Microprocessor Control of a Microwave Oven
In this presentation you will:
 see how a microprocessor controls a microwave oven
Microprocessor Control of a Microwave Oven
The Microprocessor
Many gadgets, devices, appliances and machines have
microprocessors controlling their operation.
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Microprocessor Control of a Microwave Oven
Input Devices
Process
Output Devices
For a microprocessor to control
device, it has to:
 Detect changes
occurring in the system
using input devices.
 Make decisions
based on the
detected changes.
 Activate appropriate
output devices according
to decisions made.
Microprocessor
Controller System
Input
Process
Output
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Microprocessor Control of a Microwave Oven
Input / Output
Microprocessors control devices using an input/output interface.
Fan
Address Bus
Output
Output
Interface
Microprocessor
RAM
ROM
I/O
Input
Interface
Input
Data Bus
Control Bus
Temperature
Sensor
There is an output interface for actuating external devices like a motor, and
an input interface to monitor external devices like a temperature sensor.
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Microprocessor Control of a Microwave Oven
Microprocessor Control
Microwave ovens use microprocessors to control their operation.
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Microprocessor Control of a Microwave Oven
Components
Here are some of the devices are used in a microwave oven:
 A microwave generator
produces the microwaves
that cook the food.
 A lamp illuminates during
the cooking process.
 A motor drives a turntable
so that the food rotates and
cooks evenly.
 A display indicates the
cooking time and the
selected cooking mode.
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Microprocessor Control of a Microwave Oven
 A sounder beeps when the
cooking period is complete.
 The keypad enables the cooking
time to be set, cooking mode to
be entered and START/STOP
cooking selected.
 A door switch detects when the
door is open.
 A fan removes steam that is
generated by cooking.
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Microprocessor Control of a Microwave Oven
To control the operation of the microwave oven, there is a printed circuit
board (PCB) containing the microprocessor system.
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Microprocessor Control of a Microwave Oven
To power the microprocessor and the
various devices, the microwave oven
is connected to the power source.
The power source is a high voltage,
alternating current (AC) supply.
The circuitry of the microprocessor
and some of the devices require a
lower, direct current (DC) voltage.
A power supply unit converts the AC supply
to the required DC voltage level.
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Microprocessor Control of a Microwave Oven
Input Devices
The INPUT devices to the
microprocessor system are:
 The keypad
 The door switch
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Microprocessor Control of a Microwave Oven
Door Switch
The door switch requires one input line to the microprocessor system.
The input line is a wire that carries an
electrical signal from the door switch
to the microprocessor system.
The switch could be in one of two
positions.
With the door open the switch would
be open, and with the door closed
the switch would be closed.
The microprocessor can determine the position of the
switch by the electrical signal on the input line.
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Microprocessor Control of a Microwave Oven
Keypad
The keypad has many buttons
and requires several lines
connecting it to the
microprocessor system.
For each button pressed on the
keypad, a unique digital code is
sent to the microprocessor.
In this way the microprocessor is
able to detect which button has
been pressed.
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Microprocessor Control of a Microwave Oven
Output Devices
The output devices from the
microprocessor system are:
 Microwave generator
 Turntable motor
 Display
 Lamp
 Sounder
 Fan
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Microprocessor Control of a Microwave Oven
The microwave generator, turntable
motor, lamp, sounder and fan each
require single line OUTPUTS from
the microprocessor.
The microprocessor can activate
any one of the output devices by
sending an electrical signal. For
example, to switch the lamp on.
There are several outputs from the
microprocessor to the display, so
that numerous message options
can be illuminated.
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Microprocessor Control of a Microwave Oven
Question 1
Which device is an input to the microprocessor?
A) lamp
B) fan
C) keypad
D) microwave generator
Microprocessor Control of a Microwave Oven
Question 2
What device generates the low DC voltage?
A) Fan
B) Microwave Generator
C) Microprocessor
D) Power Supply
Microprocessor Control of a Microwave Oven
Here are the input and output connections to and from the microprocessor.
The connections become confusing to follow when shown all together.
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Microprocessor Control of a Microwave Oven
If the microprocessor and devices are taken out of the cabinet, we can
view the connections more easily.
One last important
element of the system is
a TIMER for timing the
cooking period.
An electronic timer is
usually an integrated
circuit on the
microprocessor board.
Timer
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Microprocessor Control of a Microwave Oven
Question 3
Which output device requires more than one control line from the
microprocessor?
A) Lamp
B) Microwave Generator
C) Turntable Motor
D) Display
Microprocessor Control of a Microwave Oven
System Operation
The cooking mode is
selected on the keypad and
the cooking period set.
The microprocessor reads
the settings input on the
keypad into its memory.
Signals are sent to the
display to indicate the
cooking mode and cooking
period set.
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Microprocessor Control of a Microwave Oven
Question 4
The cooking mode setting, entered on the keypad, is stored
in which of the following?
A) In the display
B) In the microprocessor's memory
C) In the microwave generator
D) In the power supply
Microprocessor Control of a Microwave Oven
Processing Input
If the START button is
pressed while the door
switch is open, the
microprocessor will detect
this and prevent cooking.
Not until the door is shut,
will the computer allow
cooking to begin.
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Microprocessor Control of a Microwave Oven
When the START button is pressed and the door is shut,
the microprocessor carries out the following:
 Starts the electronic timer with
the cooking period
 Switches the fan on
 Switches the lamp on
 Starts the turntable motor running
 Switches the microwave generator on
The microprocessor is able to carry out these tasks very
quickly so they appear to happen at the same time.
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Microprocessor Control of a Microwave Oven
The electronic timer counts
down during the cooking
period. The microprocessor
updates the display every
time a second passes.
The microprocessor checks
for changes which might
occur, for example, the door
being opened or the stop
button being pressed.
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Microprocessor Control of a Microwave Oven
If the door is opened, the microprocessor will detect it and stop the cooking
process by switching off the fan, microwave generator and turntable motor.
It may also put a message on the display, DOOR OPEN.
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Microprocessor Control of a Microwave Oven
If the cooking mode is
set to full power, the
microwave generator
will be on continuously.
When the mode is set
to defrost, the
microprocessor will
switch the microwave
generator on and off
repeatedly during the
cooking process. The
average cooking
power will be less.
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Microprocessor Control of a Microwave Oven
When the cooking period is
complete, the microprocessor
will switch off the fan,
microwave generator, lamp
and turntable motor.
It will then switch the sounder
on to let the user know that the
cooking cycle is complete.
When the door is opened, the
microprocessor switches the
sounder off if it is still sounding.
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Microprocessor Control of a Microwave Oven
Question 5
What component tells the microprocessor the cooking period is
complete?
A) Input Interface
B) Output Interface
C) Timer
D) Memory
Microprocessor Control of a Microwave Oven
Many other devices use a microprocessor to read input devices,
make decisions and control output devices such as:
 Washing machines
 Central heating systems
 Games consoles
 Vehicle engine
management systems
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Microprocessor Control of a Microwave Oven
Summary
In this presentation you have seen:
 how a microprocessor can control the various devices of
a microwave oven
 how a microprocessor can read input devices, make
decisions and control output devices.
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