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Facsimile serial and parallel telephone connection

2016-02-02 08:00  
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There are two methods by which a telephone may be connected: serial telephone connection and parallel telephone connection. Either method allows the same telephone line to be used for voice and facsimile communication.When the handset is lifted and power is applied to the circuit, Q2 is fed base current through R2, which in turn drives Ql. C2 is charged via R3 in series with D1 to (Vz1 -0. 7) V. When the minimum operating Vnv voltage is reached, power on reset occurs via the rc network of Cl and RS. Q2 is maintained in the on condition by Gl, while Q3, and hence Q4, are held off by G2. The DF320 network appears in parallel with the telephone as an impedance more than 10 KO in the standby condition with the telephone network connected in circuit through Ql.On recognition of the first keyed digit, the DF320  clock is started. Ml then goes to logic I causing Q2 and Ql to tum off, and Q3 and Q4 to tum on. Hence, the majority of the line loop current now flows through Q4 and Zl. When impulsing occurs, Q3 and Q4 are turned off by DP acting on G2. Line loop current is then reduced to approximately 50 f`A taken through R2, R4, and G2 in series. When dialing in, complete Ml goes to logic 0, causing the telephone network to be reconnected. This Project can be used in houses and offices in which more than one telephone is connected in parallel through a single telephone line Our project is used to connect a maximum of four telephones in parallel. When any one of the phone is lifted, all the other lines are disconnected from the telephone line.The above condition is also applicable when the telephone ring arrives only one telephone which is connected to the telephone line which is lifted first, while the other three lines are disconnected from the telephone line.