Free Electronic Circuits & 8085 projects

Electronic projects with circuit diagram and 8085 microprocessor projects.

Small Telephone Line circuit

Published on Feb 03 2010 // Telephone Communication Circuits


Small Telephone line circuit

This circuit can be set at home or office, connected to a telephone line which receives multiple calls, and will not appear  at telephone booth monitor each other to avoid unnecessary trouble, but also guarantees and access to multiple phones, save money, very use of worth!. The soldeing should be made correspondingly, as line access L + / L-,  L1/L2 and the L1 ‘/ L2’ respectively.


The circuit is connected to the two telephone lines with L and L ‘. (We know that, when the phone is standby, the voltage level at  line L will be 48V DC  and at time of Ringing, there will be 75V and when the phone is at hook the telephone line voltage due to resistance, will be reduced to about 10V, and this circuit is designed on the basis of this principle.) The two lines are waiting, such as when a telephone call, AC current through the circuit so that the two machines produce ringing. The first line extension based L-hook, the line’s DC voltage in an instant breakdown D2 through R2 to BG1 SCR trigger voltage is applied to control an extremely quick turn-on when the BG1 to form a DC channel, telephone calls can be normal. Since then a lower line voltage, connected to the L ‘on the phone will not hear any sound. This is if you want to go to standby phone, picking up phones by dialing the number keys like the standby call (Note: Phone must be in the pulse dialing state), standby hear the ringing, the hook. Online phone call immediately after hanging up, the same principle. Increase the cell circuit can be extended to a number of road extension, but a maximum of no more than 10-way.

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