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RE: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector
Sean,
I am not sure that your 4-wire mode applies here. It has been a long time
but I seem to remember that the 4-wire system is a hardwired comm system
with the diver so would not apply to a free ranging sub (i.e. not on an
umbilical). All PTT equipment is housed within the hull. We are talking
about connecting a hydrophone in most cases. Depending on how you dive, two
transducer might be used...one above the hull and one below.
R/Jay
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Sean T.
Stevenson
Sent: Friday, December 18, 2009 9:31 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector
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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