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MICROWAVE OVENUsing microcontroller

By-Manish Bhagat

CONTENTSIntroductionPrincipleDiscoveryWorkingComponents of microwave ovenThe DS1620 Digital ThermostatAlgorithmof the devicesoperation. Health Effects

What is microwave radiation? Microwavesradiation are a form ofelectromagnetic radiationwithwavelengthsranging from one meter to one millimeter; withfrequenciesbetween 300MHz and 300GHz .It is lie between radio and infrared frequency.

What is magnetron?Magnetron is a tube in which electrons are affected by magnetic and electric fields in such a way to produce micro wavelength radiation.

INTRODUCTIONA microwave oven, is a kitchen appliance that can come in many different sizes and styles employing microwave radiation primarily to cook or heat food. This is accomplished by using microwaves, almost always emitted from a magnetron, to excite water (primarily) and other polarized molecules within the food to be heated. This excitation is fairly uniform, leading to food being heated everywhere all at once

Microwave oven works by passing non-ionizing microwave radiation, usually at a frequency of 2.45 GHz (a wavelength of 12.24 cm), through the food.. Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating. Many molecules (such as those of water) are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. This molecular movement creates heat as the rotating molecules hit other molecules and put them into motion. Microwave heating is most efficient on liquid water, and much less so on fats and sugars (which have less molecular dipole moment), and frozen water (where the molecules are not free to rotate). PRINCIPLE

DiscoveryCooking food with microwaves was discovered by PERCY SPENCER while building magnetrons for radar sets. He was working on an active radar set when he noticed that a peanut chocolate bar he had in his pocket started to melt. The radar had melted his chocolate bar with microwave. Then he cooked popcorns and food in microwave . Spencer created a high density electromagnetic field by feeding microwave power into a metal box which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly.

Every microwave oven contains a magnetron, a tube in which electrons are affected by magnetic and electric fields in such a way to produce micro wavelength radiation. This microwave radiation interacts with the molecules in the food. All wave energy changes polarity from positive to negative with each cycle of the wave and this cause the polar molecules to rotate at the same frequency millions of times a second. All this agitation creates a molecular friction within the food and at last this heats up the food.WORKING

Components of microwave ovenMagnetroncapable of emitting microwavesof afrequency of 2,450 GHzand apowerof 700/800W HVtransformer(forconverting voltage from220/110V to4kV) Temperature sensorforcontrolling the actualheat generated by the magnetronKeyboard (4x4 matrix keyboard) LED/LCDdisplay 8051 Microcontroller

Interfacing of a KeyboardThe sole purpose of keyboard application is the need to incorporate the user input.

4 keys are used for inputting the time (10min,1min,10sec,1sec, pressing each of these adds an appropriate amount of memory to the timer counter), 2 for inputting the weight of the material to heat (1kg,100g), 1 for stop and 1 for start, and the remaining 8 for the preprogrammed options(6 associated just with time, 2 with weight).

Keyboard Interface

The DS1620 Digital ThermostatThe DS1620 Digital Thermostat provides 9-bit temperature readings. It has three alarm outputs, so the device can also act as a thermostat. The DS1620, which incorporates a 3-wire interface can be controlled using an 8051 Microcontroller

Temperature Control of the DS1620

The thermostat outputs of the DS1620 allow it to directly control heating and cooling devices.The output THIGH can be used to indicate that a high temperature tolerance boundary has been met or exceeded, or it can be used as part of a closed loop system to activate a cooling system and deactivate it when the system temperature returns to tolerance.TLOW is driven high when the temperature of the device falls below the limit set in the TL Register. TLOW remains active until the DS1620's temperature becomes greater than the value stored in the low temperature register, TL.

A Digital Thermostat Interface


Algorithmof the devicesoperation. Afterpowerup and reset, the ovenwaitsforuserinput. The clock starts counting up and displaying time onthe LEDdisplay .Aftereachpressing of akey, updated dataissent tothe LED display tocorrespond withthe userinput.Whenthe time and powersettingsare inthe programmemory, the device waitsforthe 'start' buttontobe pressed toexecute the operation.

WhenInterrupt 1 goeslow, we resume normal operation.WhenInterrupt 0 israised (whichimplies, that the temperature within the microwavescavity istoohigh), the magnetronoutput is set to 'LowThe keysare kept inactive while aprogramruns. Only pressing stop once stopsthe execution

Harmful Effectsmicrowave can strip away its original nutrients.Microwaves Destroy Breast Milk And Vitamin B-12Microwaves Create Carcinogens In Food when food is wrapped by the plastic which is heated by the microwave oven.Microwaves Can Change Your Heart Rate

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