Critical Design Review24 February 2004

Weather Bulletin Board System (WeBBS):

Fahid Jahrami, Arian Lalezari,Justin Lasiewicz,

Joshua Miers, Nathan Seidle

Overview

• Approach– Block Diagrams– Division of Labor

• Specifications– Power– Wind Sensor– Microcontroller– Misc. Sensors– Communication– Enclosure/User Interface

• Schedule– Milestone I/II, Expo

Block Diagram:Power Assembly

Sealed Solar Panel8.5V 250mA in direct

sunlight

TPS621023.6V DC-DC Buck

Iq = 250µA

TPS621025V DC-DC Buck

Iq = 250µA

6.7V LM317Constant voltage charging of Lead Acid Chemistry

6V, 5Ah BatterySealed Lead Acid

1A Automotive FuseProtects against melt-down

Block Diagram:Sensor Platform

DS18S20.5º C Precision TemperatureI2C interface

PIC 16F877A Flash memory based C

unit with boot loader

MPX4115A Motorola Barometric

Pressure - Analog Output

HS1101Relative HumidityVariable Capacitor

24LC25632kB I2C EEPROM

3 Days of 5-Min Readings

Cell Phone Data CableUART control over

incoming and outgoing data

Serial LCDIn-House 16x2 design

2.5V Precision Reference

±0.2% 2.5V ReferenceDetects absolute power levels

Wind SensorSolid State Ultrasonic

PWM Output

Power ConsumptionMonitors current usage

throughout system

Power ControlPowers down circuit

elements when not in use?

5V 50mA Burst

3.6V 400mA Burst

Division of Labor

• Power:– Fahid and Josh

• Communication and Enclosure:– WeBBS

• Wind Sensor:– Justin

• Microcontroller and misc. sensors:– Nate

• User Interface and Documentation:– Arian

Specifications:Power Distribution and

Regulation• Power Regulators– PQ20RX05 (Iq =

4mA)

– TPS62102? (Iq = 250A)

• Power Requirements– Sensors & C: 4.4mA– Cell Phone: 8mA– Wind Sensor: 500A– Regulators: 2× 4mA

– Total: 20.9mA

Specifications:Solar Cell

• Solar World part number SPE-225-6– 8.5VOC

– 250mASC

– 2W

– 41/2” x 61/4 ”

Specifications:Battery

• Part Number BP4-6-T1– Sealed Lead-Acid– 6V, 5Ah

• Discharge Test– 6V 4Ah (backup)

battery– 8.2 load (I =

732mA)– 5.46hr expected life

Specifications:Battery

• Anticipated Usage– Iavg =

20.9mA

– tchg = 4.5hr

– Calls: 4 × 2min

Specifications:Charging Circuit

1. Solar cell input, Vin

2. On/off switch3. Vout. Note diode to prevent back flow from the battery, etc.

4. Set-voltage for the regulator to charge at 6.3 Volts5. Ground

Specifications:Wind Sensor

•Parts–EFR-TSB40K5–EFR-RSB40K5

•Note–40kHz is within hearing range of some animals–Two 12.5s chirps every 5 minutes

Specifications:Wind Sensor

Specifications:Wind Sensor

•Prototype Test–40kHz square wave Vin

–Falling-edge triggered

•Test Results–Noticeable change when blown on

Specifications:Microcontroller

• Parts– 16F877A

• Software– Wake/Sleep on

Command

• Interface– RS232 Data

connection for programming and data acquisition

Specifications:Miscellaneous Sensors

•Parts–Temperature (I2C)

–Dallas DS18B20

–Baro. Pressure (ADC)

–Motorola MPX4115AP

–Humidity ( = RC)–Humirel HS 1100

–Precipitation (TTL)–Pending Confirmation

Specifications:Communication

•Parts–Samsung A310, LG VX10, Sprint TP1100–Embedded Socket Modem–Serial data cables

•Interface–AT command set–Used as modem at 14.4kbps–Power Interface Pending

Specifications:Enclosure

• Custom Plexiglas enclosure– Weatherproof– Transparent (for Expo)– Opaque (for installation)

• Dimensions (Projected)– 10”×10” surface– 5” height– Slanted 41/2” x 61/4 ” solar cell mount

Implementation:User Interface – Preliminary

• Data dump to Windows Application– Excel– Visual Basic

• Data dump to HyperTerminal– Test Scheme Prepared

• No on-station displays– Concern: Power

Implementation:User Interface – Projected

• Automatically updating web application

• On-station displays– LCD on box

(backlight?)

Schedule

Milestone I:16 March 2004

• Power– Long-term field tests

of charge and discharge with solar cell

• Wind Sensor– Calibration and

enclosure finalized

• Microcontroller– Calibration of

functional software implemented

• Miscellaneous Sensors– Calibration and testing

finalized

• Communication– Prepare link to C,

home base for testing– Finalize modem tests

• Enclosure/UI– Begin preliminary

enclosure– Finalize ghost and tests

with simulated input

Milestone II:6 April 2004

• Power– Finalize tests, design– Begin final installation

• Wind Sensor– Finalized, calibrated,

and installation begun

• Microcontroller– Testing of software

completed– Installation begun

• Miscellaneous Sensors– Enclosure

specifications finalized

• Communication– Tests and enclosure

specifications finalized

• Enclosure/UI– Begin final enclosure

construction– Test with field-

generated input

Questions

??