Dual audio decoding electronic circuit design

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DTMF (Dual Tone MulTI Frequency) dual-tone multi-frequency signal decoding circuit is an integrated circuit widely used in push-button telephones (fixed telephones, mobile phones), program-controlled switches and wireless communication devices. It includes a DTMF transmitter and a DTMF receiver. The former is mainly used as a dual-tone signal transmitter for a push-button telephone, and transmits a set of dual-tone multi-frequency signals to implement audio dialing. The dual-tone multi-frequency signal is a set of combined signals composed of high-frequency signals and low-frequency signals. CCITT and China's national standards both stipulate the correspondence between telephone keyboard keys and dual-tone multi-frequency signals. The telephone remote control system uses MITEL. The MT8870 DTMF receiver is produced as the decoding core of the DTMF signal. MT8870 is mainly used in program-controlled switches, remote control, wireless communication and broadcasting systems to realize the separation filtering and decoding function of DTMF signals, and output four-bit parallel binary codes corresponding to 16 kinds of frequency combinations. MT8870 has dial tone suppression and analog signal input adjustable function, so when designing MT8870 DTMF decoding circuit, only need to add some RC components.

Dual audio decoding electronic circuit design

The dual-tone multi-frequency DTMF signal decoding circuit of this system is mainly undertaken by MT8870. The connection of MT8870 is as shown in the figure. Its 2 and 3 feet receive the dual-tone multi-frequency pulse signal from the telephone. The dual-tone multi-frequency signal passes through its internal dial tone filter to filter out the dial tone signal. The preamplifier is sent to the dual audio filter, and the dual audio signal is separated by the high and low audio signals, and then sent to the output decoding circuit through the high and low group filters, and after the digital operation, in the data The output (11 to 14 feet) outputs the corresponding 8421 code. The data output terminal Q4~Q1 of MT8870 is connected to the single-chip microcomputer, and the single-chip microcomputer recognizes the 4-bit code. The telephone button and the corresponding decoding (Q4 ~ Q1) output. R/P, REDIAL, HOLD, HANDSFREE and other functions are used. In order to make the MCU obtain valid data in time, the CLD valid terminal of MT8870 is connected to the INT0 pin of the CPU after being inverted. When the MT8870 obtains a valid dual-tone multi-frequency signal, the CLD level changes from low to high, and then reverses to low. After the CPU detects, the input port receives a valid binary code. Invalid dual audio signals (telephone line noise, people's voice signals, etc.) will not cause the CLD end of the MT8870 to change. The peripheral circuit of the DTMF receiver is shown in the figure.

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Circular Connectors
Circular connectors, also called [circular interconnects," are cylindrical, multi-pin electrical connectors. These devices contain contacts that transmit both data and power. Cannon (now ITT Tech Solutions) introduced circular connectors in the 1930s for applications in military aircraft manufacturing. Today, you can find these connectors in medical devices and other environments where reliability is essential.
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Types of Circular Connectors

Circular connectors typically feature a plastic or metal shell surrounding the contacts, which are embedded in insulating material to maintain their alignment. These terminals usually pair with a cable, and this construction makes them especially resistant to environmental interference and accidental decoupling.


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