COMM-Research Project

Design of a Network of Low Cost Weather Stations

Presentation by Group 1

Start

An Overview of The System

Application Processor

Measurement of Physical Phenomena

Statistical Analysis and Data Representation

Transmission

Home

St. Augustine South, Tunapuna-Piarco

26 March, 3:47 pm

25º

THIS WEEK

0º

Monday

EM

9º

Pressure

Tuesday

UV

Max Temp.

Rain

6.8

kPa

25º

29.7

15º

Wednesday

Humidity

Wind Speed

20º

Thursday

70%

18

Km/h

25º

Friday

Soil Moisture

By month

Min Temp.

Soil Temp

25º

Wind Direction

Saturday

Jan

12º

25%

27°

NE

0º

Sunday

Thermistor-Based Temperature Sensor

A thermistor is a resistive element, of which the resistance has a large variation with the temperature that the element is placed in. This sensor works by exploiting this property!

A constant, known current is run through the thermistor. By making use of Ohm's Law,

the resistance of the thermistor, R can be found by measuring the voltage accross the element. The temperature of the environment in which the element has been placed can therefore be determined by simply matching the calculated resistance to the corresponding temperature value.

Capacitive Humidity Sensor

1. This sensor consists of two oscillators - one which produces a reference waveform, and the other produces a measured waveform. The output of the measured waveform is fed into a capacitor that is exposed to the environment.

Reference Waveform

Output Waveform

2 . Humidity is the measure of the water content in the atmosphere. The permittivity of the dielectric material within the capacitor, ε will vary as it absorbs moisture from the atmosphere, thus varying the capacitance of the capacitor. The capacitive humidity sensor exploits this property of the dielectric material.

Filtering

Measured Waveform

3. As the humidity of the environment changes, the moisture absorbed by the dielectric material changes. Therefore the capacitance of the capacitor changes. The change in capacitance causes the amplitude and phase of the measured oscillator signal to change.

4. The resultant signal is filtered to produce a DC voltage, whose value is dependent upon the capacitance of the capacitor, and thus the humidity of the environment.

Piezo-Resistive Pressure Sensor

1. Barometric Pressure is the force exerted by air molecules per unit area, at a point within the Earth’s Atmosphere.

P1

2. This sensor makes use of a piezo-resistive cantilever as the pressure sensing element. A piezo-resistive material has the property whereby its electrical resistance varies as it is mechanically deformed.

P2

3. The piezoresistive cantilever is placed at the opening of a cavity. When there is a change in the pressure difference between the interior and exterior of the cavity, a force is exerted on the cantilever, causing it to bend downwards. This changes its electrical resistance.

P1 > P2

4. The change in electrical resistance causes a corresponding change in the current through the element, which is converted to a voltage signal.

Tipping Bucket Rain Guage

1. A rain gauge is an instrument that measures the intensity of rainfall, in millimeters per unit time.

2. This system uses specifically a Tipping Bucket Rain Gauge.

Funnel

3. Rainwater enters the instrument through the funnel and falls onto a vessel that is mounted on a pivot point. The weight of the rain water throws the vessel off balance, causing it to tip to one side. The tipping of the vessel results in a magnet coming into close proximity with a reed switch, triggering it. The reed switch causes the generation of a pulse when triggered.

Vessel (Tipping Bucket)

Magnet

Reed Switch

4. The amount of water that causes the vessel to tip can be varied. Rainfall intensity can therefore be found from the amount of generated pulses that occured in a specified time.

Wind Vane

1. A wind vane is an instrument that determines the cardinal direction and compass heading that the wind is blowing from. It does this by using a surface with a large area, to catch the wind and thus turn a pointer into the direction of the wind.

2. To quantify the direction the direction that the pointer has been moved, the design consists of 8 light dependent resistors (LDRs) - resistive elements whose resistance varies according to light intensity. Each LDR corresponds to a cardinal direction

3. When the pointer turns in a particular direction, an opaque surface blocks the LDR below the pointer from light produced by an LED on the pointer.

4. The resistance of the LDR increases due to being blocked from the light, causing the output of the circuit to go low. Thus, the cardinal direction in which the wind is blowing from can be determined from the particular LDR circuit whose output is at a LOGIC Lo.

Cup Anemometer

1. An anemometer is an instrument that measures wind speed.

2. In this design 3 cups, each displaced from each other by 120o were mounted onto a shaft to catch the wind. As the wind blows, the cups and the shaft rotate.

3. The rate of this rotation is proportional to the wind speed! It is therefore desirable to measure the rate of rotation of the shaft.

4. This was accomplished using a shaft encoder - a disc that is mechanically encoded with a pattern that can be used to determine its rate of rotation.

5. The figure to the left shows a bottom-up view of the sensor, so that you can see the shaft encoder in action! As the wind blows, a force is exerted on the cups which causes the shaft and therefore the disc of the encoder to rotate.

6. As the disc rotates, a photo-sensitive element, which has an infra-red LED directed towards it, generates a pulse train whose frequency is proportional to the wind speed!

Wind

Thermopile Pyranometer

1. A thermopile pyranometer is an instrument that accurately measures solar irradiance in W/m2 by using the thermoelectric effect.

2. Solar irradiation is the quantity that measures the energy per unit area of incident of solar radiation on a surface measured in W/m2.

3. The central element to this instrument is the thermopile. The thermopile is a stack of two different conducting materials. It generates a voltage in response to the temperature difference between the hot and cold side of the stack. The hot side is the black absorbing surface and the cold side is a part of the sensor body.

4. The output signal is an analog DC voltage that is proportional to the solar irradiance.

Crookes Radiometer

1. A Crookes Radiometer is an instrument that is used to measure electromagnetic radiation by converting light radiation into rotary motion.

2. It consists of a glass bulb containing a partial vacuum with a set of vanes that are mounted on a rotor inside it.

3. Each vane is polished on one side and blackened on the other and they are arranged such that the polished side faces the black side. When light strikes the white side, the radiation is reflected but when it hits the black side, the radiation is absorbed. This causes the air particles near the blackened side to be hotter and this exerts a greater pressure on the black side causing it to rotate.

4. The rate of rotation depends on light intensity. The output signal from radiometer is converted into a DC analog voltage by using a frequency to voltage converter.

Integrated-circuit Temperature Sensor

1. The LM35DZ sensor is an integrated circuit temperature sensor that can used to measure soil temperature.

2. Its analog output voltage has a linear relationship with Celsius temperature.

3. The soil temperature can be calculated using the formula:

where T = Soil temperature, °C Vout = Soil temperature output voltage, mV Kt = the linear scale factor (10.0mV/°C)

Frequency-domain reflectometry sensor (FDR)

1. An FDR is a sensor that is used to indirectly measure the volumetric water content based on the dielectric properties of the soil medium.

2. It consists of a sensing component that is placed in the soil and an oscillating circuit. The operating frequency depends on soil dielctric constant.

3. This method determines the dielectric constant of the medium by measuring the charge time of a capacitor which uses that medium as a dielectric.

4. The soil serves as the dielectric in the capacitance sensors, which are made up of a pair of electrodes (either parallel spikes or circular metal rings). Changes in the operating frequency are used to detect variations in soil moisture content as the oscillator and capacitor form a tuned circuit.

GPS Module

1. Global Positioning System (GPS) is a satellite-based navigation system which provides geographical location-based information to a GPS receiver anywhere on Earth.

2. There are multiple satellites that orbit the earth and constantly send signals to GPS receivers. GPS receivers receive the information from these satellites and determine your position through a process based on the intersection of spheres known as trilateration.

3. If a GPS receiver can see at least four satellites, it can accurately calculate your geographical position as well as time.

4. The output signal of the GPS module is an analog DC voltage.

Neo 7M GPS Module

Real Time Clock (RTC)

1. Real-time Clock (RTC) is a digital clock usually in the form of an integrated circuit that is responsible for keeping track of date and time .

2. The main advantage of a RTC is its ability to operate even when the power supply is turned off or the device is placed in low-power mode. It is commonly used in personal computers, (PC), embedded system and servers.

3. RTCs regulate its clock by counting the number of cycles of an oscillator usually a 32.768Hz oscillator quartz crystal.

Arduino interfaced with DS3231 RTC Module

4. The output signal of a real-time clock is a digital signal.

Where the Magic Happens - The Microcontroller

Pins

Peripherals

Core/CPU

Where the Magic Happens - The Microcontroller

Wait! Don't press the red button yet! To understand what the core of a microcontroller is, one must first understand the concept of the sequential and combinational logic circuit.

• A combinational logic circuit is a system whereby the output is dependent on the present input only! An example of this is a simple OR gate, where the output depends only the the present value of its two (or more) inputs.

• The output of a sequential logic circuit however depends on the present input and the past outputs via the use of memory elements and a periodic clock signal

• Consider the diagram on the right. In this case, the combinational circuit is an AND gate with a past output of 1 and a present input of 1. But what happens when we apply a next cycle of the clock signal?

Output

Input

1 1 1 0

Combinational

Memory

CLock it!

Clock it

Where the Magic Happens - The Microcontroller

What happened here?

• When the memory element saw the next rising edge of the clock, it assigned its input, which was dependent on a past input to the system, to the input of the combinational circuit! This caused the output to change its state to 0.

• The core of a microcontroller is essentially a large sequencial circuit, consisting of many smaller sequential circuits like the one depicted in the diagram on the right!

• The simple operation we just saw is basis of operation of a microcontroller core, which is responsible for excecuting all programs - mathematical calculations, logical operations and coordinating all activities within the microcontroller!

1 0 0 1

Output

Input

Combinational

Memory

CLock it!

What aspect of transmission would you like to explore?

TCP/IP PROTOCOL STACK

COMMUNICATIONTYPES

COMMUNICATION PROTOCOLS

THE TRANSMISSION PROCESS

The Transmission Process

step 1

step 2

step 1

step 3

step 4

The Wi-Fi transciever would convert the data into a signal to be transmitted.

The data recieved at the station is then sent to the webserver via the internet

The signal is then boosted and transmitted via a directional antenna

The transmitted signal is then received at a base station

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+info

+more

+more

+more

+more

Communication Types

Wired Communication

Wireless Communication

Coaxial Wires

Wi-Fi

04

Satellite

Fiber Optics

Communication Protocols

Inter System

Intra System

UART Protocol

I2C Protocol

SPI Protocol

USART Protocol

USB Protocol

CAN Protocol

TCP/IP Protocol Stack

What is the best way to send data over the internet?

IP

TCP Protocol

Internet Protocol

Transfer Control Protocol

The IP is responsible for addressing the data packets to ensure that they are sent to the correct destination. This is called the IP address and it is checked whenever data needs to be sent to a computer on the network

. The TCP controls how the data is transmitted by controlling how the communication channels are created and how data is assembled before transmission and reassembled at the receiver.

How would we analyze all this data?

With this huge influx of data from the sensors, there is a specific term used for processing this amount of data...

Big Data Analysis!

Big Data Analysis

Big Data Analysis is the process of using various techniques and algorithms to determine trends, insights, and patterns in large datasets.

There are different algorithms that can be used for big data analysis. Some of these algorithms are:

• Linear Regression
• Logistic Regression
• Classification and Regression Trees
• K Nearest Neighbour
• K-Means Clustering

Click on the eye for a link to see software used for Big Data Analytics

Diagram of Weather System