Smart Hiking Bladder. ECE 445 Fall 2016 Final Report. Bobi Shi Shuchen Song Dufei Wu. TA: Kexin Hui

Transcription

1 Smart Hiking Bladder ECE 445 Fall 2016 Final Report Bobi Shi Shuchen Song Dufei Wu TA: Kexin Hui December 4, 2016

2 Abstract The purpose of this project is to make a smart hiking bladder that allows users easily check the water left in the hiking bladder and adjust travel plans accordingly to avoid dehydration. The bladder will keep track of user s water consumption using flow sensors and display on a LCD screen how much water is left. It also includes an android app that can receive data from the device through Bluetooth and help user make better travel plans. After tests and calibrations, we were able to achieve very accurate measurement results for the water consumption. In the end, we will discuss some of the future work of this project. ii

3 Table of Contents 1 Introduction Purpose Features Goals Functions & Features Benefits Summary Design Block Diagram Sensor Unit Water Flow Sensor Hardware Water Flow Sensor Software (correctness compensation) Force Sensitive Resistor Switch Control Unit Microcontroller Bluetooth Power Unit Battery Over-Discharge Protection Voltage Regulator Display Unit App Unit & Bluetooth Communication Design Verification Power System Power Supply Power Consumption Flow Sensors Force Sensitive Resistors Software iii

4 3.4.1 Microcontroller App & App Microcontroller Integration Cost Labor Parts Total Cost Conclusion Accomplishments Uncertainties Ethical Considerations Future Work Appendix A Requirements and Verification Table Appendix B Core Mobile App Code & UI Appendix C Supplemental Figures References iv

5 1 Introduction 1.1 Purpose The water bladder is a necessary and significant hydration component for hiking, camping and cycling fans. However, in most cases, the backpack is full of hiking supplements that are stacked over the water bladder so it is quite annoying for the hiker to take out all the stuff in order to check the amount of water left in the bladder. Due to such inconveniences, the hiker cannot accurately know the amount of water left and might experience unexpected dehydration. Therefore, our project is targeted to solve this problem for the users of water bladder using flow meter, force sensitive resistors, etc. The intelligent water bladder we design could show the water volume left and current water consumption on a LCD screen so the user would be able to know the amount of water he/she still has without taking the bladder out of backpack and then determine whether he/she needs to refill the water bladder. 1.2 Features Goals Enable users to easily determine the amount of water left in the water bladder through a LCD display Help users adjust travel plan with the water consumption rate and the distances travelled Functions & Features Measure water consumption of the user Calibrate the initial water volume Display the amount of water left on a LCD screen Estimate the miles left for the travel plan Communication with a smartphone through Bluetooth Benefits Allow user to make precise travel plan Lower the risk of dehydration during hiking 1.3 Summary We successfully achieved the functionalities of the water bladder for the hiker. Chapter 2 mainly describes our design process, chapter 3 describes our design verification and results, chapter 4 describes the design costs, and chapter 5 describes our accomplishments and future works. 1

6 2 Design 2.1 Block Diagram Figure 1. Block Diagram 2.2 Sensor Unit The sensor unit of our design is composed of two water flow meters, two force sensitive resistors and three switches. We measure the initial amount of water by placing two resistors beneath the bladder. And two flow meters are inserted between the bladder and the straw. From the sensor unit, signals are sent to control unit to communicate with microcontroller for displaying and processing on smartphone Water Flow Sensor Hardware The flow sensor we use can measure water flow accurately in one direction due to the shape of the pinwheel inside the sensor. In our design, the water flows from the bladder to the user when drinking from the bladder. After that it will flow back. In that case, we implemented two flow sensors back to back to measure water flow in both directions as shown in Figure 3. And we call the sensor that measures water backflow the backflow sensor. The flow sensor is also subject to air flow which means it will generate output before the water reaches the sensor. Therefore, the part of the tube between the bladder connection and the flow sensor produces errors and the flow sensor must be placed as close as it can be to the bladder connection. For the backflow sensor, water flow between it and the bladder connection cannot be detected and this distance 2

7 must also be minimized. Those are the reasons we place both sensors close to the bladder connection. Figure 2. Pulses Generated from Flow Sensors Figure 3. Flow Sensor Implementation The signals generated by the flow sensors are 5V peak to peak pulses whose pulse width and frequency depend on the flow rate. In the ideal case, only one flow sensor should generate output at a time allowing us to easily determine the flow direction. We observed ideal results when water flows back to the bladder. However, when water flows to the user, both sensors will generate output as shown in Figure 2. The signals generated from the backflow sensor, although similar in shape, are noises caused by the shaking of the pinwheel under rapid backflow. However, the useful signals from the flow sensors are much denser than the noises, giving us the room to calibrate and determine the actual flow direction Water Flow Sensor Software (correctness compensation) Data measured & Design Procedure The normal way to design a sensor is to use filters. However, as stated above, the flow sensor outputs pulses as signal, and the pulse width is roughly related to the rate of water is flowing through. Using filters may need many circuit translating digital input and the debugging process could be very complicate since we cannot retrieve accurate measurements for the sensor. Nevertheless, the microcontroller gives good mechanism to deal with the pulse-like signals. Also, this concepts of rate measurement make us decide the idea base on PID controller, where the error is calculated based on three terms: proportional, derivative and. Therefore, we tried to use a function to calculate amount of water flowing through for every pulse. Using the P and D term in PID, it should like k " def + k " f(δt), if we define ΔT as the time difference between pulses as in Figure 4. We have also measured raw data as in Figure 4. The chart shows some simple data of the real per pulse water amount, and we have tried to find relationship between averaged water flow amount per pulse and the average ΔT, as plot in Figure 4. The ΔT was averaged from several pulse widths on oscilloscope after measurement. 3

8 Figure 4. Sample Data Collected from Flow Sensor (upper-left), ΔT-water/pulse Plot (right), and ΔT Defination (lower-left) Implementation & Design Detail Here we need to point out that because of the limitation of measuring devices, the data in Figure 4 are only estimations from averages, not accurate. However, we see two important characteristics: 1) The data seems more consistent and having smaller slope when drinking relatively fast (small ΔT); 2) The slope increases greatly when ΔT increases, since the max ΔT we have met was 200ms, whereas the plot shows up to 60ms. Therefore, we have tried functions with more and more curly trajectory, which are showed in Figure 5. First we thought the function should be proportional to flow rate, which is inverse of ΔT. In the Figure 5, function #1&2 are not curly enough and function #3 has an upper limit which does not meet the data we have measured. Then we changed to proportional to ΔT to eliminate the upper limit. Finally function #4: 0.25 tan is used and after verification it achieves the accuracy requirement. 4

9 Figure 5. Formulas Used and Corresponding Plots Force Sensitive Resistor To measure the initial amount of water inside the bladder, we use two force sensitive resisters(fsr) attached to the back of the bladder. A FSR has a round part whose resistance changes with applied force and a long tail for connection to the circuit. One thing we learn through the tests is that it does not respond to uniform pressure. To modify it, we add a small metal ball in the center of the round part, creating a difference of pressure between the center and the edge. After the modification the FSR become really sensitive that even the bending of the tail causes a significant resistance change. In that case, we fixed both sensors on a flat board to minimize all the other factors that may cause resistance change. And the entire sensor module is placed on the back of the bladder. Figure 6. FSR Implementation Figure 7. FSR Schematic The circuit for the measurement uses the voltage divider rule by connecting the FSR with a 47kΩ resistor, as in Equation (1). The voltage across the known resistor is used as the output signal. 5

10 V =7>Ω = 47k FSR + 47k V FF (1) We also use an op-amp as a voltage follower to separate the FSR circuit with the microcontroller to prevent any unwanted feedback from the microcontroller pin. When measuring the initial water volume, the bladder is placed on the table with the sensor part facing down. The change of resistance of the FSR under the pressure of the bladder leads to a voltage change. The microcontroller then display the calculated results based on the voltage output on LCD Switch We use one on/off power switch and two button switches in our design. The power switch is to disconnect the power supply when we tried to turn off the device. The button switches include a reset switch as well as a calibration switch. The reset switch is connected to the microcontroller directly and also to a Bluetooth through a 100µF capacitor. The calibration switch is used by user to set the initial water volume inside the bladder. 2.3 Control Unit The control unit takes signals from the sensors, analyzes the signals and then sends display information to the LCD screen. It also contains a Bluetooth that allows this module to communicate with a smart phone Microcontroller Objective & Design Procedure In our design, we use an ATMega328P to interact with the circuit and hardware. Specifically, when the weight calibration button pressed, the chip will read from the FSR and calculated how many water is in the water bladder. Then, microcontroller will constantly monitor how many water is drunk and reflect it on the LCD. Furthermore, it interacts with the Bluetooth module to communicate with the mobile App to transmit sensor data, and to receive commands. The general question here is how to organize the tasks to achieve desired accuracy and be as energy efficient as possible. The approach usually is putting all things in the loop and checking each one sequentially or using interruption to let the chip only responses when input comes. The final design involves the mixture of these two Design details Since the ATMega328P only have two interruption pins, two flow sensors are connected to them. This is out of two reasons: 1) Accuracy. Some of the operation may take a long time, for example the Serial port interactions. Before those operations finish, some of the pulse may be ignored. Interruption makes sure that every pulse will be detected; 2) Energy efficient. The calculation to compensate the correctness of the flow sensor is relatively expensive and uses a lot of resources. Besides, unlike other sensor, flow sensor needs the loop to run in a very high frequency without sleeping, which will drain more power theoretically. Using interruption can allow the chip to sleep for some time. Other that flow sensor, the digital pins are mainly serving the buttons since they 6

11 only have HIGH or LOW input, and the pins for LCD. Serial port is reserved for the Bluetooth. FSRs are using analog input pins since we need to read voltage level. For details about the program, jobs not related to the flow sensor are run in the loop. Serial input is constantly pulling from the Bluetooth and output is generated when necessary. LCD is also updated constantly about every 1s. In the loop the program will check conditions sequentially and see if need to perform responses to those inputs. These conditions and the work flow are shown in Figure 8, and they are straight forward as in the figure. As mentioned above, only when pulses detected, calculation about flow sensor will be performed. For noises generated from the backflow sensor, we are recording the ΔT of forward-direction flow sensor, only when it bigger than a preset threshold we will calculate backflow, since when water flow back, the forward-direction flow sensor usually does not generate pulses. Figure 8. Flow Chart for Microcontroller Bluetooth Major functionality is same as stated in the section 2.3.1, to make communication possible between microcontroller and the App. We are using the EZ-Link Bluetooth module since its simplicity. After connecting to the serial pins on ATMega328p, using serial communication will make it work. Design choices related to software (e.g. how to receive/send messages) are descripted in section Power Unit The power unit consists of two 3.7V Li-ion batteries, two battery overdischarge protection circuit and a 5V voltage regulation circuit. It provides a voltage of 5V for all the other circuit parts. The input voltage from the 3.7V Li-ion battery is connected to the battery protection circuit so that the output voltage from each battery will be about 0V if the battery discharges to below 2.5V. Then, we connect the output voltage of two battery protection circuits in series to generate 7.4V power source and then connect to the 5V voltage regular to generate 5V power supply. 7

12 2.4.1 Battery The device requires two 3.7V Li-ion batteries in series that gives us 5V - 7.4V input voltage to power the system. At fully charged case, the battery pack provides 7.4V, and as the amount of charges decrease, the voltage drops to 5V in our design Over-Discharge Protection The AP9101C is a protection IC developed for Li-ion battery with a precise voltage detection circuit, as shown in Figure 9. It protects batteries by detecting overcharge voltage, overdischarge voltage, overcharge current, overdischarge current, and turning off the external MOSFET switch. Therefore, we decided to use AP9101C protection IC to prevent overdischarge of the battery. The protection circuit can force the battery to enter a low power mode when the voltage is below the certain voltage cutoff, and this range can be set up by two MOSFETs and is 2.5V. The circuit also allows the battery to resume functioning when it is charged back to above 2.5V. Figure 9. Battery Protection Schematic [8] Voltage Regulator The voltage provided by the battery pack is about 7.4V and we use a linear voltage regulator L4931 to lower the voltage to around 5V which is the working voltage of most parts in our design. The L4931 has very low drop voltage (0.4V) [9] and the very low quiescent current makes it particularly suitable for low noise, low power applications and especially in battery-powered 8

13 system here. The schematic below, shown in Figure 10, shows the voltage output of the regulator when applied input voltage changes. C2 is 0.1 µf input capacitor and C1 is 2.2 µf capacitor. Figure 10. Voltage Regulator Schematic 2.5 Display Unit The display unit is a LCD screen that can display 32 characters in 5*10 dots [3]. It receives digital signals from the microcontroller through 8 digital lines and it can display the current water consumption and the amount of water left in the bladder. Figure 11. LCD Display Schematic 2.6 App Unit & Bluetooth Communication General Design Choices Since the App is running on a completed modern operating system, we utilize many techniques related to multi-threading. We could use very general ideas to let every thread have flags can be changed by other threads and response to those flag values. However, this is over-complicated and not robust. Therefore, we use inter-process communication techniques to solve it. For Bluetooth communication, the socket provided by Android is similar to TCP [1], reliable and ordered, thus only simple messages are needed. 9

14 Design Details Android has provided a great inter-process communication, Handler [2]. One thread can create a Handler and other threads holds a reference of this Handler can send message to the holder thread. The holder will automatically be notified and run a specific code block. Details is shown in Figure 12. First the UI thread will initialize and start other threads. Then when any of those threads has new information received, it will notify the UI thread and reflect the information on UI. When need to send a message through Bluetooth, a new thread of sending message will be created, and end after sending that message. GPS uses the provider provided by the system, and interface from Google Play API. The Bluetooth communication protocol used is very simple, a message is separated by, and each field in a message is separated by :. Each side (microcontroller and App) will parse the received message and perform actions correspondingly. When a message need to be sent, each side will first encode that message and then send. Some basic messages for now are (number is in [] ): W:[weight] for sending new weight info, V:[vol] for sending how many water drunk, R:[0] for recalculating the weight of bladder. Another part of App is UI. Please see Figure 16 in Appendix B as reference. Basically, the first view (left in Figure 16) will let user to choose from a list of devices already paired with phone. After choosing the right device, App will show a dialog box (middle in Figure 16) to show it is connecting and disappear after connected. Finally, a view (right in Figure 16) will show desired information for user in textboxes. Figure 12. Flow Chart for App 10

15 3 Design Verification 3.1 Power System Power Supply The power system includes the IC protection circuit and the voltage regulator circuit. The IC protection circuit will disconnect the battery when the output voltage of the battery is below 2.5V. The voltage regulator circuit should output a voltage of 5V when about 7.4V is given as input Vout (V) Vout vs. Vin Vin (V) Figure 13. Protection Circuit Output vs. Protection Circuit Input In Fig 13. we connect the input of the battery protection circuit to a DC power supply and the output to a multi-meter. Then we start reducing the input voltage from 3.7V (normal battery voltage). As can be seen from Figure 13, when the input voltage is above 2.5V, the output voltage and input voltage are equal. When the input voltage drops below 2.5V, the output will instantly drop to below 0.5V. And when the input is further reduced, the output will be close to 0. This test demonstrates that the IC protection circuit we build disconnect the battery when the voltage is below 2.5 V, therefore protecting the battery from over discharge. 11

16 Figure 14. Voltage Regulator Output vs. Voltage Regulator Input For the voltage regulator, we apply a similar test setup, connecting the input of the regulator to a DC source and output to a multi-meter for a DC sweep. The variation of the output voltage is less than 0.01V (as shown in Figure 14) which could provide a steady power supply for the entire circuit Power Consumption Table 1 Battery Power Battery Number Total Power 3.7V Li-ion battery mAh *2 = 7600mAh Table 2 Total Power Consumption Parts Volta Current( Power Consumption(mW) ge(v) ma) LCD [3] *5=175 FSR [4] *0.1*2=1 Water Flow Sensor [5] *7*1=35 Bluetooth [6] *30=150 Microcontroller [7] *0.2*19=19 Battery Protection IC [8] *0.003*2=0.03 Linear Voltage Regulator [9] *0.01=0.05 Total

17 Total Energy Provided by Battery = 3.7V * 7600mAh = mwh Worst case power consumption = mW Time for Usage = 28120/ = h Maximum Current = 76 ma < Battery Maximum Current =3800 ma 3.2 Flow Sensors For the flow sensor test, we measure around 300mL water using a 100mL graduate cylinder and pour the water into a plastic cup. Then we use the tube (with flow sensors connected to the PCB board) to drink from the cup until there is less than 100mL of water in the cup. After that we measure the water left in cup to get the amount of water that has been consumed during the test. And we compare the data with the results shown on LCD screen. Multiple tests show less than 10mL differences among the results which is less than ±5% variation. The actual accuracy is even higher because some errors can be generated from the test procedures. The graduate cylinder itself has ±1mL error. And pouring water back and forth also generates some errors. 3.3 Force Sensitive Resistors We test the FSR unit by measuring the initial water volume using the PCB starting with 1L water in the bladder. Then we repeat the test by adding 100mL water into the bladder for ten times. The final results for one of the FSRs are shown on the plot. From the data sheet, an exponential relation between the volume and the voltage is expected. However, since the change of resistance for the entire test is small enough, the final results show a very linear relation as shown in Figure 15 which prove to be very convenient. An accuracy of ±10% is achieved in the end. We are unable to achieve a higher accuracy because later we discovered that the amount of air inside the bladder also had an influence on the test results. This effect becomes significant around the 1L region where there is not very much water inside the bladder. To achieve a better accuracy, we propose an alternative suspension system to measure the initial amount which we will discuss in future work section. 13

18 Figure 15. FSR Voltage Output vs. Water Volume 3.4 Software Microcontroller After completing the PCB and connect all of the sensors, we tried to test whether the program responses as expected. We tested after pressing the weight calculation button, whether the weight is measured and displays on the LCD. Also we tested flow sensor as stated in section 3.2 and see if the LCD is displaying the amount of water drunk. Then we have tested the reset button. Finally, we let the program run continually for a relatively long time have performed previous actions several times. In summary, everything worked as expected App & App Microcontroller Integration First we have tested whether the App can connect to microcontroller through Bluetooth, and the connection to GPS. Then, after completing the PCB and connect all of the sensors, we have tested whether the data is synchronized between the App and the microcontroller. Specifically, we tried the same actions as testing the microcontroller and see if the App retrieves those data as well. Also we tried if we can initiate weight calculation from the App. To see if the distance left estimation is reasonable, we observed the estimation under two scenarios: 1) we are moving but not drinking water; 2) we are not moving very fast but drinks a lot. App gives reasonable output for both: 1) can walk more since the average drinking amount is decreasing; 2) can walk less since the average drinking amount is increasing. Also, all of the data synchronization and connections worked as expected since they are retrieving right data and displayed correctly on UI. 14

19 4 Cost 4.1 Labor Total = 2.5* Hourly Rate * Hours in Total Table 3 Labor Cost Name Hourly Rate Hours in Total Total Bobi Shi $ $15000 Dufei Wu $ $15000 Shunchen Song $ $15000 Total $ Parts Table 4 Costs of Parts Item Part Number Unit Cost Quantity Total Cost Water Flow Sensor a ux1194 $ $19.02 Force Sensitive Resistor SEN $ $13.90 LCD HD44780U $ $9.95 Bluetooth 1628 $ $24.95 Microcontroller ATMEGA328P $ $5.95 Water Bladder $ $ V Li-on Battery $ $6.99 Voltage Regulator L $ $1.50 Battery Protection IC AP9101C $ $0.80 Op amp TL074CN $ $0.58 Switch COM $ $1.00 Switch CKN6012-ND $ $ kω resistor CF14JT2K70CT-ND $ $ Ω resistor CF14JT470RCT-ND $ $ kω resistor CF14JT47K0CT-ND $ $ kω resistor CF14JT100RCT-ND $ $ uF capacitor CDV16FF101JO3 $ $ uF capacitor CD15FD221JO3 $ $ pF capacitor 229CKS6R3M $ $ pF capacitor CD5EC220JO3F $ $2.24 MOSFET FQP30N06L $ $3.80 Total $

20 4.3 Total Cost Table 5 Total Costs Section Total Labor $45000 Parts $86.18 Total $ Conclusion 5.1 Accomplishments We are able to achieve all the functionality requirements for this design. The data extracted from sensors are accurate enough for the microcontroller to calibrate initial water volume and keep track of the water consumption. Bluetooth can make connection with cellphones and the android app provides reasonable estimation of the remaining distance to travel. The battery can also supply power for more than 70 hours according to our calculation. However, the FSR sensor unit can be improved to achieve a higher accuracy. 5.2 Uncertainties When measuring the initial amount of water in the bladder, the amount of air inside the bladder has an effect on the pressure over the FSR. Also, the bladder must be placed on a flat surface to achieve accurate results. These parts can be improved by several ways which we will include in future work. In rare cases, the software in the microcontroller will be terminated for no reasons, causing failure of the circuit. It could be caused by the interrupt of noises which result from imperfect circuit connection on PCB. Further tests are needed to solve this problem. 5.3 Ethical Considerations Our project presented in this document will be implemented and strictly followed the guide of the IEEE code of ethics [10]. 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; Since we are designing the hiking bladder, the safety and health issue is the primary consideration for customers. Firstly, the water quality should not be deteriorated after the water flow sensor added on the tube since it is the only component that directly contacts flowing water. Secondly, the 9V alkaline battery might be another safety concern because the overheat might cause the explode releasing harmful chemicals and breaking the bladder. Certain battery protection is required. 16

21 2. to avoid real or perceived conflicts of interest whenever possible, and to disclose them to affected parties when they do exist; Since this is a course related project and we are not planning to make it into the market, the conflicts of interest with other existences is unlikely. 3. to be honest and realistic in stating claims or estimates based on available data; to reject bribery in all its forms; We claim to be honest on using any data retrieved from our real testing and use them as the base of our conclusions. And we will not involve in any forms of bribery even this is project is only academic purpose. 4. to improve the understanding of technology; its appropriate application, and potential consequences; Our smart hiking bladder benefits hikers in the way of easily telling them the water left in their bladder through the LCD display without taking the physical bladder out of backpack. Also, dehydration problem of hiker can also be solved. 5. to maintain and improve our technical competence and to undertake technological tasks for others only if qualified by training or experience, or after full disclosure of pertinent limitations; Our team members are qualified on high level skills of design either forcing on the hardware complexity or concentrating on the software applications. 6. to seek, accept, and offer honest criticism of technical work, to acknowledge and correct errors, and to credit properly the contributions of others; All the suggestions from professors and TAs will be took account for completing our design. Any technological supports, knowledge supplements and resource will be properly credited. 7. to treat fairly all persons and to not engage in acts of discrimination based on race, religion, gender, disability, age, national origin, sexual orientation, gender identity, or gender expression; All team members have proper and equal manner and attitudes toward all people we meet. 8. to avoid injuring others, their property, reputation, or employment by false or malicious action; All team members will strictly follow the lab safety guideline avoiding any inadvertently caused damages on equipment and other people. 9. to assist colleagues and co-workers in their professional development and to support them in following this code of ethics. All team members are willing to help others who need further assistants from us and this ethical analysis will help them in following IEEE code of ethics. 17

22 5.4 Future Work To improve this design in the future, first we would like to make waterproof package and coating for the PCB circuit. Our design will constantly make contact with water. Although the circuit part is always separate from the water and we have implemented protection circuits for the power system, waterproof circuit part is necessary to ensure the lifespan of the design. The size of the PCB needs to be reduced. Currently our PCB is designed to be relatively large in size for soldering and testing convenience. A more compact circuit will reduce the size and weight of the entire design and is preferred to reduce the load for hikers. As an alternative way to calibrate initial water amount, a suspension system is preferred because it does not require a flat surface to do the measurement. During our design process, we tried stretch sensors and load cells. The stretch sensor is unable to stabilize and the signals from the load cell is too small to provide any useful output. However, given enough time we believe we can find a way to make a handle using a load cell with the right measurement range to meet the accuracy requirements for the measurement. 18

23 Appendix A Requirements and Verification Table Table 6 Requirement and Verification Requirement Verification Points 1. Flow Meter a. Provide quantity of liquid flowing with the accuracy of ±10% (flow sensor itself has ±5% error) b. Verify communication between Flow meter and the Microcontroller c. The output voltage for bit 1 of the flow meter will be above 4.5 V when the input voltage is 5 V ± 0.5 V d. The output voltage for bit 0 of the flow meter will be less than 0.5 when the input voltage is 5 V ± 0.5 V 1) Verification procedure for requirement a a) Apply 5V voltage to the sensor b) Use a graduate cylinder to measure 300mL of water c) Pour the water into the beaker d) Use the straw and drink from the beaker until there is less than 100mL water left e) Measures the water left to get the water consumption f) Check if the results calculated are consistent with the amount of water in the beaker with the accuracy of ±10% g) Repeat test five times and take average 2) Verification procedure for requirement b a) Connect the output pin of the water flow meter to the microcontroller as well as the oscilloscope b) Drink from the bladder c) Extract the data from the microcontroller and compare the results 3) Verification procedure for requirement c & d a) Apply 5V to the flow sensor a) ±10% b) Y c) Y d) Y 19

24 b) Connect the output of the flow sensor to the microcontroller c) Use an oscilloscope to measure the voltage of the output d) Drink from the bladder for 1 seconds and check the data from the oscilloscope to verify the requirement 2. Force-Sensing Resistor a. Provide weight of liquid with the accuracy of ±10% in the range of 1L to 2L of water 1) Verification procedure for requirement a a) Set up the sensors as described and put bladder on flat table b) Apply 5V voltage to the sensor c) Use a beaker to measure 1L of water and pour all the water into the bladder d) Record to calculate the estimated amount of water (the actual relationship between the volume and V will be determined during tests in set up) e) Verify if the two results are consistent with accuracy of ±10% f) Without pouring out the water, add 100 ml more water into the bladder and repeat the test g) Repeat the step g for ten times a) ±10% 3. Power System 1) Verification procedure for requirement a and b a) Connect 5V power source to 20kΩ resistor. a) Y b) Y c) Y 20

25 a. Provide 5 V ± 0.5 V and 0.3mA for active mode for microcontroller b. Provide 5 V ± 0.5 V and maximum 0.3mA for the low power operation of LCD c. Provide 5 V ± 0.5 V and maximum 0.1mA for round forcesensitive resistor d. Provide 5 V ± 0.5 V and maximum 10mA current for water flow counter sensor e. Provide 5 V ± 0.5 V and maximum 40 ma to Bluetooth f. Battery Protection circuit will disconnect the circuit when the battery voltage is below 2.5V or above 4.4V b) Use multimeter in parallel with the resistor to measure the voltage difference across it. c) Verify the voltage across between 4.5 V to 5.5 V. 2) Verification procedure for requirement c a) Connect 5V power source to 10kΩ resistor. b) Use multimeter in parallel with the resistor to measure the voltage difference across it. c) Verify the voltage across between 4.5 V to 5.5 V. 3) Verification procedure for requirement d a) Connect 5V power source to 1kΩ resistor. b) Use the multimeter in parallel with the resistor to measure the voltage difference across it. c) Verify the voltage across between 4.5 V to 5.5 V. d) Y e) Y f) Y 4) Verification procedure for requirement e a) Connect 5V power source to 1kΩ resistor. b) Use multimeter in parallel with the resistor to measure the voltage difference across it. c) Verify the voltage across between 4.5 V to 5.5 V. 21

26 4. Microcontroller a. Certain code can run on an interruption based situation b. It can receive the digital 0 and 1s from external devices 5) Verification procedure for requirement f a) Connect the function generator to the input of the protection circuit and set a DC voltage of 2.4V and 4.5V b) Check the output of the circuit to be disconnected and verify the results 1) Verification procedure for requirement a a) Connect the corresponding interrupt pin to an external signal generator b) Attach the interrupt service routine to the corresponding pin in the software. The routine should have some clear indications of the its running. c) Start generating the signals and observe the indications 2) Verification procedure for requirement b a) Connect the corresponding input pin to an external signal generator b) Write programs which will have different indications when receive 0 or 1 at the corresponding pin c) Start generating the signal, and observe the indications. Also the voltage might need to be changed to see the threshold between 0 and 1. a) Y b) Y 5. Smartphone app 1) Verification procedure for requirement a a) Open our own app a) Y b) Y 22

27 a. Interface to display the movement based on data from GPS b. Base on the data transmitted from Bluetooth, App gives reasonable estimations and notification. 6. LCD Display a. Display the amount of water left in the bladder b) Move with the phone to let the GPS unit give reasonable detectable position changes c) Check that the interface reflects the change of the position 2) Verification procedure for requirement b a) Set up the app and take over its input by some preset data, which will represent the walking distances and remaining water level b) See from the interface of the app to verify it gives reasonable estimations and notification according those data 1) Verification procedure for requirement a a) Set up the microcontroller for displaying b) Print out the information through microcontroller c) Transmit data to LCD display from microcontroller d) Compare and verify the accuracy a) Y 7. Bladder a. No leakage from the water meter connection. 1) Verification procedure for requirement a a) Fill out the bladder with 2L of water and seal b) check whether there is leakage from the flow meter connection using a dry tissue a) Y b) Y 23

28 b. User should be able to sip water from the bladder with flow meter is set up. c) Apply pressure to the bladder by put a 2kg object on top of the bladder d) Check again if there is any leakage 2) Verification procedure for requirement b a) Fill the bladder with 2L of water b) Drink water from the straw of bladder with flow meter running c) Feel the difficulty of the sipping d) Check if it is possible to drink most of the water from the straw 24

29 Appendix B Core Mobile App Code & UI Figure 16. User Interface 25

30 Main Handler in UI Thread: 26

31 Class for Bluetooth Initialization: Function for Decoding Bluetooth Messages: 27

32 Thread for Receiving Bluetooth Messages and Handler sendto() Example: 28

33 Appendix C Supplemental Figures Figure 17. Schematic of Overall System 29

34 Figure 18. PCB 30

35 References [1] Google, "BluetoothSocket," [Online]. Available: [2] Google, "Communicating with the UI Thread," [Online]. Available: [3] HITACHI, " [Online]. Available: [Accessed 2 December 2016]. [4] I. Electronics, " [Online]. Available: [Accessed 2 December 2016]. [5] " Uxcell, 17 July [Online]. Available: [Accessed 2 December 2016]. [6] "Bluefruit EZ-Link - Bluetooth Serial Link & Arduino Programmer," adafruit, [Online]. Available: [Accessed 2 December 2016]. [7] Atmel, "ATMEL 8-BIT MICROCONTROLLER WITH 4/8/16/32KBYTES," [Online]. Available: ATmega48A-48PA-88A-88PA-168A-168PA P_datasheet_Complete.pdf. [Accessed 2 December 2016]. [8] Diodes, "Single Cell Solution For 1-Cell Li+Battery Pack," May [Online]. Available: [Accessed 2 December 2016]. [9] "Very low drop voltage regulators with inhibit," October [Online]. Available: [Accessed 2 December 2016]. 31

36 [10] IEEE, "IEEE Code of Ethics," [Online]. Available: [Accessed 2 December 2016]. 32