1

Weather Station Project

TemperatureLight Dark Sensor

Wind SpeedWind Direction

2

Light/Dark Sensor Construction

Circuit Connection

• The circuit is built based on LDR (photo resistor) an operational amplifier 741

• The LDR is used as a light sensor which resistance change with intensity of Light

• Op Amp 741 amplifies voltages going out from LDR to reach the PLC specification 0-10V

0.36-1.3 V 0-1900 Counts

3

Light/Dark Sensor Objectives

Characteristic of LDR Main Objectives of the device• The LDR Characteristic

shows decrease resistance compare to increase light intensity (LUX)

• Ideally the sensor should detect even small changes in light intensity and convert them to relative voltage between 0-10V

4

Light/Dark Sensor ResultsTest type Vout [V]

Light ON 1.3

Light ON 1.35

Light OFF 11.22

Light OFF 11.3

Shadow 5-7

Test type Units

Resistance Day Light 0.18kΩ

Resistance Darkness 2.93kΩ

Resistance Light Source in Distance 10mm 0.02kΩ

LDR Voltage Day Light 0.36V

LDR Voltage Darkness 1.3V

Test type Volts Range [V] (depends on variable resistor resistance)

Day Light 0.08-10.53

Darkness 0.8-9.83

Device Results Op Amp Input

LDR Measurements

5

Light/Dark Sensor Conclusions

Final Conclusions and changes• The main goal was achieved. The device works and detect light

changes. Sensitivity regulation is possible by changes in potentiometer's resistance, however the resolution stays on the low level. It means that the sensor works in mode on/off and doesn’t detect small changes in the light intensity.

• The supply voltage was decreased from 12V to 9V to provide suitable power source from two batteries 4.5V connected in series.

• By changes in power supply the “Dark Voltage” drops from 11.22V below 10V and can be detect by PLC.

• Despite the device doesn’t work as was assumed at the beginning of the project it’s still can be used in the project as Light/dark sensor or cloud detector.

6

Wind Direction Sensor Design

• For this instrument we decided to show wind direction in its 8 most uses directions, N, NE, E, SE, S, SW, W, NW. The design of the instrument is quite simple, each directional point has its own resistive circuit which all connect to a common single resistor across which the voltage is measured to give us our direction. It is essentially a voltage divider circuit.

• We divided our 10V supply voltage by 8 (No. Of directions) and chose resistor values for each directional circuit in order to scale our voltage output evenly across 8 steps (as can be seen in the table below).

Direction Contacts

ADMODULE

PLC

WINDVANE

PYTHON

MySQL

APACHEWEBSERVER

INTERNETEXPLORER

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Wind Direction Sensor Design

• The device is fed by a 10V DC supply through the directional arrow’s shaft and on to the direction contacts sticking up from its box, and according to what direction the wind is blowing a different voltage output is generated.

• The directional arrow can only be in contact with one circuit at a time so as not to give a false reading. It is based on the more complicated vane that measures wind direction in 360 degree format. With the addition of more directional circuits our model could measure wind direction in the same manner, in theory.

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Wind Direction Sensor Results

DIRECTION RESISTANCEOHMS

CALCULATEDVOLTAGE

MEASUREDVOLTAGE

NW 7K 1.25V 1.25V

W 3K 2.5V 2.5V

SW 2K 3.3V 3.3V

S 1K 5.0V 4.99V

SE 500 6.6V 6.58V

E 300 7.69V 7.68V

NE 200 8.33V 8.32V

N 0 10V 10V

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Wind Direction Sensor Conclusions

We are quite pleased with how well this instrument turned out, it is durable and its success lies in its simplicity. Because we

used a 0-10v DC supply to begin with we could

connect the vane directly to our PLC which was

helpful and because there is a substantial difference

between each of our 8 input voltages it is unlikely that an error could occur

in the PLC.

Temperature Variable Assembly

LM 324N: Used to amplify voltage using negative feedback

Resistor values• Ri=474 Ω• Rf=10 kΩ

Gain ( ) = 22.09

With these resistor values, we got a gain of 22.09, which enabled us to get a good voltage swing (0-10 volts) from our LM35 temperature sensor.

Vout

Vin

Rf

Ri

= 1+

Vout

Vin

Soldered cables with heat

shrink

LM35 temperature

sensor

LM 324N Instrumentatio

n amplifier

Amplified Voltage Temperature oC

0.03 0

0.1 1

0.3 2

0.64 3

0.72 4

1.02 5

1.36 6

1.63 8

2.36 10

2.6 11

4.12 18

5.08 23

7.76 35

Complete Assembly

Temperature v Amplified Voltage

0 1 2 3 4 5 6 7 8 90

5

10

15

20

25

30

35

40

Temperature v Amplified Voltage

TemperatureLinear Trendline

Amplified Voltage

Tem

pera

ture

oC

Block Diagram & Conclusions

Conclusions• Max. operating temperature from LM35 = 100 C • Min. operating temperature from LM35 = 0 C

– Unsuitable for detecting negative temperatures

• Amplified output voltage is linearly proportional to the temperature (C)• Low power consumption• Good output voltage swing from amplifier for A/D conversion in the PLC

9V Battery

LM324N amplifier

PLC A/D card

(12 bit)

PC SCADA System

LM35(0-35 C)

0-0.35 V 0-7.76 V 0-1900 counts Website DisplayHTML

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