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About
P2Dgizmo stands for Pulse to DTMF gizmo.It is a device which teaches a Plain Old Telephone to "sing" modern DTMF.
The original ZIP-file can be downloaded here, and the author also has a demo video available on youtube
Schematics
Note: the schematics as shown below will not work on European telephone lines.because European telephone lines do a polarity switch at the end of each call.
(This might be solved with a bridge-rectifier though)
(Click on the image below to get a bigger picture)