Elk M1DBH Data Hub Question

[dBeau]

I've read the docs a couple of times and am still having trouble getting my mind around how to use two M1DBH. The instructions are pretty clear when it comes to doing home runs from all devices, however, I'd like to have two "homes". The first is at the panel itself and the second is out in the garage where I plan to put a second can to hold a couple of input and output boards. The idea is to keep the wire runs down by putting the boards near where they will be used. This means that the two hubs will only have four or five devices each. The docs assume the first hub will be filled up with J9 going to J1 on the next.

So, what to do if the first hub is not filled up? I'd really like to have only one cat5 running between the two cans. Suggestions on how to power the devices in the other can would be helpful too. I'd guess that the cat5 can carry enough current for a few devices, but what if I need more?

Thanks!

 

[DeLicious]

i don't think there's really any reason that you have to go from J9 to J1 on the next. i think the instructions assume that you would only need the second one if you filled up the first one, but there's no reason you couldn't go from J5 to J1 as long as J5 was the last one used on the first board. somebody correct me if i'm wrong.

 

[Steve]

You should be able to hook both M1DBH to the M1 directly, put one local and 1 in the garage. Pull the terminator off the M1, fill the DBH in panel until where you want and plug in terminator plug and do same in garage. That should give you properly terminated bus. You can always put a meter on to double check.

 

[dBeau]

You should be able to hook both M1DBH to the M1 directly, put one local and 1 in the garage. Pull the terminator off the M1, fill the DBH in panel until where you want and plug in terminator plug and do same in garage. That should give you properly terminated bus. You can always put a meter on to double check.

The docs give the impression that there is some value in daisy chaining all of the devices. Connecting both hubs to the M1 would mean there are two "chains" instead of just one. But, it does also state that there should be no more than two terminating resistors on the bus, so that seems to imply what you are suggesting would work too.

It just occured to me that to keep a single "chain", I could plug the cat5 to the second hub into the first ununsed jack of the first hub (inplace of the terminating resistor). Then at the second hub, I could connect to the screw terminals instead of terminating with an RJ45 into J1. The trick would be to ignore the "return" wires (grn/wht A1 and wht/grn B1) when making the connection. Then, wire to and terminate the second hub as shown in the instructions. If my thinking is correct, this should result in a single "chain" with one terminating resistor.

...but my head is still itchy and needs more scratching.

 

[gcimmino]

I'd second Steve's approach. In fact, that's how I have my M1 setup. One DBH in the main building and the other in the building next door.

One run from each DBH to the M1, terminate the DBH's, remove termination on M1.

In effect, you still have a single bus, now the M1 is logically in the middle of the bus.

 

[dBeau]

I'd second Steve's approach. In fact, that's how I have my M1 setup. One DBH in the main building and the other in the building next door.

One run from each DBH to the M1, terminate the DBH's, remove termination on M1.

In effect, you still have a single bus, now the M1 is logically in the middle of the bus.

Ah... putting the M1 in the middle of the bus makes it easy to think about. I can go back to scratching my head if I need to add a third

 

[Steve]

Yea, a third would change things a bit. You would have to chain that one off of one of the others. Just remember it is 1 bus where each 'end' is terminated. If you had 1 you would put the terminator on the M1 itself and that would be 1 end and the end of the chain on the DBH the other end. As already said, this way is still one bus with the end of each DBH chain an end to the bus and the M1 in the middle. As long as you remember the golden rule of only 2 terminators, 1 at each end you will be fine.