MICROWAVE OVENUsing

microcontrollerBy-

Manish Bhagat

CONTENTS• Introduction• Principle• Discovery• Working• Components of microwave oven• The DS1620 Digital Thermostat• Algorithm  of the

devices operation. • Health Effects

What is microwave radiation?

Microwaves radiation are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter; with frequencies between 300 MHz and 300 GHz .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.

INTRODUCTION• A 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

Discovery

Cooking 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 oven

Magnetron capable of emitting microwaves of a frequency of 2,450 GHz and a power of 700/800W

 HV transformer (for converting voltage from 220/110V to 4kV)

Temperature sensor for controlling the actual heat generated by the magnetron

Keyboard (4x4 matrix keyboard) LED/LCD display 8051 Microcontroller 

Interfacing of a Keyboard The 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 pre programmed options(6 associated just with time, 2 with weight).

Keyboard Interface

The DS1620 Digital Thermostat

The 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

Interface

Algorithm  of the devices operation.

After power up and reset, the oven waits for user input. The clock starts counting up and displaying time on the LED display .

After each pressing of a key, updated data is sent to the LED display to correspond with the user input.

When the time and power settings are in the program memory, the device waits for the 'start' button to be pressed to execute the operation.

When Interrupt 1 goes low, we resume normal operation.

When Interrupt 0 is raised (which implies, that the temperature within the microwaves cavity is too high), the magnetron output is set to 'Low‘

The keys are kept inactive while a program runs. Only pressing stop once stops the execution

Harmful Effects• microwave can strip away its original nutrients.

• Microwaves Destroy Breast Milk And Vitamin B-12

• Microwaves Create Carcinogens In Food when food is wrapped by the plastic which is heated by the microwave oven.

• Microwaves Can Change Your Heart Rate

Thank you