A method, circuit, terminal and system for sending dtmf tone

Abstract

The embodiment of the present invention discloses a method, circuit, terminal and system for sending DTMF tones. The method includes: when a dual-tone multi-frequency DTMF signal is generated, amplifying the DTMF signal based on a power amplifier; The signal is input to the bus under the action of the electronic switch. In the embodiment of the present invention, when the DTMF tone communication circuit is not sending the DTMF tone, the electronic switch is in the disconnected state; When the electronic switch is disconnected, even if there is a signal on the bus, the power amplifier is open to the bus, which does not affect the bus impedance, and more pairs are built in the entire system. When talking about subsystems, it can better match the load impedance of single-channel and multi-channel subsystems at the same time.

Description

technical field [0001] The invention relates to the technical field of communication, in particular to a method, a circuit, a terminal and a system for sending DTMF tones. Background technique [0002] With the shortage of land resources, the land use rate of the real estate development is getting higher and higher, the scale is getting bigger and bigger, and the cost of materials and labor is getting higher and higher. Therefore, when considering the elevator intercom system, it is desirable to lay as few wires as possible. Therefore, many manufacturers choose to use a two-wire bus-type elevator intercom system to deal with this problem. Using dual-tone multi-frequency (DTMF) tone signal communication, it is only necessary to lay a two-wire elevator intercom system from each intercom subsystem. cables, and then lay all the cables in parallel to the monitoring center, figure 1 It shows the structure schematic diagram of the existing bus-type intercom system, and the wiring...

AI Technical Summary

Problems solved by technology

According to the characteristics of the NPN triode, in the amplification area, the resistance Rce between the C and E electrodes is relatively high, so the transmission impedance of the DTMF tone (that is, the output impedance = Rce+R2) is relatively high, that is image 3 The equivalent circuit diagram of the DTMF tone transmission shown in the figure shows that the transmission characteristics of the DTMF tone (that is, the DTMF signal) will be very different under the condition of different impedances of the bus; since the C pole of the triode is powered by the bus, in The number of channels is small, the impedance of the bus is high, and the amplitude of the DTMF tone is large, which may cause the instantaneous voltage of the bus to be too low. There are devices that are sensitive to the voltage range on the intercom system bus, and there is a risk of abnormal system operation.

Instantaneous low voltage may cause the CPU power supply of the system to be too low, resulting in system instability, which will cause the intercom device on the system to reset or other risks

[0004] Depend on Figure 1 to Figure 3 As shown in the structure, when multiple intercom subsystems are equipped, the DTMF tone signal sent by the intercom subsystem will attenuate significantly after passing through the terminal circuit, thereby affecting the communication effect; as the number of intercom subsystems is gradually increased, The dynamic range of the load impedance on the bus fluctuates greatly, and the impedance of the DTMF tone sending end (that is, the output impedance) is difficult to match the single-channel and multi-channel load impedance at the same time; when multiple intercom subsystems are mounted on the bus for DTMF tone communication , during this process, the impedance of the entire sending end (output impedance) is relatively large. As the number of intercom subsystems on the bus increases, the amplitude of the DTMF tone at both ends of the load will gradually decrease, resulting in a decrease in the reliability of the DTMF tone communication. Matching the load impedance of single-channel and multi-channel subsystems, the number of elevator intercom subsystems carried will be limited compared to the DTMF tone transmission scheme of the present invention. It is precisely because of the above reasons that the carrying capacity of the bus-type elevator intercom system is limited. That is, the capacity of the elevator intercom subsystem accessible on the bus is limited

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