Question: How can a single-chip microcomputer detect when a telephone is hung up?

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Question: How can a single-chip microcomputer detect when a telephone is hung up? [Copy link]

When a call ends, the caller or the called party hangs up, and the switch sends a busy signal to the other party. After a period of time, the busy signal needs to be cancelled. How can I use a single-chip microcomputer to detect whether the phone is hung up?

789

Correction: it should be called "hang-up tone":). In this case, to distinguish between the urging tone and voice, the urging tone can be processed as an intermittent sine wave through the circuit, and the number of pulses can be counted to detect whether there is a urging tone. However, the same circuit can also convert the voice into a similar sine wave (observed with an oscilloscope). At this time, by counting the number of pulses, it is impossible to determine whether it is a urging tone or a voice. The CP mode of MT8888 can directly demodulate the signal tone, which can also be achieved with LM567. The signal tone has an obvious pattern.

Joy

[:)] I learned something new, good

njdyp

Could you please introduce the basic characteristic parameters of telephone signaling signals including dial tone, "hang up" tone, "busy tone, etc. Such as the frequency of the single tone used, the on-off interval, etc. Let us enrich our knowledge.

maningmei

LM567。。。。。