Traditional Chinese Practical Wired paging intercom: Circuit Design, Parts List & Workshop Prototype Guide

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Wired paging intercom systemThe paging intercom system introduced in this article consists of a host computer and several auxiliary computers. The main machine can be installed in the manager's room, communication room, and hospital duty room. Each room is equipped with one auxiliary machine. Only one bus is needed to connect the main machine and all auxiliary machines. This system uses dual audio coding, so it is easy to operate and also enhances the system's anti-interference ability. If the host wants to talk to a certain auxiliary unit, just press the corresponding auxiliary unit number to connect to the auxiliary unit for intercom, while other extensions are closed.The host has a total of 16 dialing keys. This system only needs to operate the 10 keys "1~9" and "D", among which "1~9" are address keys and "D" is the reset key. The receiver is generally in a waiting state, and only the power amplifier circuit has no power supply, so the speaker produces no sound. The DTMF decoding and electronic lock circuits are always working. Once a dial number with the same address as the receiver's address is received, the electronic lock is opened and the intercom system's working power is turned on to achieve the paging and intercom function.How the host works:The working principle of the host is shown in Figure 169-1. IC1 is a dual-channel audio amplification chip integrated circuit TDA2822. Its main features are high efficiency, low power consumption, a typical static operating current of only about 6mA, and the circuit's wide adaptability to voltage (1.8~15V). IC1 amplifies the audio signal generated by the microphone and dual audio encoder. The amplified audio signal is output through pin ① and sent to the output of pin ③ to drive the speaker to produce sound, thus realizing the duplex intercom function.IC2 is the DTMF dedicated integrated block MK5087. It and other related components form a dual audio encoder. That is, when a key is pressed, a pair of dual audio signals will be generated, one of which comes from the high frequency group and the other from the low frequency group. Please refer to Table 1 for the frequency group corresponding to each key.The working principle of the auxiliary machine:The working principle of the auxiliary machine is shown in Figure 169-2. The intercom circuit composed of IC1 is the same as the host computer and will not be described in detail here. IC2 is an electronic lock composed of DTMF decoding circuit IC3 (CD4028) and IC4 (CD4043). The working power supply of the whole machine is 6V. The DTMF encoded signal sent from the host is sent to the MT8870. After being amplified by the input circuit and filtering out the noise outside the DTMF signal range, it is sent to the high and low frequency filters at the same time. After digital detection and processing, it is converted into a binary signal for output. alt="240.jpg (66497 bytes)">Figure 169-1 …

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