2. Definitions of Control Systems
A control system is a collection of components working
together under the direction of some machine intelligence.
In most cases, electronic circuits provide the intelligence, and
electromechanical components such as sensors and motors
provide the interface to the physical world.
4. Parts of Control System
Every control system has (at least) a controller and an actuator (also
called a final control element).
The Controller is the intelligence of the system and is usually
electronic.
The input to the controller is called the Set point, which is a signal
representing the desired system output.
The Actuator is an electromechanical device that takes the signal from
the controller and converts it into some kind of physical action.
Examples of typical actuators would be an electric motor, an electrically
controlled valve, or a heating element.
The last block is labeled Process and has an output labeled Controlled
variable. The process block represents the physical process being
affected by the actuator, and the controlled variable is the measurable
result of that process.
5. Control System Classifications
Open-Loop Control Systems:The controller never actually
knows if the actuator did what it was supposed to.
Closed-Loop Control Systems: The output of the process
(controlled variable) is constantly monitored by a sensor.
6. Microcontrollers
The microcontroller is simply a computer on a chip.
A microcontroller differs from microprocessor; it usually
includes a central processor (CPU), input and output ports,
memory for program and data storage, an internal clock, and
one or more peripheral devices such as timers, counters,
analog-to-digital converters (ADC) and serial
communication facilities.
8. PIC Microcontrollers
PIC is the name for the Microchip microcontroller (MCU)
family, consisting of a microprocessor, I/O ports, timers and
other internal, integrated hardware. The main advantages are
low external part count, a wide range of chip sizes great
availability of compilers and source code and easy
programming.
In our course we’ll use the Microchip products (PIC16F877A)
microcontroller.
9. PIC16F877A Features
o High-performance RISC CPU
o 8 Kbytes of FLASH Program Memory
o 368 bytes of Data Memory (RAM)
o 256 bytes of EEPROM Data Memory
o 33 I/O pins: (5 ports: A(6), B(8), C(8), D(8) and E(3))
o 4-20 MHz operating speed
o Wide operating voltage range: 2.0V to 5.5V.
o Max. 25 mA current from an output pin.