| Intermediate Technology Education | Control Technology | Pre-Design | Topic 3 | Activity 8 |

Computer Control Systems

Computer control is the most powerful and flexible method to control a wide variety of processes and mechanisms.  Computer control systems are employed in almost all modern technological products.
  • Learn the basic concepts of computer control
  • Learn the basic components required for computer control
  • Investigate examples of computer control
Computer control does the same things that other forms of control do—it accepts inputs, it process them, it produces outputs, and it can monitor the inputs and outputs to ensure that control is maintained over time.  The following section looks at the building blocks of computer control, as it applies to this module.

Basic Concepts and Components

The following example illustrates basic computer control components and concepts. An explanation follows the figure.


Figure Computer Control Model

Explanation

  • The Components
    • The switch is an input device that a person uses to communicate with the computer program operating the interface.
    • The motor is an output device that is operated (controlled) by the interface based on commands from the computer program.  Other output devices could also be used
    • The power source is used to run the motor.  It is controlled by the interface based on commands from the computer program.  Some interfaces can control multiple output devices,  and can send electricity to any combination of them at the same time.
    • The interface translates between the computer and its program, and the input and output devices attached to it.  It accepts input from the input devices and sends it to the computer.  It takes instructions from the computer and sends it to the output devices.
    • By running a purpose-build software program, the computer can listen to the interface for inputs.  When it gets them, it can respond and send signals back to the interface to affect the outputs, turning them on and off, or making them change, for example speed up the motor or slow it down.  Of course, the program can be designed so that a person can manipulate on-screen controls and turn the motor on or off directly (or change its speed)
  • Operation of the System
    • In this example, turning the switch on causes the interface to get an input signal.  The interface alerts the computer program about the input (what it is and what it came from). 
    • The program makes a determination what to do about the input.  It sends a signal to the interface instructing it to turn on the motor. 
    • The interface directs electricity from the power source to the motor
    • The motor receives the output from the interface (in the form of electrical power) and begins to spin.

Computer Control Components

This module uses the following computer control components.  Additional ones may be used if desired.

Interface 

Phidgets Motor Control.  This interface can be used to control motors, lights, and LEDs.  It has 4 inputs for digital devices such as switches.  It has 2 outputs to control two devices simultaneously. It has a USB connector to connect to a USB port in the computer, and it has a power supply input that can take from 5 to 9 volts DC.  The power supply is used to supply electricity to the outputs.  The interface itself gets its power from the computer.  The following pictures illustrate the interface.


Figure Phidgets Motor Controller

Figure Phidgets Connectors

Figure Phidgets Inputs and Outputs

DC Motors

Two DC motors are supplied.  The picture below shows them mounted on a chassis. If you look closely you can see through the clear plastic housing and find the motor and the plastic reduction gears.


Figure Geared DC Motors

Cables and Power Supply

There should be a ribbon cable with 4 wire strands, a USB cable and a 6 Volt DC power supply.


Figure Cables and Power Supply

In addition a set of wheels are supplied for the motors, along with friction bands which need to be mounted on them.

Examples of Computer Control

The following examples of computer control employ the kit of parts described above.

Computer Controlled Motor

This example uses the Phidgets Motor Control interface and one of the motors from the supplied kit.  One of the wheels is mounted on the shaft and has a mark so that rotation is clearly visible.  The motor is being controlled by a Visual Basic program which appears as an inset on the video clip. A person is manipulating the sliders in the program.


Video Computer Controlled Motor

Computer Controlled Lights

This example uses the Phidgets Motor Control interface and two lights.  In the first part, two incandescent bulbs are used.  In the second part, two LEDs (light emitting diodes) are used.  The same program is used in both cases.  If you look closely you can see the pointer move as the person manipulates the screen controls to modify the light settings.  As you can see, the two outputs can be controlled independently.


Video Computer Controlled Lighting

Computer Controlled Buggy

This example uses the Phidgets Motor Control interface and two of the DC motors with wheels mounted on them.  The motors are mounted on a plastic chassis, and a roller is mounted at the other end.  A post is used to hold the ribbon cable up higher and out of the way of the wheels


Video Computer Controlled Buggy

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