[asterisk-users] RS485 Audio device

Tim S tim.strommen at gmail.com
Wed Nov 2 16:31:37 CDT 2016

Before walking down this path, take a moment to think critically: How far
away is the AoR from the attendant station?  Does there need to be local
rescue/fire service access to the communications?  How reliable does the
link need to be?  Will power always be available when the AoR pone is
required to function?

I did a 27mA powered intercom system at a chemical plant a bit over decade
ago, the old analog circuits are dead simple - just a battery (or a double
battery-backed power supply in my case), a current regulator and an audio
bypass cap to make a simple audio loop.

If that's too much hardware, there are still sound-powered phones produced
- very common in mining and maritime.  An SIP phone can be wired into a
sound powered phone circuit, where the preferred usage would be talking via
SIP phone, but if all powered failed the sound-powered devices on the line
would still make a complete audio circuit.

Just a thought...


On Wed, Nov 2, 2016 at 1:30 PM, Sylvain Rochet <gradator at gradator.net>

> Hi,
> On Wed, Nov 02, 2016 at 04:21:07PM -0400, Eric Wieling wrote:
> > If cable can be pulled , you have a couple of options.
> >
> > Long Reach Ethernet from Cisco is rated for 5,000 feet. Multi-mode fiber
> > with fiber/ethernet media converters on each end would work and
> electrically
> > isolate the two ends of the cable. Both are way overkill from a capacity
> > standpoint, but sometimes there's nothing wrong with overkill. Put an
> ATA on
> > the far side.
> We are using Westermo products for this case. Westermo DDW-120 is rated
> up to 15 km (@ 192 kbit/s), higher speed is indeed achieved for shorter
> lengths.
> It's not cheap, but it works well, even in harsh industrial
> environments.
> Sylvain
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