diagram

Omar Rojas (Systems Engineer)

The system block diagram above shows the flow of how the ATechTop will function. The process begins with the sensors gathering information from the patient wearing the device.The information is the n process by the Arduino which is then communicated via bluetooth to the android phone that will be placed somewhere on the patient. The phone then communicates with the Arxterra control center. The information can then be processed by the receiver which can be a parent or if an alarm is triggered, emergency services.

Interface Definitions

Omar Rojas (Systems Engineer)

The interface matrix above details the connection between the microcontroller and the sensors and other modules being used in the ATechTop device.

Mechanical Design

Stephen Cortez (Electronics Engineer)  (Image) and Omar Rojas (Systems Engineer) (Description)

The Android phone and the Arduino mini pro will be placed on the chest of the child in a specially designed 3D printed case. The sensors will be connected to the Arduino by wires. The sensors will placed in optimal locations that will better suit their readings. The requirements of the sensors will be a power  supply and an analog pin connection to the Arduino, which will be achieved by having the sensors being wired to the Arduino. The subsystems are separated by the sensors to be use:

Temperature: The temperature sensors shall be placed on the chest area to gain a better reading of the child’s core temperature.

Pulse Sensor: The pulse sensor shall be placed on the near the chest, close to the heart, to better read the pulse rate of the child

Blood Oximeter: The blood oximeter shall be placed on the the earlobe to gain better readings of the blood oxygen levels.

Accelerometer: The accelerometer  shall be placed within the housing for the Arduino and Android phone so that it is closer to the center of gravity of the child.

ECG: The ECG shall be placed on the underside of the upper arm of the child to gain better readings of the heart’s electrical activity.

Mimy Ho (Manufacturing Engineer)

Introduction

The  A-TeChtoP wearable design not only predicts the seizure of a child but also provide the improvements in the weight and size of the device. The design shall provide the comfort, safety and shall not limit any physical activities while a child wears it. The device is based on the design’s idea of the Wednesday A-TeChtop Spring 2015, by using the chest straps. However, the new design shall have electrodes to obtain the ECG signal, so the chest harness shall be contact with the skin.

Preliminary Sketches

The figure 1 explains how the wearable device will be expected to look like. There are two adjustable straps: one goes around the chest with about 2 inches width, and other one will go over the shoulder with about 1 inch width.

• On the chest strap, an android phone, accelerometer and Arduino Pro will be placed in the front; the ECG sensor will be placed on the side under the upper arm
• On the vertical strap, the temperature sensor will be place near the heart, the blood oxygen sensor will be attached to the earlobe and wiring down to the Arduino.

Figure 1: Sketch of the chest harness

Figure 2 shows the design shall be look like the NEOpine G-422-R Single Chest Shoulder Strap Mount for GoPro Hero

Source: http://www.dx.com/p/neopine-g-422-r-single-chest-shoulder-strap-mount-for-gopro-hero-2-3-3-black-red-320274#.Vst47fkrLIU

 

Design and Unique Task Descriptions

Stephen Cortez (Electronics Engineer)

The old device portion of the A-teChTop project was designed considering all of the electrical system requirements and specifications as well as the potential sensors that could be used to meet those requirements. It was also important to consider the physical layouts and shapes of the sensors, although adjustments can be made to the housing of the device to meet specific needs.

Initially, the design of the device began with the Android phone since it is the main center of communication with the Arxterra software. Trying to keep mobility and visibility requirements in mind, the Android was concluded to be placed within a secured pouch attached to a strap around a child’s upper-abdominal but wrapping around just underneath the arms. Doing so allows a full range of motion. Next, the Pro Mini Arduino board was chosen to serve as the device’s MCU on the grounds that it is the smallest available microcontroller product that is capable of receiving and transmitting bluetooth data as well as handling the various inputs of all the sensors. The Pro Mini Arduino is also able to be easily programmed with the familiar Arduino IDE software.

After the MCU, the design for the ECG was researched with the intention of not following the conventional chest placement electrodes since this would prove uncomfortable for a child. Rather, the electrodes were determined to be placed on the upper-inside portion of one of the child’s arm (which particular side does not seem to be important), using only two electrodes. This configuration takes advantage of the MCU placement as well as posing the most comfortable for a child to wear and be active. Wiring can be made minimal and short while being concealed underneath as little as a t-shirt. However, using this design will require some extra circuitry that implements filters in conjunction with digital filters within the coding of the MCU in order to cleanse the ECG signal of any undesirable noise, which can easily be generated by the surrounding muscles. Examples for the electrode placement design can be found at the following link:

http://www.saelig.com/supplier/plessey/Aps-Note_291491_Single_Arm_ECG_Measurement_Using_EPIC.pdf

The remainder of the sensors includes the temperature sensor, the accelerometer, the blood oximeter, and the pulse sensor. For the temperature sensor, previous group designs were observed, allowing the current group to decide upon the LM35 precision temperature sensor. In order to obtain heat readings from the core of heat from a child, the LM35 will be placed along with the main device unit at the center chest region, making sure to maintain either direct skin contact or close skin proximity. For the accelerometer, previous designs were unable to properly implement the device, which led to some research and the final decision of using an ITG3200/ADXL345 6 DoF accelerometer and gyroscope combination board. This sensor was chosen due to its accuracy, small size (about 20mm by 20mm), and vast libraries and support with Arduino IDE compatibility. This sensor will also be placed within the primary housing of the device amongst the chest region in order to read a child’s movements relative to his or her center of gravity.

For the blood oximeter sensor and pulse sensor, a previous device used, the DD2002/2002M SPO2 pulse oximeter, was decided upon for this project. This device fits the specific measurement requirements for measuring blood oxygen levels and is relatively simple to use, needing to be placed on some thin area of skin such as the earlobes. Given that it was successfully used in previous projects, this sensor was a highly reasonable decision. It should be noted that along with all of the placements of the different sensors and measurement components, hard wiring will be used to connect everything together aside from the Android phone, which will receive all sensor data from the consolidated bluetooth device.

Mimy Ho (Manufacturing Engineer)

Associate task description: A device does not limit a child any physical activity.

Project level 1 requirement #7 describes a child shall maintain full range of motion while wearing a body network. For the finalize product, there shall not be any wire that hang around the device, and all the components (an android phone, electrodes, sensors, accelerometer, and arduino pro) shall be stabilized in the strap.    

Associate task description: Control the android phone and bluetooth radiation

Project level 2 requirement #2 describes Android phone and Bluetooth device will not exceed SAR regulation of 1.6W/kg as stated by the FCC. The SAR value needs to be measured before putting on a child. The SAR value can be obtained by simply dial *#07# on your phone’s dialer.

http://smartntechs.com/technology/a-brief-guide-to-cell-phone-radiationsar-value-and-its-control/

Associate task description: Protect the device if it drops

Project level 2 requirements #4 describes the sensors suit and android phone shall withstand forces of at least 20 Newtons. An android phone and the microcontroller can be protected by an 3D printed case with another silicon protective case wrapped around the corner to avoid any damage in case of a child drops it. The silicon case idea is based on an idea of protecting the damage of a phone when it drops on the ground.

Associate task description: Waterproof electrical components of the device

Project level 2 requirement #5 describes electrical components shall qualify as level two water resistance which is defined as “allows for contact with water such as washing hands or light rain”. Electrical components can be spray with a waterproof coated to prevent events dealing with water.

Associate task description: Meet the deadline

Project level 2 requirement #14 describes In order for project to stay within budget and meet deadline requirements, no purchase may be made for items outside of the United States. The PCB needs to be ordered by the end of March, it takes about 12 days (from A-TeChtoP Friday Spring 2015)

Associate task description: Avoid any burn of a child

Project level 2 requirement #15 describes To avoid harming the child, device will not reach a temperature greater than 113°F. The digital thermometer shall be used to measure the heat absorbed from the boars in the 3D printed case

Associate task description: Avoid any skin reaction of child

Project level 2 requirement #16 describes The wearable device will avoid using materials that can lead to skin irritants caused by an allergic reaction. Since the harness shall be attached directly to the skin, the material of the harness need to documented.

Seizure Watch

Project Level 2 Requirements

System Requirements

Robin Yancey (Systems Engineer)

ELECTRONICS

1.    The sensor shall measure the exosomatic EDA (skin conductance) by injecting a constant current of less than 10 uA/Cm^2 into the two electrodes and measuring the potential difference between the two.

1.1. This is the recommended current limit for these types of devices because it minimizes the risk of damaging the sweat glands [9] [2].

1.1.1.  With the typical range of  skin conductance of about 0.1uS to 15uS, the applied voltage should stay below 10uA×(1/15uS)=0.66V.

2.   Two silver coated disc electrodes (Ag/AgCl) with a contact area of about 1.0 cm^2, shall be used for measurement.

2.1. These electrodes are hypoallergenic, durable, replaceable, and easily snapped onto or off of the wristband [12].

2.2. This is the size and type of electrodes which have been recommended by literature for EDA measurement [3].

2.3. The signals produced with the use of electrically conductive fabrics and interconnects has been shown to be far less correlated with that of FDA approved devices [2].

2.4. Measurements of EDA signals taken using Ag/AgCl electrodes are highly accurate and most widely used because they minimize the development of bias potentials and polarization [16] [15].

3.    The Atmel BTLC1000-MR110CA shall be used for the microprocessor.

3.1. The ATBTLC1000-MR110AC has 2 A/D pins which are required to receive and digitize analog inputs from the EDA sensor [27].

3.2. The module is ultra low-power and comes with built in Bluetooth SMART (BLE 4.1), with and integrated transceiver, modem, MAC, PA, TR Switch and Power Management Unit [27].

3.3. The device has dimensions of 12.7 x 20.152 x 2.0874 mm, which will leave enough room the other sensors, battery, and clock to be held on the face of the device PCB [27].

4.    The microprocessor shall be connected to a 32.768 real time clock, which is able to drive a 6pF load at a desired frequency, and has a maximum signal of 1.2 volts.

4.1. This allows the user to interpret data sample information transmitted via Bluetooth [6].

4.2. In order to comply with BLE specifications the frequency of the clock must be within +/- 500ppm [27].

4.3. the RTC signal must be able to drive the 6 pF internal capacitance of the positive clock input used for a potential oscillator.

5.   A 3-axis accelerometer with a sampling frequency of 32 Hz, 8-bit resolution, and a range of +/-2g shall be implemented to measure acceleration.

5.1. Measurement of the magnitude of body acceleration is necessary to detect and correct external interferences of the EDA signal [20] [12].

4.2. The use of sampling frequencies over 20 Hz or amplitude measurement over +/-2g, has not been shown to give any significant increase in detection accuracy [21].

4.3. Seizure related accelerations can occur in all three dimensions.

4.4. A sampling frequency of 32 Hz is used by commercially sold devices (cited below), such as Empatica E3 [22].

4.5. Use of an accelerometer is a low-cost and accurate method of measuring movement [23].

SIGNAL PROCESSING

6.   The analog signal shall be sampled with a resolution of 11 or 12 bits.

6.1. Within the small range of the conductance (about 0.1uS to 15uS), it should be able to detect amplitude changes at the nano-Siemen level, in order to distinguish between different activities.

6.1.1. For example, using 11 bits we have conductance increments of 14.95uS/(2^11) =7nS.

6.1.2. It would be inefficient to use a higher resolution 12 due to energy constraints.

7.    The EDA sensor value shall be sampled at a rate of 4 Hz.

7.1. The bandwidth of the signal is between about 1 and 2 Hz [14] [11] [13].

a. Using Shannon’s sampling theorem, the sampling frequency must be at least twice the highest frequency in the signal to avoid aliasing. The Nyquist rate is 2*f_max=4 Hz.

7.2. This sampling rate is used by most of the current commercially sold devices for EDA measurement (eg. Empatica, Moodimetric, ect.), as well as current research studies (see all works cited).

8.    EDA signal samples shall be band pass filtered between 0.5 and 2.5 Hz.

8.1. Given that the highest frequencies in the actual EDA signal are about 2 Hz, and frequencies, that do not fall within this range are due to motion artifacts and electrical noise [2] [4] [11].

9.    A machine algorithm shall be designed to detect the rhythmic patterns of a seizure and combine it with the data from the EDA sensor, and automatically send an alert if both indicate a seizure.

9.1. Motion and temperature can easily influence a person’s electrodermal and cardiovascular signals [1] [11].

9.2. Almost all of the EDA devices sold commercially and developed for research purposes have required this to factor out many false alarms that would otherwise occur (see all works cited).

9.2. Although EDA shows increased amplitude for both GTCS and CPS seizures, combined measurement of acceleration and EDA can greatly improve the performance of detection of seizures with motor activity and movement patterns, such as generalized tonic-clonic seizures (GTCS) [22] [23].

10.  The algorithm to detect seizures shall first pre-process intervals of samples for reduction, and then extract significant types of features from the ACM and EDA signals.

10.1. When monitoring throughout the day there is a lot of non-seizure data, pre-processing data will save computational time and workload, since most of the activity caused by the convulsions indicating a seizure occur above 2 Hz [23].

10.2. When the net acceleration of movement of movement is below a certain threshold it can be disregarded as non-seizure movement [23].

10.3. Multiple stages of feature extraction, and comparison with a threshold, will factor out most artifacts and insignificant data, which would cause false alarms [19] [23].

COMMUNICATIONS

11.   Bluetooth IEEE802.15.4 (ZigBee) version 4.0-4.1 physical layer protocol shall be used for communication with the Arduino and the Arxterra control panel.

11.1. This will allow for more than 7 sensor nodes to be connected, at one time [5].

11.2. BLE uses less energy than Bluetooth, so that this device can run without recharge for as long as possible [17].

11.2.1. This is ideal and standard for wearable health care devices because it requires less than 1 mW to communicate to devices up to 30 meters away [5] [17].

11.2.1.1. Compared to classic Bluetooth, BLE uses 0.01-0.5 W and less than 15mA vs. the standard 1 W with less than 30mA [7].

11.2.1.2. The shorter distance range is acceptable for this application.

11.2.2. Compared to classic Bluetooth, BLE takes 3ms to send vs. the standard 100ms.

11.3. The MAC layer protocol implemented system will allow for devices to be moved into or out of the local network of sensors, without an interruption of the communication [5] [7].

11.4. ZigBee protocol was designed with built in security as a top priority, using a master network to keep a list of authenticated devices, who have joined through association, and only responding to those devices [8].

POWER

12.  The wristband shall contain a rechargeable lithium coin cell battery, embedded within the device.

12.1. This is important, so that the child does not have to continuously replace batteries, every time it runs out.

12.2. If it is completely embedded, it will be better protected [10].

12.3. Lithium batteries have a high enough operating voltage, optimal charge-discharge characteristic, are lighter, less rigid, and enclosed in a pouch [18].

12.4. A coin cell battery has enough power to supply the very low voltage requirements of the components, which would allow the device to be both small and light, as required.

13.  The battery shall have enough capacity to support the maximum current drawn from the microcontroller/Bluetooth LE module, and sensor circuit, for at least a few hours, without being recharged to allow enough time for the child to play.

13.1.  When the microprocessor/Bluetooth module is powered by a 3.6 V power source, the module consumes a maximum current of 4.0 mA, and the sensors only draw about 20uA [10].

13.1.1 Back of the envelope calculation: Capacity = Amps×Hours(required), so Capacity= [20uA+4mA+(about 5uA accelerometer)]×(# hours desired by customer)

13.1.1.1. Based on at least 5 research studies cited below, a 3.3-3.7 Volt battery with 1100mAh, will power the device for at least 9 hours (but probably much longer). The above calculation will be used to check the capacity requirement of the battery, once the sensors have been confirmed.

MECHANICS

14.  For ergonomic purposes, the electrodermal activity sensor electrodes shall be placed on the ventral side of the distal forearm, of the non-dominant hand, so that the signal is far less susceptible to motion artifacts.

14.1. Use of this location as a recording site has been shown in numerous studies to be highly correlated to the traditionally used palmar read recordings [2] [3] [4].

14.2. Placement of the device on the the fingers would also impede the user’s fine motor actions [4].

15.  All electronics and wiring shall be concealed and secured within a protective, durable casing, which will not break if the child falls or hits his/her arm on the device.

15.1. Since the child may be playing on a playground structure, it is likely that they will hit their hand on the equipment, fall, or have a seizure related fall, at some point [24].

16.  The face of the device shall not exceed 72g and 54 x 61 x 15 mm (the mass and dimensions of a typical fitness watch) in order for it to be inconspicuous and non-stigmatizing to wear on a daily basis, while not interfering with play activities.

16.1. These are the dimensions and mass of at least one typical fitness watch [26].

17.  The circumference of the wristband shall be adjustable for wrist sizes within +/- 30 mm from 161 mm.

17.1. The average circumference of the wrist of a 13-year-old boy is about 161 mm, while the average for an 8-year-old girl is 138 mm [25].

WORKS CITED:

1. Fletcher, R.R.; Dobson, K.; Goodwin, M.S.; Eydgahi, H.; Wilder-Smith, O.; Fernholz, D.; Kuboyama, Y.; Hedman, E.B.; Ming-Zher Poh; Picard, R.W., “iCalm: Wearable Sensor and Network Architecture for Wirelessly Communicating and Logging Autonomic Activity,” in Information Technology in Biomedicine, IEEE Transactions on , vol.14, no.2, pp.215-223, March 2010
2. Ming-Zher Poh; Swenson, N.C.; Picard, R.W., “A Wearable Sensor for Unobtrusive, Long-Term Assessment of Electrodermal Activity,” in Biomedical Engineering, IEEE Transactions on , vol.57, no.5, pp.1243-1252, May 2010
3. Ming-Zher Poh; Loddenkemper, T.; Swenson, N.C.; Goyal, S.; Madsen, J.R.; Picard, R.W., “Continuous monitoring of electrodermal activity during epileptic seizures using a wearable sensor,” in Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE , vol., no., pp.4415-4418, Aug. 31 2010-Sept. 4 2010
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Subsystem Requirements

Marena William (Manufacturing Engineer)

1. The EDA Watch must consist of a compartment containing the sensors, the Bluetooth module, and a small power supply to provide power to the sensors and the Bluetooth device.
2. The compartment shall be 3D printed from a material that withstand up to 45⁰Celsius (113° Fahrenheit). (See level one requirements)

3. The strap of the watch must be made from a waterproof/semi-waterproof material to tolerate wrist sweat.
4. The strap of the watch must be adjustable to accommodate different hand sizes.
5. The watch must allow a wrist flexibility up to 80⁰ angel, the maximum range the wrist can move according to wikiradiography website. Source: http://www.wikiradiography.net/page/Wrist+Measurements
6. The wristband while be designed to suit for a right-handed or left-handed child and it would be wore on the hand with less activities to allow clear non-noisy measurements and to permit the child to move freely.
7. The housing will be 3D printed from a material that provide protection for the electronics inside.

Design Innovation

(see Creativity Presentation in Central Sensor Suite Design Innovation)

Systems/Subsystem Design

Product Breakdown Structure

Robin Yancey (Systems Engineer)

 

Product Breakdown Structure for Seizure Watch

Electronic System Design

System Block Diagram

Robin Yancey (Systems Engineer)

System Block Diagram for Seizure Watch

Rose Leidenfrost (Electronics Engineer)

System Block Diagram for Seizure Watch

The system block diagram was in part adapted from the previous ATeChToP designs [7]. This updated block diagram describes the interface for the wrist worn seizure detection device. The accelerometer and EDA sensors provide the biological input to the Bluetooth module which is then sent to the android phone via Bluetooth communication. From the android app the information is processed and viewable through Arxterra where parents, nurses or caregivers may monitor the child at play.

Software Block Diagram

Robin Yancey (Systems Engineer)

Software Block Diagram for Seizure Watch

Interface Definitions

Robin Yancey (Systems Engineer)

Interface Definitions for Seizure Watch

Rose Leidenfrost (Electronics Engineer)

Microprocessor/Bluetooth Module: Atmel ATBTLC1000

http://www.atmel.com/Images/Atmel-42514-ATBTLC1000-MR110CA-BLE-Module_Datasheet.pdf

The block diagram of the BTLC 1000 is shown above to display where the different sensors need to be interfaced.

The BTLC 1000 is chosen for its versatility in serving the role of a Bluetooth module and microprocessor. “The module contains all circuitry required including a ceramic high gain antenna, 26MHz crystal and PMU circuitry [5]”.

·         Size – At 2.1 x 2.2 mm, the ATBTLC is the smallest device readily available for this application.

·         Bluetooth – “Atmel’s industry – leading lowest power Bluetooth Low Energy 4.1 compliant SoC” will serve as the Bluetooth interface for the wrist device [5].

·         Features

o   1.62-4.3V input range for I/O

o   2.4GHz transceiver and Modem

o   Single wire antenna connection

·         Applications

o   I2C serial interface with BITalino EDA sensor 151015

o   Analog voltage interface with ADXL335

o   Bluetooth interface with ATeChToP main module

* Suggested by the President, formal trade off studies to follow

EDA sensor: BITalino EDA 151015*

http://bitalino.com/datasheets/EDA_Sensor_Datasheet.pdf

BITalino Electrodermal Activity (EDA) 151015 “translates the changes in the resistance of our skin into numerical values, allowing its use in a wide array of applications [1]”. Using Ag/AgCl electrodes to be placed on the ventral side of the distal forearm [6] as input to the EDA, the variation in resistance of the skin will be accepted and analyzed further for seizure detection.

·         Specifications

o   Voltage: 3.3 V

o   Gain: 2

o   Range: 0-1MOhm

o   Bandwidth: 0-3Hz

o   Consumption: ~2mA

o   Electrodes: 2

Accelerometer sensor: Adafruit ADXL335*

http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL335.pdf

The block diagram above shows the components of the ADXL335 including the 3 axis sensor, corresponding amplifiers and the output with regards to each individual axis. Output will be interfaced with the microprocessor as well.

The Adafruit ADXL335 accelerometer is an industry standard with attractive features suitable for seizure detection as applied to our wrist device. The ADXL335 “can measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion, shock, or vibration [3].”

·         Size – The chip is dimensions 4 mm ×4 mm × 1.45 mm which make it ideal in keeping the wrist device as small as possible.

·         Bandwidth – The accelerometer bandwidth may be adjusted to fulfill the level 2 requirement of 0.5 Hz – 2 Hz.

·         Features

o   1.8V to 3.6V voltage range

o   3-axis sensing ±3 g acceleration range

o   Analog voltage interface

* Formal trade-off studies to follow

References:

[1] BITalino Electrodermal Activity (EDA)

http://www.studica.com/us/en/Bitalino/bitalino-electrodermal-activity-eda/sens_eda1.html?ex_ref=google_feed&gclid=CK7PgbX97coCFQsDaQodzR4Ndw

[2] Electrodermal Activity (EDA) Sensor Data Sheet

http://bitalino.com/datasheets/EDA_Sensor_Datasheet.pdf

[3] Analog Devices, ADXL335

http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL335.pdf

[4] Atmel ATBTLC1000 Xplained Pro USER GUIDE

http://www.atmel.com/Images/Atmel-42538-ATBTLC1000-Xplained-Pro_User%20Guide.pdf

[5] Atmel BTLC1000-MR110CA BLE Module Datasheet

http://www.atmel.com/Images/Atmel-42514-ATBTLC1000-MR110CA-BLE-Module_Datasheet.pdf

[6] Ming-Zer Poh, “Continuous Assessment of Epileptic Seizures with Wrist-worn Biosensors,” Ph.D. dissertation, Dept. Elect. Eng., Massachusetts Institute of Technology, September 2011.

http://affect.media.mit.edu/pdfs/11.Poh-PhD_thesis.pdf

Mechanical Design

Marena William (Manufacturing Engineer)

Watch simple design: Battery wired to the EDA Sensor, the Accelerometer and the BTLC1000. The electrodes coming out of the watch are connected to the EDA Sensor. The output of the EDA Sensor and the Accelerometer are connected to the BTLC1000 chip.

Overall view of the watch and the electrodes to be placed on the palm of the hand.

Design and Unique Task Descriptions

Rose Leidenfrost (Electronics Engineer)

Wrist worn seizure detection

Description: The ATeChToP module will now include a seizure detection device that may be worn on the wrist of the patient.

Task: Construct a watch like housing to encase sensors, Bluetooth module, electrodes, battery and PCB to be worn on the patient’s wrist.

Design: Must be small enough to be comfortably worn by a small child and with minimum weight. This design specification is realized by carefully selecting the smallest components that are commercially available and within budget. Trade off studies for each component will confirm this design.

Task: Wrist device must be able to transmit wireless signals through Bluetooth to the android phone.

Design: The BTLC 1000 module was specifically chosen for its size and application as both a Bluetooth device and a microprocessor to reduce the number of components in the wrist device. Formal trade off study confirming the chip selection to follow.

Task: Wrist device must be capable of detecting whether the patient is experiencing a convulsive seizure.

Design: The combined use of an EDA sensor and accelerometer on a wrist device is capable of convulsive seizure detection [6]. Once a seizure is detected it will be transmitted through the system to produce an alert on the Arxterra panel.

Marena William (Manufacturing Engineer)

Waterproof Options:

1. Most 3D printers use PLA (polylactic acid) or ABS (acrylonitrile butadiene styrene). Waterproofing may be done by adding a silicon layer to the outside of the sensor compartment. [The inside of the compartment wouldn’t be accessible after this]
2. Solution one could be used to waterproof the two separate parts of the design (the bottom&side part and the lid part) then an O-ring along with screws could be used to fasten the two parts together. [Allow access to the inside to replace battery or sensors]