Microcontrollers: A Designer's Overview
Microcontrollers Are Everywhere
Used in everything from the simplest lawn watering controller to highly sophisticated satellite systems, the microcontroller has become ubiquitous and invisible. The average U.S. household has about 60 embedded microcontrollers.1 A 1999 BMW 7-series has 65 microcontrollers.2 Over 5 billion microcontrollers are added to the mix annually. Although the microcontrollers in PCs are the most visible, they account for just 6% of of the microcontroller market.3
Where Microcontrollers are Used
In the office, microcontrollers are used in computer keyboards, monitors, printers, copiers, fax machines, and telephone systems to name a few. In your home, microcontrollers are used in microwave ovens, washers and dryers, security systems, lawn sprinkler station controllers, and music/video entertainment components.
What are Microcontrollers?
Microcontrollers are complete computer systems on a chip, typically combining an arithmetic logic unit (ALU), memory, timer/counters, serial port, input/output ports (I/O) and a clock oscillator.
Microcontrollers are used in applications requiring repetitive operations such as running the traffic light at an intersection. In this application, the microcontroller's sole function is to turn lights on and off at predetermined times.
Another example is a microwave oven. Let's examine how a microcontroller functions while cooking a bag of popcorn in a microwave oven.
You open the door and put the bag of popcorn inside. You close the door and push the button labeled "Popcorn." A few minutes later, a tone announces the popcorn is done. What happened behind the scenes?
When you opened the door, the microcontroller sensed the door switch, turned on the light and disabled the magnetron. The microcontroller continually scans the keyboard. When you pushed the "Popcorn" button, the microcontroller confirmed that the door was closed and began to count timing pulses, started the motor for the turntable, set the power level of the magnetron, and controlled the display. When the timer reached zero, the microcontroller shut down the magnetron, stopped the turntable, and signaled you.
This is a simple example of a microcontroller application. Microcontrollers are available with extra features such as analog-to-digital converters (ADCs), pulse-width modulation (PWM), watchdog timers, controller area network (CAN), and security functions.