WIRELESS NETWORK OF DISSOLVED OXYGEN (DO)

MONITORS

Sd-May11-20Betty Nguyen

Scott MertzDavid Hansen

Ashley Polkinghorn

AdvisorsJoseph ShinarRuth ShinarwithBob Mayer

Background Existing Solution

Network communication confirmed, prototype

No confirmed DO content measurement

Bulky Code○ No Calibration Messages

Power consumption ~180mA at all times

Non-functional boards○ Faulty boards that would

burn out

Project Objective Implement robust low-power, star topology

network of DO sensors Increase accuracy of DO measurements by

factoring in temperature Implement remote calibration of DO sensors Reduce power consumption of units to increase

battery life of remote sensors Redesign and refactor existing implementation to

increase maintainability and flexibility

Functional Requirements The monitor units shall take readings of dissolved oxygen and of

temperature and use them to calculate DO levels. The monitor units shall wirelessly transmit their readings to the master

controller. The master controller shall request readings from each monitor unit. The master controller’s graphical user interface shall display information

from each monitor unit to the user and allow an operator to obtain data from a specific unit.

The master controller user interface shall allow the user to poll a monitor unit for data.

The Windows service shall log all data processed through the unit in a SQL database.

The network nodes shall create a star-like topology. The Windows service shall send calibration data to each monitor unit. The monitor units shall enter a low-power sleep mode when not in use.

Nonfunctional Requirements The monitor units’ calibration data shall persist across power

loss. The DO monitors and the network coordinator must

communicate when they are up to 1000 meters apart. The system should be able to configure in a star topology. The temperature measurements shall be accurate to ±1

degree Celsius. The DO measurements shall be accurate to ±0.5 ppm. The monitor units’ batteries shall last 14 days.

System Decomposition

DO Sensor Hardware

DO Sensor Theory of Operation

Platinum/Palladium Octaethylporphyrin (Pt/PdOEP) films excited by UV or green OLEDs.

Measure DO by observing the decay constant (tau) of the photoluminescence (PL) of the excited PtOEP films Time (s)

0 100 200 300 400

Inte

nsity

(arb

. uni

ts)

0.0

0.5

1.0

1.5

2.0

Time (s)

10 20 30 40

Inte

nsity

(arb

. uni

ts)

0.00

0.50

1.00

1.50

2.00

100% Ar O2- saturated water

DO Sensor Theory of Operation

1. Excite the PtOEP film

2. Sample PL over time using a photodiode and microprocessor to measure the voltage from the sensor

3. Calculate tau using least-squares exponential fit

1. 0% DO - ~100µs

2. 20% DO (air) - ~30µs

3. 100% - <5µs

4. Calculate DO with temperature (and film) dependent a and b

  

DO Monitor Software

ZigBee NodeNetwork Data Received

Register GUID

Instruction?Yes REGISTER

Get Data Instruction?

No

Calibrate Instruction?

No

PREPARING TO SLEEP

No

GETTING DATAYes

CALIBRATINGYes

CHECKING IN

Has GUID?Max

Register Retries?

No

Yes

SENDING MESSAGE

SLEEPING

WAKING UP

Success? Send to Network ConfirmationNoReached

Max Number of

Retries?

No

Yes

YesNo

Check In or Register

Message?

yes

No

yes

Start MC Time Out Timer

yes

MC Time out

Joined Network

ZigBee Network Coordinator

Is Message Complete?

READY

PACKAGING MESSAGE

SENDING MESSAGE

WRITING TO USART

Joined Network

Success?

More Messages?USART Byte Received

Network Data Received

Yes

Yes

Send to Network Confirmation

Yes

No

Reached Max

Number of Retries?

No

No

Yes

Yes

Master Controller Improvements Modular Message Types Fewer Database Queries Separation of Concerns Calibration Capability Database Relationships

Master Controller Service

ZigBeeMessage

MasterControllerService

CalibrationDataMessage

CheckInMessage

AssignedUniqueIDMessage

RequestUniqueIdMessage

ConfirmationMessageReadingDataMessage

NoActionMesasge

TakeReadingInstructionMessage

CalibrationData

DabatabseAccessor

UartComm

«uses»

«uses»

«uses»

«uses»

«uses»

«uses»

«uses»

Master Controller GUI

MasterControllerGUI

Message DatabaseAccessor

CalibrationDataCalibrationDataDisplay

ReadingData

uses

usesuses

uses

uses

uses

uses

uses

uses

Master Controller Database

DO Sensor Testing Couldn’t compare DO

measurement directly due to old, degradated PtOEP films

Instead, measure tau and compared to lab measurement

100% PL decay too fast to measure with MCU

Temperature measurements within ±1°C

DOLab (us)

Ours (us)

0% 73.8 74.9

20% 35.7 37100% 14.7 13-16

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

f(x) = 90.6668623345085 exp( − 0.0325478503087422 x )

PL decay (PtOEP)Sample Rate = 1.8196us

DO Monitor Unit Power Usage

• Estimated battery life w/out changes (remote, 5 minute period): 2.4 days

• Estimated battery life w/ changes (remote, 5 minute period): 20.2 days

• Estimated battery life w/ changes (remote, 15 minute period): 23.7 days

ZigBee Network Testing Verified ZigBee Node can register with the

Master Controller Verified ZigBee Node can sleep and wake

up Verified ZigBee Node checks in periodically Verified ZigBee Node can wake up the DO

Monitor to get DO Data and for calibration Verified the Network Coordinator can

receive/send messages and interact with the Master Controller

Master Controller Testing

Verified that message are scheduled correctly

Verified that the correct data is displayed Verified that the correct data is exported Verified MC Service’s response to node

check-ins Verified that readings from nodes are

received and stored properly

System Testing Accurate DO and temperature readings

transmitted to the Master Controller and logged Calibration data transmitted to the DO monitor unit Monitors use as little power as possible Calibration and readings are scheduled and

executed on remote devices Readings are retrieved for export and display in

the GUI Network functioned correctly with simulated high

traffic (Increased check-in rate on network of 3 nodes)

What is Next for the Project Integrate Pressure Sensor Handshaking protocol for PC software and

Network Coordinator Switch from Zigbit Amp to Digimesh to

allow for true mesh network with power saving

Reduce current usage to ~5mA in sleep mode

Create Network Coordinator PCB Accurate readings at high DO levels

Conclusions Integrated temperature sensor Brought current consumption down to

~40mA by using a sleep mode procedure Actually measured DO content accurately Upgraded and refined hardware Created a working star network Added calibration utility Documented new and existing code

Questions?