ELK M1RB and RS-485 data bus

I want to have a remote building set up as a separate area on my M1G. The cat5e wire between the M1G/M1DBH and the remote building has a potential exposure via a pull box on the outside wall. In a different thread, someone mentioned that if an intruder was able to get to the data bus wire, he could put a high voltage to it and possibly damage/cripple/destroy the M1G. That led to a suggestion to put a tamper switch on the pull box cover, which I will do.

If I want to go one step further to protect the system and my home, can I run the eight conductors in the data bus cat5e wire thru an M1RB relay module (one conductor per relay) ahead of the M1DBH data bus hub? That way, if an alarm was set off by the tamper switch or the wires being cut outside the house, the M1G could open the eight relays, effectively isolating the outside data bus wire from the M1G in my home. I guess the big question is can the data bus reliably communicate "thru" the relays? The total length of the data bus wire run is a little less than 200'.

One other question...the diagrams in the Elk manuals always show a single keypad/board/etc. at the end of a run to the M1DBH. Can multiple keypads/boards be daisy-chained on a single run from the M1DBH? In other words, can I have a single cat5e running from the M1DBH to my remote building that serves a couple of keypads and a few expansion boards in the remote building? If so, does the last device on the line need to be terminated, or does the M1DBH handle the termination in this scenario, too?

Thanks,
Ira

Yes you can put multiple modules on a data bus run from a M1DBH. Make sure you keep the data bus, data A and data B wired in series, not parallel.

The data bus on the M1 has over voltage clamps to about 6 volts on its data lines. Every data bus out there has its limits of over voltage protection. A 1/4 amp fuse inline with the data bus will also give protection. The overvoltage clamps will cause the fuse to blow if an overvoltage is applied.

There should be no problem with the data bus working through relays contacts.

I know this is a little off topic, but you seem to be putting a lot of work into an area that I doubt few professional thieves will care about. From the research I've done, most pros will cut the phone line, use a cell phone jammer(easy to buy online), and try to spray something in any outdoor siren they can find(often with a pole). Then they kick down the most secluded door or window, run through the house, and are gone in a few minutes. Only time I've seen a story of trying to zap an alarm is using a taser on a keypad, not sure if it was successful. My 2 cents is that security systems are not going to deter someone that sophisticated, you probably need a security guard, dog, watchful neighbors or more layered defences.

Anytime you run wires outside you risk damage from spikes/surges and ground loops. Ethernet is transformer isolated.

You could consider isolating the RS485 or converting to fiber. Search for B & B electronics for possible converters. I had to do this with RS232 that controlled an X-ray set.

Does Elk support Fiber conversion on the data bus? I know wireless converters don't work.

icellama21 said:

I know this is a little off topic, but you seem to be putting a lot of work into an area that I doubt few professional thieves will care about. From the research I've done, most pros will cut the phone line, use a cell phone jammer(easy to buy online), and try to spray something in any outdoor siren they can find(often with a pole). Then they kick down the most secluded door or window, run through the house, and are gone in a few minutes. Only time I've seen a story of trying to zap an alarm is using a taser on a keypad, not sure if it was successful. My 2 cents is that security systems are not going to deter someone that sophisticated, you probably need a security guard, dog, watchful neighbors or more layered defences.

Click to expand...

I think all of us are guilty of going overboard at some point when designing/implementing DIY HA/security. It's the nature of the beast. Someone else brought up the possibilty of damaging the Elk in this manner, and I thought it made sense. If I can defend against such a threat for under $100 and an hour of labor, I will probably do so.

With that said, if KISS's idea of using fiber optics to electrically isolate the bus wire will work with the M1G data bus, I will definitely consider that as an option (maybe do both). As I said on another thread I started, surge protection is a big issue for me. I've had equipment damaged by one lightning strike. Fortunately all it did was take out a DirecTV DVR.

How about it Spanky? Are you still there? Will the M1G data bus hub tolerate a few feet of fiber optic cable and the associated RS-485 converters in the run?

Ira

I can't post URL's yet easily, without help because of my newbie status.

Can you give me some quick stat's about the Elk's 485 bus or tell be where to look?

Particularly baud rate, levels and whether hardware or software flow is used?

Fiber, inherently isolates.

What happens in a storm is that the Earth charges. This can create a potenial difference on the order of volts which can take out a lot of logic stuff. Rs485 does a lot in eliminate ground loops, but won't do anything if the ground potential raises.

We had a computer center that was about 300' x 300'. It took out a few switches whose wires just went from one side of the building to the other. That section of the backbone was replaced with fiber.

I think, that isolation alone will run about $125 if memory serves me correctly.

KeepItSimpleStupid said:

I can't post URL's yet easily, without help because of my newbie status.

Can you give me some quick stat's about the Elk's 485 bus or tell be where to look?

Particularly baud rate, levels and whether hardware or software flow is used?

Fiber, inherently isolates.

What happens in a storm is that the Earth charges. This can create a potenial difference on the order of volts which can take out a lot of logic stuff. Rs485 does a lot in eliminate ground loops, but won't do anything if the ground potential raises.

We had a computer center that was about 300' x 300'. It took out a few switches whose wires just went from one side of the building to the other. That section of the backbone was replaced with fiber.

I think, that isolation alone will run about $125 if memory serves me correctly.

Click to expand...

Here is a link to the Elk data bus hub. I, and probably most people, use it to simplify the data bus wiring. There is a link to the product manual on that web page. One end of the cat5e/RS-485 cable plugs into it. The other end is wired into into one or more expander boards like these. Isolating the remote end (the one with the expanders) may be more expensive than the expanders themselves, depending on what all is on the remote end. I'm not sure if the way the data bus is wired up will work with what B&B offers.

I was looking at the B&B website. Some interesting stuff if one is willing to pay that much. It may be worth using fiber to isolate an ethernet cable I have running in the same conduit out to the remote building. Is there anything similar for a telephone connection, or is that even possible? I assume you only need a couple of feet of fiber to provide protection, right?

Ira

Elk is looking at a fiber solution for the M1.

Currently the data turn around time from transmit to receive of 4ms is to short for the fiber systems tested.

I bet you could use a couple of embedded linux devices at each end with RS-485 ports and fiber transceivers, and then use "socat" to create a bi-directional pipe from RS-485 to IP. Try it with TCP first. If that works, socat supports SSL and you can try switching to that. If it doesn't work, try UDP.

Side A: socat /dev/<rs485 dongle>,raw,b<bitrate of rs485 bus> TCP:<ip of side B>:31337
Side B: socat /dev/<rs485 dongle>,raw,b<bitrate of rs485 bus> TCP-LISTEN:31337

You can put one of these running Ubuntu off a USB stick at each end:
http://www.newegg.com/Product/Product.aspx...N82E16813121342

With one of these on each one:
http://www.southernhillscomputer.com/usbtorscorj.html

And this for fiber:
http://www.sourcingmap.com/fast-ethernet-f...00-p-35776.html

Or, you could probably even use 802.11 wireless to get away without using any cables. Then again, who knows if this would work at all. If someone wants to get me the equipment, I'll have an answer within a day after getting the stuff.

I have always wanted to try these:

http://dataprobe.com/ipio8-web-relay-control.html

One of those fiber converters goes to about 155,000 baud with a 6 uS turn around time. That's probably pretty fast.

No idea what the baud rate is for the Elk. I read that it's software control for direction and full duplex.

Elk bus is 38,400 baud, half duplex.

Anyone with more information on fast turn around time (transmit to receive) on fiber transceivers, let me know.

Spanky said:

Elk bus is 38,400 baud, half duplex.

Anyone with more information on fast turn around time (transmit to receive) on fiber transceivers, let me know.

Click to expand...

How about: http://www.bb-elec.com/bb-elec/literature/2814x_ds.pdf

These say network pulse duration <1µs:

http://www.gesecurity.com/portal/GESDownlo...pe=Data%20Sheet

I have used them with success for access control panel communication successfully at 9600, 19200, and 38400 baud.