This is a simple device that splits a single ClearCom or similar intercom
line into two separate audio channels, sharing a single power supply. It
creates a new audio termination point for the second "universe" to allow
independent conversations, and maintains functionality of the CALL light.
It implements the circuit shown near the end of this document that explores how such systems work, and the particulars of the termination circuit are corroborated by ClearCom's own documentation (PDF). I've been meaning to build one of these for years, and never got around to it until faced with the possibility of needing two channels on an event where only a single-channel base station was going to be supplied. [Click on small pictures for larger copies.] |
The right answer was to load up my largest punch and die, and rough out most of the area in the form of many overlapping holes. |
Next problem was to continue out to my nice round scribed boundaries; the template for drawing same is also shown here. |
The termination circuit went in with totally old-school wiring technique. Pins 1 and 2 straight through; pin 3 is where the magic happens. |
Done! The label wound up a little wonky, but it's good enough for the purpose. |
A couple of years later, after the specific set of intercom gear I
was most familiar with had all
fallen under my care
anyway, I added a channel-join switch to this widget. Again, a
simple enough thing -- for the third connector's pin 3, either connect
to the terminator or the pin 3 bus of the other two.
An additional label was added to the front documenting this, and advising "switch briskly!" as moving the switch slowly would leave the new channel's bus completely unterminated for just a moment. An open mic anywhere downstream of that could easily cause brain-destroying feedback until the internal rocker of the switch could contact one or the other side. I didn't have any make-before-break switches in stock, as they're a somewhat specialty item which would nonetheless be the correct answer for this. |