Wiring for ADICON Modules and TEMP08 Wiring

[Jim Doolittle]

In preparation to automate my pool shed, I want to run wires from house to the pool shed (about 150 foot total). I want to connect 1 or 2 Secu16 units as well as a one wire network extension for a TEMP08.

If I do this I will be set to control swimming pool, watering of garden, floodlights, etc.

I have discussed burying a line and use of PVC but I am wondering if anyone sees a problem with my recent plan which would involve a lot less effort.

There is a phone line going about 75 feet from house to the pool. I am not sure what you call the wiring but it is a four wire phone line covered with grease and encased within a black sheath. I would like to extend that wiring to the pool shed and connect up more ADICON modules (Secu16) and add some one-wire sensors.

So, here are my questions:
<UL TYPE=SQUARE>
<LI>Will the wiring be OK for the application I describe?
<LI>If so, how should I splice the existing wire so that it remains watertight?
<LI>I would like to run the line extension alongside the pool fence as this would ensure that the line is more protected however I have wiring for Malibu lights that I do not want to interfere with the wiring for the ADICON/TEMP08. Is there a potential problem here?[/list]

[rocco]

Jim:
First, I make assumptions (not having an Ocelot, myself).
1) You are using the RS485 lines (2 wires) to connect your Secu16.
2) That the phone cable you describe is CAT3.

If 1 and 2 are correct, you should have no trouble with the Secu16s, as long as you use a twisted pair for the RS485. I don't have much experience with one-wire, but my gut feel is that it should work.

I would make the splice water tight by greasing it up and then shrink-wrapping it. The RS485 will be impervious to the Malibu lights, but I don't know about the one-wire.

[Jim Doolittle]

RS485 is correct for ADICON Ocelot. And it does look like the wire is CAT3 after I looked up what CAT3 wire would look like.

So, other than a trip to get some CAT3, it looks like I am set and even if I only get one of the two work, I will be happy. I wanted one-wire to use cheap temperature sensors but if I can only get the ADICON to work, I could use a more expensive temperature sensor (they call it a "bobcat") with it.

Thanks,

[smee]

Jim:

I assume your cable has 2 twisted pairs. For the RS485, you'll need 1 twisted pair and 1 ground (total of 3 wires). 1-wire needs 1 twisted pair for parasitic sensors (1 wire for data, 1 for ground).

If the wire has 2 twisted pairs, you could try running a common ground for both the rs485 and 1-wire. I'm not terribly thrilled about that (connecting the grounds of your Ocelot and TEMP08 together) but it might work. You may have problems with grounds being at different levels. I think you'll also increase the risk of damaging multiple pieces of equipment during things like lightning strikes.

I run rs485 and 1-wire through a single cat5 cable, but they are completely separate (not sharing the ground or any other lines).

[jon00]

Jim,

I had a temporary run of telephone cable with the exact same set-up as you have described (about 60ft) and it worked fine apart from the problems I had registering the SECU16 with the Ocelot due to different power supplies after a loss of power.

I finally changed the cable set-up so that both power & RS485 were supplied to the Ocelot via a new length of cable and left the 1-wire on the telephone cable.

smee...RS485 only requires 2 cables to work but a 3rd (ground) is useful to screen against interference!

[rocco]

You may or may not need a ground. It depends on your power, and the ADICON RS485 receivers.

RS422 and RS485 receivers only work if the voltage of the incoming signals is within a particular range of the receiver's voltage, called the Common-Mode Voltage. For most older receivers, the common-mode voltage is +/- 7 volts. For newer receivers, its +/- 15 volts. The ground wire is one way to insure that the common-mode voltage is close to zero.

The receivers I typically use can operate with a common-mode voltage of over +/- 1000 volts, so I tend to forget all about the ground wire.

If the receiving end is floating (powered by a transformer), many manufacturers keep the common-mode voltage close to zero by center-tapping the terminating resistors to ground, or by installing biasing resistors to +5volts and ground.

So we have to look at the input circuit of the Secu16 to know for sure whether the ground wire is necessary.

[Jim Doolittle]

The Ocelot and Secu$$ modules require four inputs two supply 12V power and two provide the RS485 network. There is no input for ground.

[smee]

Jim, one of the two power connections is ground, the other 12V (assuming it's a DC supply).

I believe that the RS485 standard does require a ground. However, as has been noted above, how you get that ground is pretty flexible. Using earth ground is usually ok.

I usually go ahead and throw in a ground wire. If I've got the wire available, it doesn't hurt anything. If power is being run along the same cable, it's usually there, anyway.

Rocco:

Which receivers are you using?

[jon00]

I don't wish to start an argument - call it healthy discussion

However.....

The Ocelot/SECU16 requires 9-12V AC or DC. If you take a peek inside these units you find that the two power terminals go straight through a bridge rectifier, smoothing and then to a 5V regulator. There is no earth or 0V connection via the PSU route. This is why the terminals are only marked as power. You can put the +ve of a 12V DC supply to either connector if you so wish.

The two remaining connectors are for the RS485 data which is why I stated for this set-up only two data cables are required.

It may well be that you run the Ocelot & slave modules from a single DC 12V supply and connect the screen/shield of the cable to 0V and this is what I would do. However, my point is that the system does not require a 3rd ground wire to function correctly.

[smee]

I stand corrected. Jon's right about the setup of the Ocelot. Thanks.

[rocco]

Smee, the one I use the most is an HP (Agilent now) HCPL2602. It's a combination line receiver and optocoupler, which is how it gets it's CMR. It's no good for multi-drop since it has active termination built-in. Try this ugly link:

http://we.home.agilent.com/cgi-bin/b...OUNTRY_CODE=US

For multidrop, I usually use a Maxim part, most often the MAX1485CUB.