dtmf decoder

  
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The main system is the user interface and control system. The phone line was chosen as the method of interfacing because it has distinct advantages over other systems in communicating information from a distance. The next image serves as a block diagram for not only the remote access interface but the overall system as a whole. System flow and act
dtmf decoder - schematic

ivation begins at the top left of the block diagram with the answering machine picking up a call from the user dialing in remotely. The answering machine controls the connection and disconnection of the phone line to the DTMF decoder automatically. The user presses the keys on their touch tone enabled telephone in a specific sequence. The DTMF decoder circuit is connected to the phone line and it interprets the DTMF signals on the line and forwards them to the main microcontroller in the form of a four bit binary number. The controller running the main firmware determines if the correct input sequence was entered by the user and interfaces directly with the individual subsystems. The subsystems also have a local activation capability such as a pushbutton switch to control its functionality. The subsystems are independent of one another and can operate in parallel if an activation signal is given from either the controller or from the local activation switches. The RS-232 interface with the computer and the decoded DTMF display are both examples of future work for the system and are not implemented on the prototype. The open air microphone also shown in the block diagram has been removed for lack of relevance and because of the noise it introduces on the line. The flow of the microcontroller software is shown below. When a user dials into the system remotely they are in the user interface portion of the system flow. DTMF...



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