Contact-ID Protocol Interface Circuit

OData support
Lazányi János Gyula
Department of Measurement and Information Systems

The subject of my thesis is to implement the Contact ID protocol in an embedded environment.

As stated in the description of the topic, this type of communication protocol is primarily used by today’s alarm systems. In the case of the Contact ID protocol, data transmission is implemented via a telephone line with the help of DTMF (Dual-Tone Multi-Frequency) signals. I used the hardware of the Open USB FXS open source project, to implement the protocol. The objective of the project was to create an instrument which would enable analogue telephones to communicate over VOIP (Voice Over IP). The reason why I have chosen this equipment is that on the one hand, it is capable of detecting and handling the signals arriving via telephone lines, and on the other hand it can also be connected to computers through a USB port. It was also in favour of this equipment that the hardware was easy and cheap to assemble.

In subsequent chapters I provide details of the PIC18F2550 microcontroller, which is responsible for the functioning of the equipment, as well as of the SI3210 chip, which controls the telephone line. Furthermore, I also elaborate on how the current software works and on the changes I made during the course of the development.

Lastly, I sum up my experience gained during the testing period and touch upon the sources of potential errors.


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