Same-line telephone switching circuit (1)

Same-line telephone switching device (1) In many cases, one telephone outside line is connected to multiple telephones. Although the utilization rate is high, the confidentiality is too poor. This device can effectively solve this problem with the minimum number of components. When using the phone, the one who picks up the phone first has priority, and the one who picks up the phone second is silent; when answering the phone, both phones A and B ring at the same time, the one who picks up the phone first has priority, and the one who picks up the phone second is silent. During the call, machine A and machine B keep each other confidential. working principle    　　

Two telephones A and B are connected to an outside line L1 and L2 through relays J1 and J2. In the figure, status relays J1 and J2 are both in the released state. Therefore, both telephones A and B are connected to the outside line. When a call comes in, the ring current voltage causes both phones to ring through the coupling capacitors C1 and C2. Assuming that phone A picks up the phone first, relay J1 provides a DC path and its contacts are closed (that is, the movable contact switches from upper to lower), thus cutting off the path to phone B. If phone B picks up the phone first, similarly, the access to phone A is cut off, thereby completing the mutual confidentiality function. When using the phone, whoever picks up the phone first will occupy the outside line first, and then there will be no sound when picking up the phone. The functions of the capacitors C1 and C2 in the component selection and production circuit are to provide an exchange path for the ring current and voice; and to prevent the relay from jumping during dialing. Generally, 1000u electrolytic capacitors are used. The relay is single pole double throw (5 pins) and the coil working voltage is 9V. The entire device must distinguish the positive and negative external lines when connecting.