Privacy Telephone Intercom

Posted on Feb 5, 2014

The circuit you are about to see is the culmination of some effort at improving the basic Link intercom design. You may think that pulse dialing is `old hat` nowadays, but the exercise of building and testing the Link `P` in this format, and understanding how it all works, is well worth the effort. Not to mention all those out there who have the old

Privacy Telephone Intercom
Click here to download the full size of the above Circuit.

style rotary dial phones as collectables - you can now make them work for you, or display them actually working with confidence. Counting, pulsing, timing and simple logic circuits are at the heart of this design, as with all other `Link` versions. In a day where PIC controllers are popping up in electronics magazines by the dozen (about half the projects in some magazines now contain a PIC chipset, ) I feel that we could be losing the art of designing in simple `hard wired` logic, and thus this approach is used partly for educational purposes. Many readers who may decide to build up the Link `P` will `see the logic` (pardon the pun) after they have a working model servicing their home, small workshop, factory, preschool or other application. Besides, there`s an easy upgrade to Tone Dialing if you really want it anyway. Happy switching! AH Downunder. This version of the Link goes beyond anything previously attempted by me in the area of telephone type projects. Having achieved genuine ring trip (not that hard, but a bit tricky to design with `off the shelf` $5 components first time around. ) I`m now heading down the track for `two calls at the same time (either two internal calls, or one internal and one external on the outside line - providing it`s legal in your state/country of origin. ) but several things have to be achieved first. In order to achieve a status between two levels of switching for two calls at the same...

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