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Abstract and Result should be accompanied with the report in a separate paper. 





Domestic and Business telephone users in Sri Lanka are not provided with a detailed listing of outgoing telephone calls. The detailed listing is very important owing to the fact of rising telephone call charges and in turn an additional burden on subscriber.


By using ITDL subscribers can formulate their own telephone management criteria in order to minimize call duration and unnecessary calls. This is because the call charges are varying depending on time a call started and the number of unit consumed. In addition, a subscriber can locate any unauthorized calls originated by the telephone in the absence of him or her.


ITDL has a storing capacity of around 600 telephone calls. For domestic use this is normally the usage of two months and for office usage it is advisable to take print outs each month and reset the system to leave room for storing more call information.


Subscriber can easily plug in ITDL to his telephone and to main power. The system has a very simple operating system. Further, it can run as a stand along system, even in the absence of main power. It needs little maintenance. ITDL can be kept alongside the telephone or else in a place, which are cool, dry and dust free. 


The report covers most of the design that I thought vital to be documented. It starts with a project overview to its main components and highlights the design approach. The subsequent sections explain the design and operational aspects in detail.




After working on the project for quit a while and achieving most of the goals, I am pleased with the attained success and the challenges overcame in meeting the project objectives. In this project, I was able to incorporate the Z80 microprocessor with externally built hardware and make it perform to specification. The project provided me with a strong background for similar tasks I might undertake in the field of microprocessor in the future. I was able to place myself in an almost real situation of electronic product design and implementation and learn the steps involved in such a process. Specific to my project, I was able to prove that the idea of fetching the telephone number and associate timing function scenario I have described in the previous sections, are quite feasible


I learned that various problems can occur when interfacing the Z80 with a hardware setup. In my case, timing was a very critical factor. However, the Z80 can handle these time intensive applications if provided with a suitable external hardware.

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Full circuit diagram of the the ITDL which was drawn using Visio professional.


The above diagram can be opened on Visio environment. then copy it to the page 22 which is not included in the site

Download Visio

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PCB layout was drawn using Expresspcb ver 2.6.2 You can download the software free of charge at


The PCB layout can be opened on ExpressPCB  environment. then copy it to the page 23 which is not included in the site 



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Last modified: July 13, 2002