Control and monitoring of multiple devices via computer interface

 Control and monitoring of multiple devices  via computer interface

                                                           1James Agajo, 2 A Sylvester Ezewele  

             Department of Electrical/Electronics, Federal Polytechnic, Auchi

Edo State ,Nigeria, Email:, Phone: +2348053312732

Abstract: Control and monitoring of multiple devices  via computer interface  suggest way of  controlling  device via the internet, various interfaces were discussed,  procedure for testing was also analysed, software used were also shown

Keyword: Control, switch, microcontrollers, computer


There has been continuous quest for man to improve his well being through, reactions to problems and challenges posed by his environment. Over the years, computer and computer communication had gained so much attention and grown tremendously, reducing big and expensive mainframes into small and affordable devices. Statistics have shown that most people spend most of their time on computers, since most of their activities locally or globally over a network. Since much time is spent on computer system, it becomes necessary to design a device for controlling switches from computer. Switches are so essential that one can not avoid to use them on a daily basis for putting on or turning off electrical devices, and as a result of these, many devices have been designed by man to help him conquer these problems and challenges posed by physical contact with electricity. The switch control system can range from simply controlling of light without leaving a seat, to being able to switch on industrial electrical devices through a computer. There has to be an interface between industrial electrical devices and a controller, the PC in this case. Interface are required so that the PC can communicate with other devices (Osinuga and oresotu 2001), the interface used in this work is the computer port interface. The microprocessor switch control system is made up of several devices connected together; keypads that transmit commands to the device, fixtures controller that is programmed to on the appliances automatically via a computer system. [1]


Yong- Jing Nu (1998), observed that microprocessor based toggle switch control system is primary configured with a power factor corrector (PFC), a square- ware voltage generator, a manually controlled toggle switch and two relay. Toggle switch can select a different number of lamps in operation, resulting in a manual dimming feature.[2]


Software Engineering has internationally accepted software Engineering standards for transforming ideals into an inference engine. They include:

v     The structured system Analysis and Design methodology (SSADM)

v     Prototyping

v     Experts system methodology

v     Usability Engineering methodologies, etc.

The methodology applied in the system is prototyping and is discussed below.

3.0 duction                                                PROTOTYPING

In electronics, prototyping means building an actual circuit to a design to verity that it works, and to provide a physical plat forms for debugging it, it does not work. Prototyping sometimes converts intangible specifications into a tangible but limited working model of the desired information system. [3]


System prototypes could be classified into:

  1. Evolutionary prototype:  This design is adapted for permanent use after the ideas are clarified and must be built using the program tools that will be used for the final system.
  1. The throwaway prototype: This design is to be discarded after utilization, basically it is to test ideas and is especially useful for comparing alternative designs for part of a system.[3]


  1. Identify the user’s known information requirements and features needed in the system.
  2. Develop a working prototype.
  3. Use the prototype, noting need enhancements and changes; this expands the list of known system requirements.
  4. Revise the prototype based on information gained through user experience.
  5. Repeat these steps as needed to achieve a satisfactory system.


  1. Requires user involvement.
  2. It helps to refine the potential risks associated with the delivery of the system being developed.
  3. Prototyping facilitates system implementation since users know what to expect and exposed developers to potential future system enhancements.
  4. User can point to features they like or dislike and so indicate shortcomings in an existing and working system more easily, and then they can describe them in a theoretical or proposed system.[4]


              I.      The process of developing a prototype can cause systems to be left unfinished or implemented before they are ready.

            II.      Prototyping can sometimes leads to incomplete documentation and insufficient analysis.

          III.      The process of developing a prototype may require greater involvement and commitment by key users who are already busy with their regular work.

         IV.      If sophisticated software prototypes are employed, the time saving benefit of prototyping can be lost.

           V.      In prototyping, structure of system can be damaged since many changes could be made and it is not suitable for large applications.

Our prototype in this project is constructed using a microprocessor to control electrical appliances.[5]


The present procedure involves a manual control of the power switch by the industrial electrician. The power control switch is operated with hand by pushing the switch lever to on position if it’s intended to be turned on or off position if it’s intended to be turned off. Basically, during the analysis of this procedure, it is discovered that the operators is at high risk of been electrocuted. Manually, switches have been existing for many years in every home, industry, company, schools and colleges. [6]

These switches are in different standards such as:

  1. ON- OFF e.g. toggle switches – it is used to switch the power supply of a circuit. When used with mains electricity, this type of switch must be in the lives wires.
  2. (ON – OFF) push- to- make switch is for doorbell.
  3. (ON – OFF) push- to- break switch is also for doorbell.

This switch can be “ON” in both positions, switching on a separate device. In each case, it is often called a change over switch example; a SPOT switch can be used to switch ON red lamp in one position and a green lamp in another position.


The contacts of a reed switch are closed by bringing a small magnet near the switch. They are used in security circuits, for example to check the doors and closed. Standard reed switches are SPST (simple ON/ OFF)


         Contacts (example single pole, double throw)

         Rating (maximum voltage and current)

         Methods of operation (toggle, slide, key etc.


v                 Electrocution: Those switches claim a lot of lives as a result of direct contact of the operator with them for example; the operator might be electrocuted in the process of carrying out power change over.

v                 Time wastage: it takes time to go from one switch to the other to ON or OFF them whenever there is power failure.

v                 Friction: friction is applied in operating these switches. Worn out switches can lead to the damage of the electrical devices which it is controlling.

v                 Frequent touching of the switch causes the damage of the switch circuit.

v                 Bad switch control might result to serious inferno to industrial equipment and other valuables.


This circuit is made up of BC 337 transistor switching circuit; each circuit is connected to a relay, a transistor and diode. The relay when activated, ON or OFF any appliance connected to it. The three lives from the microprocessor are each connected respectively to the BASE pin of the three corresponding transistor.[6]

The circuit is the heart of this module. It comprises of 9-pin Dip-male connector, Max-232, 8051 microprocessor, crystal oscillator.

 The circuit connects directly to the computer serial port through a pin cable. The MAX- 232 amplifies signal (VS) that goes into the microprocessor from the computer system through the serial cables. Serial data is transmitted from the PC as a series of positive and negative voltage on a single wire, which serial data occurred at a pre-determined time established by the base wire.

The 11-0597MHZ crystal oscillator determines the speed of the 8051 microprocessor used. The microprocessor is connected to the three BC B37A transistor that derives the three relays. Pin 2 an d3 of the serial port are connected to line 14 and 13 of the MAX- 232. [7,8]


v     Microprocessor

v     Relays

v     AC bulb

v     Capacitors

v     LEDS

v     Switches

v     Transistor

v     Resistor

v     Diode


The set up program prepares your computer to stall the software from the CD.

To install the program;

v     Insert the CD, in the CD program;

v     Double click on CD my computer

v     Double click on CD drive icon

v     Double click on setup icon

v     Follow the screen instructions to complete installation.


 How to open the software

ü      Click to view start menu

ü      Click on all program

ü      Click on control

ü      Finally click on control

 The interface will appear:

v     Check the ON/ OFF box and click on desired relay button

v     When the status is B or D or F the relays are ON, but when the status is A or C or E then the relays are OFF.


 The user’s manual for the system will accompany the software CD. The aim of this manual is to guide the users on the appropriate steps to follow[9,10]


The switch controller must be connected to the system unit. The guide on how to connect it to the computer are:

v     Insert the serial cable female port into “D- shape male 9- pins serial port at the back of system unit and screw.

v     Connect the power cable into any power source of 240V

v     Make sure the computer system cables are properly fixed.


Software or hardware testing is very important element of assurance and it represents the ultimate view of specification, design and coding. The main thing here is to execute a program with the intent to search for an error. If the program executes without any notable instate; there the objectives of conceiving it is achieved.

 However, the free flow of the software was realized by removing bugs at early stages of the software development and the hardware was also realized by proper soldering of the components used on the breadboard

The New software and hardware project shall be tested thoroughly ensure that it meets the requirements in the specification. Macro et al stated that there are five stages of system testing or levels. These include;

v     Function Testing: The functions and modules that make up the module are tested to ensure their correct operation.

v     Module Testing: The functions are combined to form a module. This module is tested to ensure that its performance meets specifications. In this design the modules, which are tested and it responds positively which shows the modules are independently efficient and reliable.

v     Integration Testing: This is some time called subsystem testing, a set of modules are integrated. As software module and hardware module interact, the testing focus is on modules interface because it is assumed that the modules themselves are correct. This test is carried out to ascertain that those modules do not loose their efficiency and reliability by integrating them into subsystems and systems.

v     Total program testing: sometimes called system testing is the level where all the testing process concentrated more on detecting errors and determining how well user’s requirement are meet.


  Microprocessor- based main switch control system, is a system consisting of software and hardware module. The hardware module is the controller circuit, which must be connected to the system unit and the software module is in a CD-ROM and needed to be installed in the system unit (hard disk). This will only take effect when the controller is properly connected to the computer system through the serial port and to the power source. Any electrical device connected to it can be switch on or off through the interface provide by the software.

Depending on the previous by the software bulbs, when the command button of any relay is clicked, signals goes from there to desirable bulb.

When relay 1 is off the status will display “A” but when it is ON, the status will display “B” .

Also when relay 2 is off the status will display “C”, when it is ON the status will display “D”.

Finally when relay 3 is off the status will display “E” but the relay is ON the status will display “F”.


This detail involves the conversion of files, parallel or pilot implementation plans. This involves the change- over procedures. Once the system has been fully designed, tested for a good percentage of perfection and accepted, the change over plan can be made. So this plan is done using the two types below:

ü      Parallel change over

ü      Pilot change over.


This system will allow the new system to continue along side with the old system, for weeks or months. The disadvantage of parallel running is the extra effort required to keep both system running.


Here, the new system is introduced into one of the department or branches of an organization and run until it is proven to be satisfactory. Then if it works with little or no shortcomings, it can then the installed in all the organizations and department or implemented fully everywhere as the case may be.

For this project both change over plans will do, but we are implementing the pilot change over plan because this new system has so many advantages over the old system.


This work is recommended to be used in industries, large firms manufacturing industries e.t.c. This is to provides easy and safe use of the electrical devices; Instructions are programmed into the microprocessor to carry out their functions. The management of any organization using this project should employ computer analyst who will be operating this system.

   The primary objectives of this project is to control electrical devices with computer through serial port was achieved successfully. The microprocessor in the control unit was programmed using assembly language.


[1] Addison, Wesley k. and Takashi 9 (1990) Power electronics for the 

microprocessor Age, Oxford University Press.

  1. [2] Alluwalia. A and yeralan: Programming and interfacing the         
  2. [3]  Anigbogu  S.O ( 1997) Basic computer electronic and logic circuits Christon      

International Company LTD, Awka.

[4] Beyond Logic (2008), Interfacing the serial RS-232 Port, (http//www.Interface com/ MAX-232/html)

[5] Boylston, R.L.,and L Nashalsky. Electronic Devices and

[6] Chris Kotoroski, (2008) A push –to – break breaks  word toggle switch.

Circuit theory. Prentice – Hal/ of India private Ltd., New Delhi, 8th edition, 2004.

[7] Douglas, V.H; Microprocessor and Interfacing” .Tata McGraw-Hill, New Delhi; 2nd Edition, 1999.

[8] Hennessy, J,L and Patterson D.A (2002),  Interfacing the serial RS-232 Port


[9] Hughes Edward; Electrical Technology, ELBS and Longman group; 4th  

Edition, 1972 8951 micro controller adhesion_ wesley,1995.

[10] Ismail, and V.M Rooney, (1987) Microprocessor Hardware and Software Concepts IT Press, Chicago.

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