Research & Development Electronics Electrical

Appropriate environmental conditions are necessary for optimum plant growth, improved
crop yields, and efficient use of water and other resources. Automating the data acquisition
process of the soil conditions and various climatic parameters that govern plant growth allows
information to be collected at high frequency with less labor requirements. The existing systems
employ PC or SMS-based systems for keeping the user continuously informed of the conditions
inside the greenhouse; but are unaffordable, bulky, difficult to maintain and less accepted by the
technologically unskilled workers.

The objective of this project is to design a simple, easy to install, microcontroller-based
circuit to monitor and record the values of temperature, humidity, soil moisture and sunlight of
the natural environment that are continuously modified and controlled in order optimize them to
achieve maximum plant growth and yield. The controller used is a low power, cost efficient chip
manufactured by ATMEL having 8K bytes of on-chip flash memory. It communicates with the
various sensor modules in real-time in order to control the light, aeration and drainage process
efficiently inside a greenhouse by actuating a cooler, fogger, dripper and lights respectively
according to the necessary condition of the crops. An integrated Liquid crystal display (LCD) is
also used for real time display of data acquired from the various sensors and the status of the
various devices. Also, the use of easily available components reduces the manufacturing and
maintenance costs. The design is quite flexible as the software can be changed any time. It can
thus be tailor-made to the specific requirements of the user.

This makes the proposed system to be an economical, portable and a low maintenance
solution for greenhouse applications, especially in rural areas and for small scale agriculturists.

CIRCUIT WORKING:

OUR complete  project is to be divided into  6 sections.

Power supply.

Sensor signal conditioning

Analogue to digital converter.

Microcontroller interface.

LCD  connectivity.

Output interface.

POWER SUPPLY

5 VOLT REGULATED POWER SUPPLY CIRCUIT.

In this project firstly we use one step down transformer. Step down transformer step down the voltage from 220 volt Ac to  12 volt Ac. This Ac voltage is further converted into DC with the help of rectifier circuit. In rectifier circuit we use four diode. All the diodes  are arranges as a bridge rectifier circuit. Output of this rectifier is pulsating Dc. To convert this pulsating DC into smooth dc we use one capacitor as a filter components. Capacitor converts the pulsating Dc into smooth DC with the help of its charging and discharging effect.

Output of the rectifier is now regulated with the help of  IC regulator circuit. In this project we use positive voltage regulator circuit. Here we use three pin regulator. Output of this regulator is regulated voltage. If we use 7805 regulator then its means its is 5 volt regulator and if we use 7808 regulator then its means that it is 8 volt regulator circuit. In this project we use 5 volt dc regulated power supply for the complete circuit.

SENSOR’S:

TEMPERATURE SENSOR

In this project we use many sensor’s . Out of these sensor’s one sensor is temperature sensor. Here in this project we use LM 35 as a temperature sensors. LM35 is very accurate and very good sensor to show the temperature in celicus. For body temperature measurement we use IC LM34 sensor. LM35 is a linear temperature sensor. To convert this output for the input of the ADC we use op-amp  current amplifier to convert the signal into 0-5volt dc.Here in this project we use  op-amp op07 ( industrial amplifier ).LM 35 is connected to the pin no 3 of the op-amp via 2.2k ohm resistor. Pin no 2 which is –ve input of the op-amp is set to the reference voltage by 1k variable resistor. Centre point of 1 k ohm resistor is connected to the pin no 2 via 10 k ohm resistor. Positive voltage is also applied to the one shaft of the preset via 3.3k ohm resistor. 4.7k ohm resistor is also grounded from the 1k variable resistor. Pin no 7 of the ic is connected to the positive  5 volt . Pin no 4 is connected to the common ground point. One feedback resistor is connected from output pin to the pin no 2 which is 50 k ohm resistor. So by this way we set the gain of 5 by this opamp. We set the minimum reference voltage by preset ( variable resistor) and when temperature rises then output is also increases with the gain of 5 and connected to the  IN0 input of the ADC.

Temperature Sensor – The LM35

The LM35 is an integrated circuit sensor that can be used to measure temperature with an electrical output proportional to the temperature (in ^oC)

The LM35 – An Integrated Circuit Temperature Sensor

• Why Use LM35s To Measure Temperature?
  • You can measure temperature more accurately than a using a thermistor.
  • The sensor circuitry is sealed and not subject to oxidation, etc.
  • The LM35 generates a higher output voltage than thermocouples and may not require that the output voltage be amplified.

• What Does An LM35 Look Like?
• What Does an LM35 Do?  How does it work?

• It has an output voltage that is proportional to the Celsius temperature.
• The scale factor is .01V/^oC
• The LM35 does not require any external calibration or trimming and maintains an accuracy of  +/-0.4 ^oC at room temperature and +/- 0.8 ^oC over a range of 0 ^oC to +100 ^oC.
• Another important characteristic of the LM35DZ is that it draws only 60 micro amps from its supply and possesses a low self-heating capability. The sensor self-heating causes less than 0.1 ^oC temperature rise in still air.

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)

• How Do You Use An LM35?  (Electrical Connections)
  • Here is a commonly used circuit.  For connections refer to the picture above.
  • 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.

• 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.l

Here we use lm 35 is connected to the op-amp circuit to amplify the current Output of the LM35 is further connected to the pin no 26 of the ADC. Here we use 0809 Adc to convert analogue signal into digital signal. This signal is further connected to the microcontroller.

 SOIL MOISTURE SENSOR.

In the soil moisture sensor we check conductivity of the soil . for this purpose we insert two probes in the field. If the field is wet then conductivity is more and resistance is less. If the field is dry then conductivity is less and  resistance is high. To measure the conductivity we use one NPN transistor  circuit. Emitter of the NPN transistor is connected to the input of adc and collector of the transistor is connected to the positive supply 5volt. Base is biased through positive voltage through 100 ohm resistor in series with the conductivity probe. Emitter voltage is also set by the one variable resistor 10 k. One point of the 10 k ohm resistor is connected to the positive point and  third point of the 10 k ohm resistor is grounded. Centre point of the 10 k ohm resistor is connected to the emitter of the transistor and go though the  input of ADC IN2. As the base voltage is change according the  resistance of the field. ADc input is also change .

LIGHT SENSOR:

In the light sensor we use one LDR. LDR is a light dependent resistor. Resistance of the ldr is depend on the intensisty of the light. As the light on the ldr is change , resistance of ldr is also change. Resistance of the ldr is varies from 1k ohm to 500 k ohm. In full llight resistance of the ldr is very low   below then 1 k ohm and in no light resistance of the ldr is become very high above then 500k ohm.

In this project we use ldr with only one 10k ohm variable resistor. This 10 k ohm resistor is connected to the positive voltage 5volt.

ADVANTAGES

Low cost

Reliable

Portable

Flexible  due to microcntroller

Easy to use- system is very easy to understand

It wil also help in irrigation department for farmers to control temperature

Features-

Microcontroller 8051 or PIC controller

LCD display

Sensors

·        Moisture

·        LDR

·        Temperature

Hardware required-

8051 programmer universal kit

CRO 20 Mhz

Digital multimeter

Software required:

Keil software- Microvision 2- we will use keil software to compile and

simulate  program file. We can write programming code in C or assembly language file

ORCAD for PCB design 10.5 – we will design layout in ORCAD software.

Proteus for simulation 7.4 version- we will use proteus softw

In this project we will make project on Automatic home garage using embedded system .if any car will come, it will have its unique electronics  ID. Garage shutter will automatically open for  car. For car detection we will use RFID. When  car will come garage will automatically open.

Microcontroller provide a signal to the motor circuit. Motor is not directly connected with the microcontroller. For the safety of the main processor we interface the motor with optocoupler circuit. Here we use pc 817 ( 4 pin opto coupler) to interface the micro controller with  the motor circuit. We use H bridge circuit with the motor. H bridge basically control the movement of the motor. With the help of this H bridge we change the direction of the motor. We use four transistor circuit with each motor. We are using four transistor circuit. Out of these four transistor  two transistor is NPN and two transistor and PNP transistor.  One NPN and One PNP provide a one direction voltage and motor moves on one direction. Second NPN and second PNP transistor again change the direction of the motor automatically.

Micro-controllers:

Look around. Notice the smart “intelligent” systems? Be it the T.V, washing machines, video games, telephones, automobiles, aero planes, power systems, or any application having a LED or a LCD as a user interface, the control is likely to be in the hands of a micro controller!

Measure and control, that’s where the micro controller is at its best.

Micro controllers are here to stay. Going by the current trend, it is obvious that micro controllers will be playing bigger and bigger roles in the different activities of our lives.So where does this scenario leave us? Think about it……The world of Micro controllersWhat is the primary difference between a microprocessor and a micro controller? Unlike the microprocessor, the micro controller can be considered to be a true “Computer on a chip”.

In addition to the various features like the ALU, PC, SP and registers found on a microprocessor, the micro controller also incorporates features like the ROM, RAM, Ports, timers, clock circuits, counters, reset functions etc.

While the microprocessor is more a general-purpose device, used for read, write and calculations on data, the micro controller, in addition to the above functions also controls the environment.

We have used a whole lot of technical terms already! Don’t get worried about the meanings at this point. We shall understand these terms as we proceed further

For now just be aware of the fact, that all these terms literally mean what they say.

Bits and Bytes

Before starting on the 8051, here is a quick run through on the bits and bytes. The basic unit of data for a computer is a bit. Four bits make a nibble. Eight bits or two nibbles make a byte. Sixteen bits or four nibbles or two bytes make a word.1024 bytes make a kilobyte or 1KB, and 1024 KB make a Mega Byte or 1MB.Thus when we talk of an 8-bit register, we mean the register is capable of holding data of 8 bits only.

The 8051
The 8051 developed and launched in the early 80`s, is one of the most popular micro controller in use today. It has a reasonably large amount of built in ROM and RAM. In addition it has the ability to access external memory.

The generic term `8×51` is used to define the device. The value of x defining the kind of ROM, i.e. x=0, indicates none, x=3, indicates mask ROM, x=7, indicates EPROM and x=9 indicates EEPROM or Flash.

A note on ROM

The early 8051, namely the 8031 was designed without any ROM. This device could run only with external memory connected to it. Subsequent developments lead to the development of the PROM or the programmable ROM. This type had the disadvantage of being highly unreliable.

The next in line, was the EPROM or Erasable Programmable ROM. These devices used ultraviolet light erasable memory cells. Thus a program could be loaded, tested and erased using ultra violet rays. A new program could then be loaded again.

An improved EPROM was the EEPROM or the electrically erasable PROM. This does not require ultra violet rays, and memory can be cleared using circuits within the chip itself.

Finally there is the FLASH, which is an improvement over the EEPROM. While the terms EEPROM and flash are sometimes used interchangeably, the difference lies in the fact that flash erases the complete memory at one stroke, and not act on the individual cells. This results in reducing the time for erasure.

Understanding the basic features of the 8051 core

Let’s now move on to a practical example. We shall work on a simple practical application and using the example as a base, shall explore the various features of the 8051 microcontroller.

The positive side (+ve) of the battery is connected to one side of a switch. The other side of the switch is connected to a bulb or LED (Light Emitting Diode). The bulb is then connected to a resistor, and the other end of the resistor is connected to the negative (-ve) side of the battery.

When the switch is closed or ‘switched on’ the bulb glows. When the switch is open or ‘switched off’ the bulb goes off

If you are instructed to put the switch on and off every 30 seconds, how would you do it? Obviously you would keep looking at your watch and every time the second hand crosses 30 seconds you would keep turning the switch on and off.

Imagine if you had to do this action consistently for a full day. Do you think you would be able to do it? Now if you had to do this for a month, a year??

No way, you would say!

The next step would be, then to make it automatic. This is where we use the Microcontroller.

But if the action has to take place every 30 seconds, how will the microcontroller keep track of time?

Execution time

Look at the following instruction,
clr p1.0

DC motors:

These are the motors that are commonly found in the toys and the tape recorders. These motors change the direction of rotation by changing the polarity. Most chips can’t pass enough current or voltage to spin a motor. Also, motors tend to be electrically noisy (spikes) and can slam power back into the control lines when the motor direction or speed is changed.

Specialized circuits (motor drivers) have been developed to supply motors with power and to isolate the other ICs from electrical problems. These circuits can be designed such that they can be completely separate boards, reusable from project to project.

A very popular circuit for driving DC motors (ordinary or gearhead) is called an H-bridge. It’s called that because it looks like the capital letter ‘H’ on classic schematics. The great ability of an H-bridge circuit is that the motor can be driven forward or backward at any speed, optionally using a completely independent power source.

This circuit known as the H-bridge (named for its topological similarity to the letter “H”) is commonly used to drive motors. In this circuit two of four transistors are selectively enabled to control current flow through a motor.

opposite pair of transistors (Transistor One and Transistor Three) is enabled, allowing current to flow through the motor. The other pair is disabled, and can be thought of as out of the circuit.

By determining which pair of transistors is enabled, current can be made to flow in either of the two directions through the motor. Because permanent-magnet motors reverse their direction of turn when the current flow is reversed, this circuit allows bidirectional control of the motor.

It should be clear that one would never want to enable Transistors One and Two or Transistors Three and Four simultaneously. This would cause current to flow from Power + to Power – through the transistors, and not the motors, at the maximum current-handling capacity of either the power supply or the transistors. This usually results in failure of the H-Bridge. To prevent the possibility of this failure, enable circuitry as depicted in Figure is typically used.

In this circuit, the internal inverters ensure that the vertical pairs of transistors are never enabled simultaneously. The Enable  input determines whether or not the whole circuit is operational. If this input is false, then none of the transistors are enabled, and the motor is free to coast to a stop.

By turning on the Enable input and controlling the two Direction inputs, the motor can be made to turn in either direction.

Note that if both direction inputs are the same state (either true or false) and the circuit is enabled, both terminals will be brought to the same voltage (Power + or Power – , respectively). This operation will actively brake the motor, due to a property of motors known as back emf, in which a motor that is turning generates a voltage counter to its rotation. When both terminals of the motor are brought to the same electrical potential, the back emf causes resistance to the motor’s rotation.