Musical phone call. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Musical phone call. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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Using a combination of two simple circuits, you can get the phone to play a simple identification motif - it could be "Smoke in your eyes" if you are an electronic circuit designer, while a professor might like "Guadeamus igitur" more, and a journalist prefer "Somewhere over the rainbow".

The number of programmable motives is quite large. Here is an interface diagram that allows you to connect two circuits published earlier in the journal "Electronics".

The input Schmitt trigger-IS 74121-forms short pulses with steep edges from the sinusoidal output signal of the call generator. The negative output pulses of this single steady state oscillator trigger a synchronizer, a type 555 IC, which generates a strobe pulse of about 10 seconds duration, ensuring the passage of the entire cycle of the musical call generator. This cycle will repeat until the called phone goes off-hook or the calling phone goes on-hook.

(click to enlarge)

It may turn out that at some telephone exchange the frequency of the ringing current is not equal to 40 Hz. Telephone lines use 20, 30, 42, 54, and 66 Hz to call, with indoor PBXs typically using 30 Hz.

This scheme can work with any of the specified calling frequencies.

The idea of a musical phone call may seem a bit frivolous. The musical challenge was used as an entertainment effect in one of the old radio shows. However, this scheme can be adapted to control not only a telephone call, but also other devices.

And one more circumstance - before installing a musical call scheme, you need to consult with the telephone exchange, despite the fact that the optocoupler does not create a special load on the line. In some cases, the telephone exchange itself sets up musical calling devices, but they play only three notes, that is, nothing like a motive.

Author: N. Dugen; Publication: N. Bolshakov, rf.atnn.ru

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