Using a combination of two simple circuits, you can make the phone played a simple motif identification - this can be "Smoke in your eyes", if you are a developer of electronic circuits, while the Professor, perhaps more like "Gaudeamus igitur", and the journalist will prefer "somewhere over the rainbow".
Number of programmable motives rather large. Here are the pairing scheme, which allows to connect these two circuits, previously published in the journal "electronics".
Input Schmitt trigger IC 74121-sinusoidal output signal generator call generates short pulses with steep fronts. Output negative pulses of the generator with one stable state trigger synchronizer - IP type 555, which generates a strobe pulse with a duration of about 10 s, allowing the passage of the entire cycle of musical generator call. This cycle will repeat until, while not lifted the handset of the called phone or put the handset of the calling phone.
(click to enlarge)
It may be that on some telephone station frequency ringing current is not equal to 40 Hz. In telephone lines are used to call frequencies of 20, 30, 42, 54 and 66 Hz, and in a PBX installed in buildings, the frequency of the calling tone is usually equal to 30 Hz.
This scheme can work with any of the frequencies of the call.
The musical idea of a phone call may seem a bit frivolous. Musical challenge was used as an entertainment effect in one of the old radio dramas. However, this scheme may be adapted to control not only the telephone call, but also other devices.
And one more thing - before you install the schema of musical challenge, you should consult with the telephone exchange, despite the fact that the optocoupler and does not create much of a load on the line. In some cases, a telephone station sets the musical call devices, but they reproduce only three notes, i.e. nothing like the motif.
Author: N. Dugan; Publication: N. Bolshakov, rf.atnn.ru