Re: home made home security

On Sat, 20 Sep 2008 03:32:11 -0700 (PDT), mentari <StephanusR@xxxxxxxxx>
wrote in message
<4f5dc094-dfac-42d4-8f4e-d8b91a57d0f6@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:

On Sep 20, 4:44 am, Marc_F_Hult <MFH...@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Fri, 19 Sep 2008 08:11:46 -0700 (PDT), mentari <Stephan...@xxxxxxxxx>
wrote in message

The RS485 system uses a single wire to communicate with lets say 40
ATMEL nodes which in turn monitor 8 IR, PIR, window sensors. That
would thus be 320 devices monitored effectively by a single
http://scratchpad.wikia.com/wiki/TwistedPairline.

So all 320 devices could be trivially disabled by cutting either one of
the two wires or by shorting them out anywhere in the system ? -- at the
perps' choice and convenience ;-)

Any cutting of the wire will trigger an alert because the master RS485
isn't getting back a packet from the slaves.

But *any* fault would deliver the same message: "System Broken" with no
specific information as to where, or why, or what to do about it.

You would also be able to locate the intrusion to the closest slave.

Oh? How, pray tell, would StephanusR@xxxxxxxxx actually be able to do this
without physically probing the line with (eg) a TDR or physically isolating
and testing individual segments? The only thing your "master controller"
knows is that it can't communicate with any node and when that communication
ended.

Multiple RS485 master/slave combinations can be used, meaning multiple
wires are used.

But that's not the "single ... twisted pair" that you premised your
discussion on. And if you use a star topology, you find yourself back at how
commercial systems are designed.

(FWIW, I have a Comtrol DeviceMaster RTS Ethernet-to-Serial with 32
individual RS-xxx ports individually configurable as RS-232, RS422 or RS-485
that is excess to my needs that I will sell for 1/3 of the new price. Each
RS-xxx port can be assigned to any computer on the TCP/IP network so one can
provide for failover or assignment-sharing of controllers) See
http://www.comtrol.com/products/family/dmrts )

You can reduce vulnerability by using a star topology but that involves
more electronics. Take a gander at DMX512a if you haven't already
recognizing that DMX can be used for both sending and receiving data
although send-only systems are by far the most popular/widespread.


Building our own RS485 circuits will cost very little.
http://en.wikipedia.org/wiki/DMX512-A uses RS485.

OK. May I suggest that you approach this/your project using a budget and
accounting for all costs of materials and time?

http://www.bdmicro.com Round robin protocol is another - there are
many ways of implementing this.

Yes, Brian Dean makes and sells some neat stuff. FWIW, I have two
1st-generation BDMicro Mavric Mega AVR boards that are excess to my needs.
Email if interested.

And yes, the issues have been addressed and dealt with many times by many
folks over many years. Which part(s) did you plan to re-invent?

The individual IC's are cheap and they don't have to be surface
mounted. Get somebody with a soldering iron to manually assemble it if
auto assembly is to expensive.

My suggestion is that either you develop the skills yourself or give up on
this approach now. (You seem to place negligible cost and value of the
"soldering" of others -- and assume that construction is a trivial exercise.
If you pay to have someone "solder" and the device doesn't work. What do you
do next? ( FWIW, I've spent *much* more time trouble-shooting DIY gear than
actual "soldering".)

Here is the schematic and PCB layout for a 4-input analog conditioning buffer
with 1-wire support that I developed. It is part of a distributed HA system
for gathering local data on temperature, humidity, occupancy and light
(THOL). What do you think it would take cost-wise to have someone else
build/solder/test this for you?

www.econtrol.org/diy_projects.htm
www.econtrol.org/4-inputbufferwith1wire.htm

Use the
http://www.smarthome.com/80380/Sony-Programmable-LCD-Touchscreen-Remote-RMAX4000/p.aspx
to interface to the RS485 master circuit.

You do understand that the "master circuit" in this case needs to be a PC,
right? And that you would have to write a custom program from scratch to
interface with your custom network? In what programming languages are you
proficient? What is the value of your time spent programming that you would
add to your budget. Or would you pay someone else?

PCB's which implement http://en.wikipedia.org/wiki/DMX512-A can be
reverse engineered by http://www.bomarc.org.

From where is your apparent fascination with "reverse engineering" derived?
There is precious little to "reverse engineer" because DMX is an
international and USITT standard. And there is much well-documented
homebrew/DIY DMX hardware.

I have some dated but still useful DMX512 references at
www.econtrol.org/dmx512.htm

There is no need to for home security automation to cost thousands of
dollars.

Home security automation systems _don't_ cost thousands of dollars if you
install them yourself.

But, even if you value your time at only burger-flipping rates, the home-brew
system you seem to be proposing _will_ (IME) cost you thousands of dollars
for a system that is less robust and valuable than if you buy an existing
product or system.

I note that you ( StephanusR@xxxxxxxxx) didn't answer my question about the
three moderately-priced, DIY, existing systems dating back a decade that can
do what you assert no existing system can do.

You might also want to have a look at Elk's Magic Module Series ( MM443 and
MM443s etc) because they are very close to what you propose.

http://www.elkproducts.com/products/elk-mm443.htm

These are self-contained, PIC-based (not ATMEL AVR) modules with four analog
inputs, four relays, timers, X-10 and I-button etc interfaces. Up to 32
modules can be linked together on a single daisy-chain RS-485 network with a
single RS-232-->RS-485 converter for connecting with a PC. FWIW, I have
about six MM443s modules, as well as speech modules, iButton interfaces, and
Cyberhouse PC home automation software that I'd sell for about 20 cents on
the dollar. If you give up on the homebrew approach you can add a (eg) NAPCO
security system that CyberHouse software natively supports. (this was my
approach). Email if interested.

Or take a _long_ look at the Elk M1G and the widespread support it enjoys in
HA control programs such as HomeSeer, Charmed Quark, Premise Systems and
others.

HTH ... Marc

Visit my ongoing Home Automation and Electronics Internet Porch Sale at
www.ECOntrol.org/porch_sale.htm

Marc_F_Hult
www.ECOntrol.org
.