OmniPro II - multiple zones sharing a ground?

[2MuchTech]

I've got a new device I'm trying to hook up to my OmniPro II system, and it has 4 separate outputs (they correspond to 4 individual channels that get triggered on the device).  The problem is that while it has a separate wire for each output, it has only a single shared ground/common.  Will the OmniPro handle chaining the "-" side of four different zones together?  When I measure the impedance between the "-" side of two different unused zones on my system, I get ~5 k ohms, so clearly they aren't all tied directly together in the OmniPro panel.  The only way (other than a messy 4 relay interface between the device and my OmniPro) I see of hooking up more than one channel from my new device is to daisy chain the common wire from the device to 4 different OmniPro "-" connections on 4 zones.

 

[ano]

So question for you, is the common ground also connected to the power terminal of your device (I'm assuming negative) and is it powered from the Omni power supply? Are you using EOL resistors on other zones?

 

[2MuchTech]

I'm using my OmniPro (actually a Leviton aux 12v power supply in the enclosure with the OmniPro) to provide power to the new device. I will have to check impedance between the common output and the negative power lead, but I assume it's the same electrical circuit even though it's a separate connector on the board.

And yes, I am using EOL resistors on my existing OmniPro zones. I had envisioned daisy chaining 4 "-" connections together and installing an EOL resistor on each of the positive contacts coming from the new device.

 

[ano]

If the device ground is isolated from the zone common, it should work.  I'm less hopeful if the zone common is also connected to the negative, but it still may work. Omni zones have really two parts. Each zone has a constant current source, and a rudimentary voltage meter.  From your Physics 101 days you may have learned that resistance is voltage/current.  With a fixed current, the resistance can be measured by reading the voltage.  The Omni voltmeter is a simple 8-bit A-to-D design created many years ago, so its simple.  With PC Access you can even see the voltage its reading. There is a voltmeter for each zone, and I believe the - terminals float. 
 
So I believe what you are trying to do should work.  If the zones are used for security, really test it out first.

 

[2MuchTech]

Well, it's not working, but I don't think it has anything to do with me chaining multiple zones' "-" terminal together.  It looks like the device I'm trying to connect uses some type of solid state relay on its outputs, and that's not compatible with the OmniPro.  Even if I just connect a single channel from my new device to a single zone on the OmniPro, the zone never shows "Secure".  So unless there's a way to do something with a diode to block whatever current is feeding into the OmniPro zone, I suspect I'm going to have to resort to driving physical relays with my new device and have the relay outputs connected to my OmniPro zones.
 
See below for a copy of the wiring examples they provide.  Since my OmniPro is set up with normally closed sensors and EOL resistors in series (instead of parallel as this diagram for my new device shows), I already tried changing the new device to its normally closed mode.  Regardless of which way I connect it the OmniPro isn't seeing the correct resistance on the line and it doesn't go to Secure.
 
[sharedmedia=gallery:images:937]

 

[ano]

Actually i wondered about that. An open collector output or a relay output would probably work, but keep in mind that zone current is pretty low so may not work with switches that require a higher current. You could probably go with some reed relays which are pretty cheap and should be easy.

 

[JonW]

Most solid state relays work by having a leakage current going through them.  You would need a mechanical relay for this.  I've found that reed relays often work for these types of things as they use very low current to drive them (unlike normal relay coil voltage).

 

[2MuchTech]

I found a nice 12 volt 16 relay board at my local MicroCenter, and everything seems to be working now.  The relay board is a SainSmart board, so not exactly security rated, but at $21 the price was right, and it even has optically isolated circuits, so I won't have to worry about any inductive feedback from the relays.  At the current time my application for this isn't truly security, so I'm okay using relays that aren't rated. The only downside I've found so far with this board is that the trigger inputs are brought out on a dual row berg header, so it's not going to look as nice as it would have with screw terminal blocks.  But it will probably look better than a bunch of individual reed relays, even if the reed relays are more appropriately sized for this low current application.  If I remember, I'll post pics later in case anyone else has an application that requires this type of relay "buffer".

 

[2MuchTech]

Here's a picture of the SainSmart relay board I'm using with my OP II.
 
[sharedmedia=gallery:images:947]

 

[JeremLewis]

You could just diode isolate the ground. It is the same as a relay isolation, but much cheaper (pennies) and cleaner