Re: home made home security

On Wed, 24 Sep 2008 17:44:40 -0400, "Robert L Bass"
<Sales@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<veydnU6MM5nxKEfVnZ2dnUVZ_gednZ2d@xxxxxxxxxxxx>:

"mentari" wrote:

I wonder if you understand the technical specs on this, DMX512 and
Roundrobbin are protocols implemented over RS485 the physical layer,
you still need to grasp RS485 no matter what protocol you use.

I'd say Marc is the most authoritative person in this newsgroup when it
comes to DMX-512. He has designed and build his own DMX-512 dimming
systems. I'm probably second in experience with the stuff since I've done
a fair amount of theatrical lighting systems using DMX-512 and other
protocols.

And Robert also knows a thing or two about security systems that use RS-485
;-)

The use of RS-485 in home security and automation devices is widespread, but
where robustness is required, full-duplex is preferred -- not 1/2 duplex as
mentari has espoused/proposed. One of the reasons that USITT explicitly
states that DMX512 "is not an appropriate control protocol for hazardous
applications" is because as typically implemented, DMX is one-way only (from
controller to one or more receivers).

In my HA system there are three subsystems that use full duplex RS-485 (Elk
M1G, Aprilaire, Napco.) and two that use half-duplex (Elk MM443s and Ivie
audio auto-mixers). And then there's DMX which as typically implemented, uses
half of a full duplex -- which is not the same as "half-duplex" ;-)

When Elk developed the M1G, it switched from the half-duplex (one twisted
pair) bus used by the older MM443 Magic Modules bus to a full duplex (two
twisted pairs). Aprilaire thermostats (which wholly adopted the long-standing
Enerzone/Statnet protocol) use full duplex. Napco Gemini uses a full duplex
bus for communicating between keypads, extension modules and the main panel.

Speaking of which ;-, could you email me a copy of the install docs for the
Napco 2WAY-UNIVKIT 2-Way LCD wireless keyfob kit that I purchased from you a
while back? It can apparently connect to several different security systems,
not just Napco. My paper copy seems to have grown legs and I can't locate an
electronic copy on the web.

TIA ! Marc

Marc_F_Hult
www.ECOntrol.org
.

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