Humidity , Humidity Sensor, Circuit of Humidity Sensor and block diagram of the Humidity Circuit

Humidity Definition

§  Humidity   is  a  term  used  to  describe  the  presence  of  moisture  or  water  vapor  in  the  air .  The  amount   of  moisture  that  the  air  will  hold  depends  upon  the  temperature  of  the  air .  Warm  air  will  hold  more  moisture  than  cold   air.  Dry  air  causes  rapid  evaporation  .  Moist  ( humid )  air  prevents  rapid  evaporation  making  it  feel  warmer  than  the  temperature  indicated  by  thermometer .

§  Relative  humidity   is   defined  as  the  actual  vapor  pressure  on  the  value  that  would  occur in  the  space  was  occupied  by  steam  in  saturation  conditions  and  expressed  in %

                          

§  Absolute humidity  is the weight of water vapor in a given volume of atmosphere (air) and is expressed in kg of water vapor per cubic of dry air .

Effect  Of Humidity On The Greenhouse Climate

Humidity is one of the environmental factors that must be in proper balance for satisfactory greenhouse cultivation .

Plants have to  transpirate water to transport nutrients , to cool and to regulate growth . 

The transpiration depends on the saturation deficit between the Stomata’s and the air .

Problem  definition:

The following can be said :

 *Too high and low saturation deficits have unfavourable influence on plant ; physiology and growth :

•         When air humidity is too high ,the gas exchanges are restrained causing low transpiration of the plant and therefore low nutrient absorption.
•        When air humidity is too low ,the stomates close, reducing photosynthesis rate .

*  High humidity  can also induce difficulties in pollination because wet pollen cannot be released .

             *  The humidity of the air in the plant favours diseases.

Solving of the problem:

By designing greenhouse control system we can control some parameters which have agreat effect on plants grow and one of  the most effective factors on plants is humidity.

Controlling of humidity can be realized by using humidity sensor which provides accurate measures of relative humidity according to this measures we can control the humidity and generating the right action that leads to maxmimum product of plant.

humidity sensor that we used in our system is 

 HS1101Relative Humidity Sensor

Why  HS1101 Relative Humidity Sensor?

Features 

                         

Ø Simple calibration required when operating in standard conditions.

Ø Fast response time.

Ø Simple, RCTIME output corresponds to  relative humidity when directly connected to BASIC Stamp.

Ø Compatible with automatized assembly  processes , including wave soldering , reflow and water immersion.

Ø Suitable for linear voltage or frequency output circuitry.

Ø High reliability and long term stability.

 Circuit & equation:

Connecting and Testing

Connecting the HS1101 to a microcontroller is demonstrated here with a BASIC Stamp module. It is a straightforward application, requiring only one I/O pin.

 Since the HS 1101 is based on a unique capacitive cell, relative humidity can be obtained using a simple RC wiring diagram, 

TDecay = 2.4 %RH + Rhconstant

Key Specifications

Ø Power requirements: 5 to 10 VDC.

Ø Communication: Analog output of varying capacitance in response to change in relative humidity.

Ø Humidity Measuring Range:

       1 to 99% RH

Ø Operating temperature: -40 to 212 °F (-40 to 100 °C)

Application Ideas

Ø Home and office automation

Ø Humidity component for weather station applications

Ø Industrial process control systems

 The block diagram of the humidity circuit is as the following:

Read more »

Light, Light Sensor , Circuit of Light Sensor and Algorithm of Light circuit

The light sensor is a unique tool that can come in handy for numerous uses such as measuring objects and detecting objects. The tool is used in labs for scientists, in offices for the general work force and in home security systems.

Definition

A light sensor is a mechanical device sensitive to light, temperature, radiation level, that transmits a signal to a measuring or control instrument, according to Dictionary.reference.com. 

Similar to how the human eye is sensitive to light and body hair is sensitive to nearby objects, the light sensor is a tool that is sensitive.

Function

This instrument can be used to give information on distance, shape, speed, dimensions and types of substances contained in various objects, depending on the area of study it is being used for. 

With a high level of precision, they are used for measuring purposes in architecture and offset printing. (A type of printing process used by large commercial printers. The ink doesn't press directly on the paper, it is distributed from a metal plate to a rubber mat where it then proceeds to the paper.

Proplem Definition

Nobody doubts the important role played by light on crops. The greenhouse must collect a maximum of sum radiation all day long in winter, and every morning  and every evening all the year round to get a favourable thermal balance from short IR and allow active photosynthesis through the “visible” (provided no factor involved in the process falls down to the minimum, i.e. is missing to a certain extent .

The intensity or the level of light, has a vital effect in the velocity of  the photosynthesis  process which is essential to all green plant , the duration of light, or day length, also has profound photoperiodic influence; and sources of artificial light, as distinct from sunlight, have different simulative effects on plants.

Types of artificial lighting are; Tungsten filament, Discharge lamps, and Fluorescent lamps.

The Effective reflection ensures that the maximum amount of light is concentrated on mum amount of light is concentrated on the plants being treated.

The main roles for lighting in greenhouse are:

1-To allow working on short winter days or in the evening.

2-To provide day-length manipulation or night-break techniques by the use of low intensity tungsten filament lights, suspended above the plants.

3-To supplement the natural daylight when if falls below at level sufficient to maintain optimum photosynthetic activity, and to improve vegetative development and flower truss initiation a high intensity light .

4-To illuminate growing rooms.

How we solve the problem?

We control the light of greenhouse using PIC microcontroller and light sensor LDR which sense the intensity of light in the greenhouse and if the light is not enough an external lamp switched on compensating the low light .

Light Dependent

Light-dependent sensors are inexpensive and commonly used for gauging and responding to light levels. These light sensors work as automatic switches for different devices. They belong to a group called photoresistors because their resistance increases as light levels increase, which is why they're commonly present in outdoor lights like streetlamps. As light levels increase, their resistance increases and turns the lights off or down.

we will use LDRLight Dependant Resistor in our system control.

Why LDR?

·        Automatic Headlight Dimmer

·        Night Light Control

·        Street Light Control

·        Position Sensor

·        The relation between LUX and resistance is linear as shown in figure

Algorithm:

1-set the setting point of the light intensity of greenhouse according to the type of plant on the greenhouse.

2-The sensor contimously sensing the light intensity in the greenhouse  as variation in its resistor.

3-The sensor enter its analog signal to A/D converter.

4-The A/D converts the analog signal into digital signal giving it to the controller.

5- The controller compare the signal coming from the sensor with  the setting point :

-If the light intensity coming from the sensor is less    than the setting point   then

Lamp is turned on .

-else

The lamp still off.

How do you connect LDR sensors with a PIC ??

It will not work with just the LDR. You need to measure voltage at one of the ADC inputs. The voltage comes from a potential divider made from a fixed resistor and the LDR in series with the ADC connected to the center. If you omit the fixed resistor the LDR will pull the PIC input high, even under dark conditions and the ADC will always read maximum voltage.

Note that there are two ways you can connect this: 
1. LDR goes to the supply, resistor goes to ground.
2. Resistor goes to supply, LDR goes to ground.

Option 1 will give an increasing voltage as it gets brighter but you have to carry the supply line wherever the LDR is mounted. If it shorts to anything you could damage the supply or the wiring.

Option 2 will give a decreasing voltage as it gets lighter but this is easy to compensate in software. It has the advantage that the LDR is grounded at one end and the resistor limits the current, giving some degree of protection.

The optimum resistor value will give best voltage swing between lightest and darkest conditions. Typically, choose a value equal to the mid way between LDR dark and LDR light resistances.

There are just two ways of constructing the voltage divider, with the LDR at the top, or with the LDR at the bottom:

You are going to investigate the behavior of these two circuits. You will also find out how to choose a sensible value for the fixed resistor in a voltage divider circuit.

Remember the formula for calculating V_out :

 The block diagram of the light circuit is as the following

Read more »

Temperature, Temperature Sensor , Circuit of Temperature Sensor and Algorithm of temperature circuit

• Temperature

Temperature Definition:

• Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot.
  Quantitatively, temperature is measured with thermometers, which may be calibrated to a variety of temperature scales.
• temperature is different from heat, though the two concepts are linked. Temperature is a measure of the internal energy of the system, while heat is a measure of how energy is transferred from one system (or body) to another. The greater the heat absorbed by a material, the more rapidly the atoms within the material begin to move, and thus the greater the rise in temperature.

Effect of temperature on plants

Temperature has a great effect on plants, as very hot and very cold weather can prevent a plant from setting blooms, and it can even cause the plant to start  dropping foliage.

Plants produce maximum growth when exposed to a day temperature that is about 10 to 15°F higher than the night temperature. This allows the plant to photosynthesize (build up) and respire (break down) during an optimum daytime temperature, and to curtail the rate of respiration during a cooler night.

High temperatures cause increased respiration, sometimes above the rate of photosynthesis. This means that the products of photosynthesis are being used more rapidly than they are being produced. For growth to occur, photosynthesis must be greater than respiration.

Low temperatures can result in poor growth. Photosynthesis is slowed down at low temperatures. Since photosynthesis is slowed, growth is slowed, and this results in lower yields.

Problem  definition:

The main problem is how to provide  suitable  temperature for plants growing as there is climatic changes every time which affects on plants in passive manner.

Then the question which arises now how to  control the temperature?

Solving of the problem:

By designing greenhouse control system we can control some parameters which have agreat effect on plants grow and one of  the most effective factors on plants is temperature.

Controlling of temperature can be realized by using temperature sensor which provides accurate measures of temperature degree and according to this measures we can control the temperature and generating the right action that leads to maxmimum product of plant.

Types of tempreture sensors:

When selecting which type of sensor to use there a myriad of considerations that must be made depending specifically on the application.

 Additionally however when selecting a sensor it is important to consider the temperature range, the required accuracy and response time as these will vary with different measuring methods.

When accuracy is of prime importance an RTD sensor is preferable although for those with an eye on finances, thermocouples are clearly the cheaper, more affordable option. Hopefully the following break down of the RTD, thermocouple and infrared thermometer will help operatives make the decision.

The temperature sensor that we used in our system is LM35 General Description

The LM35 series are precision integrated-circuit temperature

sensors, whose output voltage is linearly proportional to the

Celsius (Centigrade) temperature.

The LM35 thus has an advantage

ü over linear temperature sensors calibrated in° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling.

ü The LM35 does not require any external calibration or trimming to provide typical accuracies of ±1⁄4°C at room temperature and ±3⁄4°C over a full −55 to +150°C temperature range.

ü Low cost is assured by trimming and calibration at the wafer level.

ü The LM35’s low output impedance,linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy.

ü It can be used with single power supplies, or with plus and minus supplies.

ü As it draws only 60 μA from its supply, it hasvery low self-heating, less than 0.1°C in still air.

The LM35 is rated to operate over a −55° to +150°C temperature range,while the LM35C is rated for a −40° to +110°C range (−10°with improved accuracy).

The LM35 comes in many different packages, including the following.

·         TO-92 plastic transistor-like package,

·         T0-46 metal can transistor-like package

·         8-lead surface mount SO-8 small outline package

·         TO-202 package. (Shown in the picture above)

Why  lm35?

Features

ü Calibrated directly in ° Celsius (Centigrade)

ü Linear + 10.0 mV/°C scale factor

ü 0.5°C accuracy guaranteeable (at +25°C)

ü Rated for full −55° to +150°C range

ü Suitable for remote applications

ü Low cost due to wafer-level trimming

ü Operates from 4 to 30 volts

ü Less than 60 μA current drain

ü Low self-heating, 0.08°C in still air

ü Nonlinearity only ±1⁄4°C typical

ü Low for 1 mA loadimpedance output, 0.1

What Does An LM35 Look Like?

Circuit & equation:

·         How Do You Use An LM35?  (Electrical Connections)

o    Here is a commonly used circuit.  For connections refer to the picture above.

o    In this circuit, parameter values commonly used are:

§  V_c = 4 to 30v

§  5v or 12 v are typical values used.

§  R_a = V_c /10^-6

§  Actually, it can range from 80 KW to 600 KW , but most just use 80 KW.

o    Here is a photo of the LM 35 wired on a circuit board.

§  The white wire in the photo goes to the power supply.

§  Both the resistor and the black wire go to ground.

§  The output voltage is measured from the middle pin to ground.

The general equation used to convert output voltage to temperature is:

§  Temperature ( ^oC) = Vout * (100 ^oC/V)

§  So if  Vout  is  1V , then, Temperature = 100 ^oC

• The output voltage varies linearly with temperature

The Algorithm of temperature circuit:

·        The user enter the set point through the computer.

·        The temperature sensor comparing the temperature that it measures with the set point and performing an action which is turning heater or fan according to some condition.

·        If (set point +5) < temperature sensor then turn on fan with high speed.

·        Else If temperature sensor >set point & temperature sensor < (set point +5) then turn on fan with low speed.

·        Else If set point > temperature sensor & temperature sensor > ts1(set point - 5)  then turn on one led

·        Else If ts1(set point - 5)  > temperature sensor & temperature sensor >ts2(set point - 10)  then turn on two leds

·        Else turn on the three leds

·        End if.

The block diagram of the temperature circuit is as the following:

Read more »