Re: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector

["Sean T. Stevenson" <cast55@telus.net>]

With regard to the proposal, if this is indeed intended to be a standard 
connection for communications devices, I suggest that it is not 
sufficient to describe a physical connection without also describing a 
proposed standard pin assignment and operating voltage.  Your proposal 
makes specific reference to diver units made by OTS and Divelink, 
indicating that these units operate in a two-wire mode.  Two-wire (push 
to talk, or PTT) units are common in low-cost devices, but most 
commercial diver communications setups are four-wire (round-robin, or 
open-circuit), both for reasons of improved safety, hands-free 
operation, and natural communication flow without necessitating radio 
protocol interjections in the conversation.  The proposed application 
combining comms and hydrophone is functionally identical to implementing 
communications in the four-wire mode - namely, a transmit circuit 
(hardwire umbilical to diver earphones, ultrasonic transducer for diver 
or sub-to-sub wireless, submersible speaker, etc.), and a receive 
circuit (hardwire umbilical from diver microphone, ultrasonic receiver 
for diver or sub mounted transmitter, hydrophone, etc.)

As such, any proposed standard should accommodate both two-wire and 
four-wire communications implementations, but should standardize the pin 
assignments explicitly for that purpose.  Additionally, where you 
propose that the standard connector be implemented for communications in 
two-wire mode, thus making available the other two pins for auxiliary 
devices, my immediate reaction is that this practice should be avoided, 
if for no other reason than it then becomes a standard which isn't.  
More pragmatically, you must ensure that any voltage or current present 
at these auxiliary pins remains compatible with any possible four-wire 
system which may be connected to it (in keeping with the spirit of the 
standard design), even if the operative equipment within the sub is PTT.

This raises the question of whether we should standardize on four-wire 
open communications systems (or four-wire implementation, even if the 
operating equipment is PTT), since this avoids entirely the possibility 
of lost communication due to transmit/receive timing - not a huge issue 
with a single communicating party familiar with radio procedure, but 
arguably necessary in the presence of multiple parties communicating on 
the same frequency.  In the case of through-water comms (ultrasonic), 
this theoretically opens the door to a natural conversational 
environment between several submerged subs, which I hazard a guess would 
appeal to many in the community.

-Sean




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