cape buoy

Members: John DeBlanc Elias Ellsworth Peter Bankole Luis Chinchilla

Mentors:

Nick PughMark Fenstermaker

Satellite Communications BuoySenior Design II

Fall 2008

Outline

•Introduction

•Purpose

•Functional Specifications

•High Level Block Diagram

•Introduction to Buoy System Model

•Satellite Access Scheme

•Data Budget

•Sensor Subsystem

•Link Budget

•Communications Subsystem

•Power Budget

•Power Subsystem

•Onboard Computer

•Mechanical Subsystem

•Summary

•Acknowledgments

Introduction

•This design project will develop a satellite communications buoy.

•This buoy will communicate with a Low Earth Orbiting (LEO) CubeSat; namely, the C.A.P.E. II

•This project will combine the desirable features of satellite communications and low power requirements for future buoys and other remote applications.

Purpose

•Gather environmental data and then upload it to the C.A.P.E. II.

•Demonstrate the usefulness of CubeSats in the area of data collection and forwarding.

•Create a new arena for opportunities and applications within the CubeSat community.

•Open doors for future University of Louisiana at Lafayette senior design teams that could develop other terrestrial applications with satellite link functionality.

Functional Specifications

BuoyBuoy

Compatible Compatible

w/ Naval Academy Buoyw/ Naval Academy Buoy

On-board GPS ReceiverOn-board GPS Receiver

Memory > 100 MegabitsMemory > 100 Megabits

Data Interface (I2C)Data Interface (I2C)

Low Cost Low Cost

4) Sunlight

1) Environmental Data

2) Location

3) Time

5) Satellite Commands

Inputs

1) 145MHz and/or 435MHz Transmission Frequency

2) Sufficient Transmission Power To CloseLink With CAPE2

3) Transmit Location, Time, and Environmental Data

Outputs

Power SystemSolar/Batteries

Environment

Large Body Of WaterPotentially Harsh Weather

High Level Block Diagram

Sensors

GPS

PIC

External

Memory

Solar Cells Batteries

Power System

TNC Radio

TX TX

RX RX

Mechanical

PVC Structure

Buoy System Model

Data Budget

How much data is collected?

Comm. Budget

How much signal is needed?

Power Budget

How much poweris required?

SatelliteSatellite

Satellite Access Scheme

Beacon Buoy

“Aloha?”

Beacon "aloha" every 4 minutes.

If acknowledged by satellite,

upload weather data.

Wait 24 hours until next

satellite contact attempt.

• The buoy will measure 8 environmental variables plus GPS location and time

• If the buoy measures these variables 24 times a day, we collect about 1.4kilobytes

Data Budget

• Anemometer

• Compass

• Water Temp

• Humidity

Sensors

• Wind Vane

• Air Temp

• Pressure

• Salinity

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• The wind speed would be detected using 3 cups anemometer assembly and a 0H090U Hall Effect Transistor

• The 3 cups anemometer assembly as a magnet in its center. The magnets would be used to detect the rotations of the cups.

Calculation v(m/s) = 2*pi*f ( r ) r = radius from center of shaft to center of cups. r = 0.053mm v = velocity in meters/sec

Anemometer

•The wind vane includes a 5k Dual Wiper Potentiometer which uses a 540 degree format and analog input range – 0 to 5V

• It would also include a tail and a pointer that would point in the direction of the wind. The Tail and the pointer will help rotate the potentiometer to the direction of the wind.

• A 3 Axis digital Compass (TTL) is used to orient the wind direction to its true north

Wind Vane

• Features: - Azimuth - Inclination (Pitch and Roll)

- 3 Axis magnetic sensors from Honeywell

- 3 Axis Accelerometers(G) from ST Microelectronics

- 24 bit differential Analog to Digital Converter from Analog Devices

- Four sentence formats for data parsing

- Tera Terminal software for COM

- Multiple baud rate(4800, 9600, 14400, 192000, 38400, 57600, 115200)

- Built in Temperature Sensor (-40C to 85C) for compass board

(0S500-T) 3 Axis Compass (TTL)

• A DS1621 DIP Temperature Sensor

is used to determine the air temperature sensor. It ranges from -55C to 125C and it uses I2C communication bus to communicate with a data handling system

• The DS1621 is placed inside a non- conducting epoxy for the water temperature Sensor

Air / Water Temperature Sensor

• The humidity of the air would be detected using dry and wet bulb thermometers

• The humidity is calculated based on a comparison between the wet bulb temperature and the dry bulb temperature. This method is used for some psychrometers.

Humidity Sensor

•The MPX4115AP Pressure Sensor would be used to measure air pressure. It ranges from 15 to 115kpa

• A 0.17 ID, 0.25 OD POLYETH TUBE would used as an atmospheric vent

Pressure Sensor

•Requires two electrodes mounted inside PVC

• Uses IRF7831 MOSFET Switch to turn on sensors

• MAX4372 Op. Amplifier for voltage

• Output: 0 to 5v range for ADC conversion

• The salinity would be determined by finding a relationship between the voltages and salinity through a graph. A mathematical formula would be derived from the graph because the voltages are proportional to the salinity

Salinity Sensor

Link Budget

Communications – Link Testing

¼ Wave Antenna – 6W TX Power

Naval Academy LEO PCSAT

Antenna Polarization

Low power 3V Radio

Handheld Radio

Picopacket TNC-X

Communications - Radio

Power Budget

•How did we go about designing the Power Subsystem?

Total System Power Units Amount

Total Onboard Computer Power PER DAY Watt-hours 0.3685176

Total Communication Power PER DAY Watt-hours 3.7863978

Total GPS Power PER DAY Watt-Hours 0.48

Total Sensor Power PER DAY Watt-Hours 0.1277

General System Power PER DAY Watt-hours 4.7626154

Power – Power Subsystem

•Batteries vs. Solar Panels + Batteries:

•Batteries have a limited lifetime.

•Solar panels will provide a longer lifetime to batteries to satisfy the buoy’s power needs.

•Sealed Lead Acid Battery

•Poor weight-to-energy density

•Inexpensive

•Low-self discharge

•Multiple Solar Panels

•Collect as much sunlight as possible

Power – Experiments

•Peak Power Point

•Use solar panels efficiently

•Different Peak Power Points

•Generic vs. Atlantic

•Which one is better?

Generic Atlantic

Power – Experiments

Generic Atlantic

Typical Voltage Volts 14.75

Typical Current Amps 0.09499

Typical Power Watts 1.40110

Time In Sun Per Day Hours 3.3

Power Per Day / Panel 1 (Direct Sunlight) AH 0.313467

Power Per Day / Panel 1 (Direct Sunlight) WH 4.62363825

Indirect Sunlight Percentage % 20.00%

Power Per Day / Panel 2 (Indirect Sunlight) AH 0.0626934

Power Per Day / Panel 2 (Indirect Sunlight) WH 0.92472765







Total Power Generated Per Day (Amp-hours) AH 0.362054385

Total Power Generated Per Day (Watt-hours) WH 5.340302179

Typical Voltage Volts 12.65

Typical Current Amps 0.06235

Typical Power Watts 0.78873

Time In Sun Per Day Hours 3.3

Power Per Day / Panel 1 (Direct Sunlight) AH 0.205755

Power Per Day / Panel 1 (Direct Sunlight) WH 2.60280075










Total Power Generated Per Day (Amp-hours) AH 0.237647025

Total Power Generated Per Day (Watt-hours) WH 3.006234866

Power – Regulating Power

Step-down voltage : 12 V to 5 VLinear Regulator vs. Switching Regulators:

-Linear:- Take the difference between input and output voltages.

-Difference voltage is converted into thermal energy Wasted as heat-Efficiencies: 14% to 40%

-Switching:-Takes small amounts of energy from input voltage and moves it to output.

-Relatively small energy loss.-Efficiencies: 70% to 85%

-Conclusion:-Switching Regulator Efficiency > Linear Regulator Efficiency.

Power – System Features

-Controlled Solar Charging

-Prevent solar panels from overcharging batteries

-Using a MOSFET as a switch between solar panels and batteries

-Microcontroller will open / close switch depending on battery charge

-Control Other Subsystem’s Power

- Some components will not be used all the time.

- Use of MOSFETs as switches to selectively power buoy components

-Watchdog Timer

-Resets the Microcontroller

-Momentarily cuts the power to the Microcontroller and Subsystems

-Reset a latch up condition

DG

Solar Panel

S

Battery

Power – Final Calculations

Total System Power Units Amount

General System Power PER DAY Watt-hours 4.7626154

Solar Power Harnessed PER DAY Watt-hours 5.340302179

Surplus Power From Sun Watt-hours 0.577686779

•Despite conservative assumptions about sunshine per day and

system inefficiencies this power system design exceeds the buoy's

power requirements.

Onboard Computer

Coordinating the Subsystems

Sensors

Power

Comm

Satellite CommunicationsWeather Buoy

The Buoy State Machine

WaitShort

GetData

Aloha

DataTx

WaitLong

Finished TX

Data Gathering State

Fetch current data from the environmental sensors and GPS

- struct ENVIRONS* GetEnvirons();Pressure(kPa), Humidity(%), Air Temperature(degrees),

Water Temperature(degrees), Salinity(mg/L), Wind Speed(mph), and Wind Direction(N,S,W,E,NE,NW,SE,SW)

-struct GPS* GetGPS();Time, Longitude, and Latitude

Store Data On I2C EEPROM

Aloha State

Attempt to contact satellite

Acknowledged Not Acknowledged

WaitShortData

TxAcknowledged

Data Tx State

Upload environmental data to satellite

[Buoy Address],[Date],[Time],[Latitude],[Longitude],A[Air Temperature],W[Water Temperature],H[Humidity],WS[Wind Speed],WD[Wind Direction],S[Salinity]

03,101809,053021.32,2501.23.N,9002.18.W,A088,W084,H060,WS015,WDNW,S32

WaitLong

Finished TX

Wait Short State

Waiting between data gathering and alohas

60 Minutes 4 Minutes

Aloha4 Minutes PassedGetData

60 Minutes Passed

Wait Long State

Waiting while accumulating a 24 hour data set

60 Minutes

GetData

60 Minutes Passed WaitShort

24 Hours Passed

24 Hours

Power Management State

Disable Solar Charging

EnableSolar Charging

Low Power Mode

Cease ActivityUntil Voltage >= 12.4

100% Charge 80% Charge 30% Charge

Regulate System Voltage

Mechanical - Construction

Bending PVC for Solar Panel MountsFinal Result

Mechanical

Antenna

Solar Panels

3 ft Discus

Aluminum Struts

Payload

Mechanical - Stability Test

Insert VideoHere

Sensors Physical Mount

Summary

FuncSpecs

FunctionalBlock

Diagram

SatAccessScheme

BuoySystemModel

+ -DesignChoices

DataBudget

LinkBudget

PowerBudget

Onboard Computer

CommSubsystem

PowerSubsystem

SensorsSubsystem

Mechanical

Acknowledgements

•Special Thanks to:

•Nick Pugh

•Mark Fenstermaker

•Fenstermaker and Associates

•Dr. Zhongqi Pan

Questions?

Appendix

•Satellite Data Transmission

•Salinity Testing Schematic

•Power Subsystem Schematic

•Sensors Subsystem Schematic

•Main Board Schematic

•Angle of Incidence

•Buoy System Model Spreadsheet

•Communication Subsystem Schematic

•TNC - X Schematic

cape buoy

Technology

buoy system model data

total gps power

air temperature sensor

kilobytes data budget

total communication

salinity salinity sensor

low power requirements

data handling system