What is a Control System?

A Control System is about providing a System with certain Controls to enable it run and perform functions.

A control system: manages; commands; directs or regulates the behavior of other devices or systems It can range from a home heating controller using a thermostat controlling a domestic boiler to large Industrial control systems which are used for controlling processes or machines.

They follow the simple Input>Process>Output routine like most computers.

A simple example of a control system could be switching the lights on:

  • Switch > input
  • Wires/Connection > Process
  • Light Bulb > Output

or a Pelicon Crossing:

  • Crossing Button > Input
  • Change of Lights > Process
  • Lights, Buzzer, Green Man > Output


An input in this context can only be two types, a Switch or a Sensor.


A switch can either be on or off, but once the state is switched, it will stay that way until switched back.

A Button it the same as a switch however, it has to be held for the change in state. Once release it will automatically revert to its previous state.

Tilt Switch is a switch that will change state when it is tilted over a certain angle. A good example of this is in a car. The alarm will be triggered if the car is moved, however if it is tilted over a certain angle a switch turns the alarm off. This is because it thinks it is being towed.


Sensors are used to measure physical quantities such as temperature, light, pressure, sound, and humidity. Some examples of sensors:

  • A security alarm system may have an infrared sensor which sends a signal when the beam is broken.
  • A heat sensitive sensor in the corner of a room may detect the presence of a person.
  • Temperature sensors could be used to control the heating in a large building.
  • Magnetic sensors are used to detect metal and can be placed in roads to monitor traffic flow.


A normal computer has no way of affecting what is happening around it. It can’t turn on the lights, or make the room hotter. How do we change what is happening around us?

We can give it the ability to do lots of things by connecting a range of actuators to it. An actuator is a device, controlled by a computer, that can affect the real-world.

Actuator What it Can Do
Light bulb or LED Creates light
Heater Increases temperature
Cooling Unit Decreases temperature
Motor Spins things around
Pump Pushes water / air through pipes
Buzzer / Bell / Siren Creates noise


Flowol is a piece of software that lets you learn about control by creating flowcharts and then running the control program represented by the flowchart. By using special animations called Mimics, you can see a realistic imitation of a real situation, such as a traffic light simulation or level crossing.

I used Flowol to create a series of flow control programs, that simulate a few different scenarios. You can see some examples of the program running opposite.