LED across input zone

[Ira]

I know this sounds weird, but...

I have some LED's with the following characteristics...

Forward voltage: 12V
Forward current: 13mA

If I want a cheap, easy, external indicator of a zone's status (i.e., the LED mounted externally), can I connect one of these to the zone's terminals on the M1G input zone expander board? If I can do so withoug affecting the M1G, what would happen with the LED when the zone is open and when it is closed if the zone is defined as normally open? Does the opposite occur if the zone is defined as normally closed?

Thanks,
Ira

 

[JimS]

I know this sounds weird, but...

I have some LED's with the following characteristics...

Forward voltage: 12V
Forward current: 13mA

If I want a cheap, easy, external indicator of a zone's status (i.e., the LED mounted externally), can I connect one of these to the zone's terminals on the M1G input zone expander board? If I can do so withoug affecting the M1G, what would happen with the LED when the zone is open and when it is closed if the zone is defined as normally open? Does the opposite occur if the zone is defined as normally closed?

Thanks,
Ira

Probably not. The LED will likely load the zone and cause problems with sensing the status of the zone. You might measure the voltage at the zone terminals with the zone open and closed and use a transistor or FET to buffer the voltage. But this would require another source of voltage - if your cable has extra wires you might be able to get it from the panel.

 

[mustangcoupe]

Probably not. The LED will likely load the zone and cause problems with sensing the status of the zone. You might measure the voltage at the zone terminals with the zone open and closed and use a transistor or FET to buffer the voltage. But this would require another source of voltage - if your cable has extra wires you might be able to get it from the panel.

While I do agree with JimS, you might be able to use EOL resistor setting and by changing the standard value of the resistor and adjust it so the LED and the Resistor will still look like the standard EOLR

 

[Del91574]

The output boards are really cheap, though not compared to a straight LED. I'd be more worried about the zone not functioning as intended, especially if it's being used for a security application.

 

[apostolakisl]

You can't harm the Elk by putting the LED accross the zone. From the Elk's perspective, the LED will look like a resistor. The question is, how much resistance. Try just hooking the led directly up to one of the zones.

Check for:

1) does the led light up. If not, forget it. There isn't enough current and no need to go further.

2) If it lights up, look at your ElkRP status section and see what voltage is reading. If you are using EOLR then the system is looking for around 6 or 7 volts. If it is much less than that, forget it, the led resistance is too high. If it is higher than that, you can add another resistor of appropriate size to drop the voltage to around 6 or 7 volts.

If the LED should fail (burn out), then the zone would show open circuit (the same as if the door/window is open). If the led fails as a short (unlikely), the voltage would drop and the Elk should show a fault as well. This one will depend on just how much resistance the led provided versus how much your secondary (if needed) resistor provided.

I really don't see a security issue here except that potentially your eolr would become not needed in which case you would lose the benefit of it (unless the led were located where you would put the eolr, but that seems unlikely).

 

[Del91574]

The OP and others can do as they want, however I was commenting on what I believe would be a compromise in the overall security of an alarm panel and protective zone. A diode is not an EOLR, nor do they perform even remotely close to the same electrically.

DIY and homebrew can do as they want, but if something happened in my case, the insurers would have a field day with a protective circuit installed in a manner not dictated or I/A/W the installation instructions. If for an automation zone status, then so be it, experiment, but for a burglar alarm zone, I'd avoid it.

 

[Ira]

It's an automation project. The M1G zones correspond to irrigation system valves. When power is going to a valve, the N/O zone will close. Since my irrigation controller project is getting pretty complex (including physically/electrically isolating the valves from the controller using wireless mirror relays), I thought it would be nice to have an external indication near the control panel/can that power is going to the valve(s).

 

[Ira]

I ran a test using the LED previously described. I connected it directly across the zone terminals for a zone on an M1XIN zone expander. The zone is defined as normally open, non-alarm.

Before connecting the LED, Elk RP showed...

Status: Normal
State: Open (+)
Volts: 14.0

After connecting the LED, Elk RP showed...

Status: Violated
State: EOLR (=)
Volts: 5.2

I left the LED connected for a couple of minutes. It didn't heat up at all that I could tell by touch.

If I were to put this into use, there would be a N/O relay involved. The LED would be wired in series with the relay. So, I would wire one of the M1XIN zone's terminals to one contact on the relay. The other relay contact would be wired to one of the LED leads. The other LED lead would be wired to the other M1XIN zone's terminals (keeping in mind the polarity of the LED).

So is Elk RP trying to tell me this is okay? Why is it showing the state as "EOLR (=)" when I have the zone defined as normally open? Is it because the LED isn't letting all the voltage thru like a simple contact closure would, so it thinks there is an EOLR present?

Thanks,
Ira

 

[BraveSirRobbin]

Do you currently have an EOL resistor in place?

 

[Ira]

Nope. The zone is currently unused. Nothing is connected to it until I connect the LED.

Also, nothing unusual showed up in the Elk log while I performed the test.

 

[Del91574]

I ran a test using the LED previously described. I connected it directly across the zone terminals for a zone on an M1XIN zone expander. The zone is defined as normally open, non-alarm.

Before connecting the LED, Elk RP showed...

Status: Normal
State: Open (+)
Volts: 14.0

After connecting the LED, Elk RP showed...

Status: Violated
State: EOLR (=)
Volts: 5.2



So is Elk RP trying to tell me this is okay? Why is it showing the state as "EOLR (=)" when I have the zone defined as normally open? Is it because the LED isn't letting all the voltage thru like a simple contact closure would, so it thinks there is an EOLR present?

Thanks,
Ira

The panel is seeing the load of the LED and it's looking for either 14 volts for an open or NO circuit or 0 V for closed. 5.2V represents a partial short to the panel. Changing the circuit type won't make a difference either. The only thing you'd be able to do is figure out the LED's resistance or current limiting resistor and/or bias your own circuit to provide the voltages the panel needs to see to accurately represent all 3 states, open, secure, and violated.

Is there a reason why the onboard triggers on J16 are being avoided or installing a XOVR to give you both relays and triggers? It'd really make things easier to make work without reinventing the wheel.

 

[apostolakisl]

If you are getting 5.2 volts at the ElkRP, then the resistance of the led you are using is slightly more than an EOLR. If the Elk doesn't know what to do with that value, I suggest running another resistor in parrallel with the led. On average, the resistance of the led and the resistor you put in parrallel would need to be equal to the resistance of a standard eolr.

Or, you could try a different led that provides less resistance.

And, yes, if you are a commercial installer doing a security system, you should not fudge the rules, even though the physics of this is fine, lawyers are all about rules and regulations, and sadly, the lawyers seem to rule the world.

 

[Del91574]

Resistor in parallel would affect the current as well, creating another issue with possibly being able to even light the LEDs he has up, the amperage available would decrease with another resistor.

 

[Ira]

I agree that using an M1XOV or M1XOVR would be a good way to do this, but that would require two boards at close to $100/board (I have more than eight zones), take up space in the can (which is already crowded), use quite a few of the maximum 208 outputs, and take an additional two rules per zone. I'm not sure it's worth the additional costs (monetary and otherwise) for this particular objective.

Another approach would be to change out the SPDT relays that act as "sensors" for the M1G zones to DPDT relays and use the additional set of contacts with a 12Vdc power supply daisy-chained to each of the relays to power the LED's.

Ira

 

[apostolakisl]

Resistor in parallel would affect the current as well, creating another issue with possibly being able to even light the LEDs he has up, the amperage available would decrease with another resistor.

I bet it would still light up. You don't need to shunt much current to lift 5.2 to 6.something.