GND vs GNDREF isolation

[IraSch]

How do you intend ground isolation to work? Is there another option other than shorting pins 2&3 on J15?

I can see the need to isolate everything on the "diode" side of the opto-isolators from the rest of the system, but how do you intend to do that?

[taconsultingllc]

For complete isolation between the zones and the remainder of the circuits, J14 and J15 are intended to be in the "isolated" position (i.e. 2&3 for J14 and 1&2 for J15). The schematic is being updated so that both jumpers will be in the same position in the future.

This feature is only intended for externally powered boards. That way the power and ground planes can be isolated from the wESP32 and other logic circuits. I'm working on a manual to aid in understanding the configuration and features of the board.

[taconsultingllc]

If you have any suggestions or features that you think would make this a better product, please feel free to share them with me. I'm working on the third revision and I already have a handful of additional features that I want to add based on feedback from folks like yourself.

Thanks for taking the time to dig in and review the schematics!

[IraSch]

I’m very interested in your project. I currently have a Napco Magnum 850 system from the 80’s (which still works well). I previously added a MKR1000 to it so that if it goes into Alarm, it send SMS texts to me with the status. But the board has no way to arm and disarm other than via the keypads, and they are encoded. So a remote interface isn’t possible as an add-on to it.

I’ve already started on a project very similar to what you have, but since your project is so close to completion, I would be looking at using it instead once it becomes available.

Some of the features I’d be looking for are:

• Ability to use it with 4-wire hardwired smoke detectors. The “detector” part would work as-is with your system, as long as smoke detector zones were always “armed” (unlike burglar zones that would only go into alarm when the system is armed). However, the trick to supporting these detectors is that when the user resets the system, 12V power to the detectors needs to be dropped momentarily. That resets them (assuming the smoke condition is cleared). Heat detectors would work as-is – they aren’t powered – they are either self resetting or designed for one-time use and need to be replaced once they activate.

• I’m sure you already have provisions for battery backup, but that doesn’t help if home power goes down and you lose the internet. So you would need some kind of alarm reporting that doesn’t require a wifi connection. I’m designing for a Particle Boron for notification (alongside the main processor), which could be an add-on to your system (or any other cellular device such as the MKR1500) .It would need to obtain details of why the system activated. Since it is a cellular device, alarms would still get reported to someone/somewhere.

• Some kind of keypad support. I have 3 keypads for my current system, and part of what I developed supports a capacitive touch screen at each location to manage the system (on-screen keypad for PIN entry, on-screen buttons for arm, silence, reset, test, zone history, etc.).

• I’m guessing based on the 3 relays that things like alarm horns or speakers can already be supported. Is there a way for the system to support a different alarm/siren tone for burglar vs fire?

There’s probably more, but these are the first few things that come to mnd.

Looking forward to the final project.

Thanks,

Ira

From: taconsultingllc @. Sent: Saturday, November 02, 2024 4:22 PM To: taconsultingllc/hornet-nest-alarm-panel @.> Cc: IraSch @.>; Author @.> Subject: Re: [taconsultingllc/hornet-nest-alarm-panel] GND vs GNDREF isolation (Issue #2)

If you have any suggestions or features that you think would make this a better product, please feel free to share them with me. I'm working on the third revision and I already have a handful of additional features that I want to add based on feedback from folks like yourself.

Thanks for taking the time to dig in and review the schematics!

— Reply to this email directly, view it on GitHub https://github.com/taconsultingllc/hornet-nest-alarm-panel/issues/2#issuecomment-2453117276 , or unsubscribe https://github.com/notifications/unsubscribe-auth/AEIPWTFCWMGNVDETRG4OAMTZ6UX45AVCNFSM6AAAAABRB2R622VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDINJTGEYTOMRXGY . You are receiving this because you authored the thread. https://github.com/notifications/beacon/AEIPWTEZT23SDFNHMSOU4FTZ6UX45A5CNFSM6AAAAABRB2R622WGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTUSG6MVY.gif Message ID: @. @.> >

[IraSch]

"This feature is only intended for externally powered boards. That way the power and ground planes can be isolated from the wESP32 and other logic circuits. "

I'm 100% with you on this in theory, just don't understand how to make this happen in practice. And the question isn't unique to your system at all.

Assuming the entire system is floating (nothing connected to any ground outside the system) and power is provided via a transformer with secondary windings isolated from utility power, then connecting GND and GNDREF shouldn't be a problem [Note 1]. And any backup battery would be on the 12V side of the system, still isolated.

But if not, then there would need to be 2 totally separate power systems involved. As a practical matter, is this actually ever done in normal alarm system installations?

Note 1: Here's my concern when GND is tied to GNDREF (ditto for 12V & VCC): The sensor wiring constitutes numerous long runs which are essentially antennas. In large installations they could be 100' or maybe more. Is there a risk to the system of picking up stray current from other sources (such as when a 120/240V branch circuit runs next to a sensor run, and a large motor on the branch circuit starts up?

[taconsultingllc]

These are excellent questions, and I'm glad we’re discussing this in detail.

As you’ve correctly noted, in an externally powered setup, it is crucial that the power supply is galvanically isolated, typically achieved through an isolation transformer. The Hornet Nest panel, as you have likely deduced from your inquiry, does indeed incorporate two power supplies.

For most users, the power will likely be supplied via Power over Ethernet (PoE) from the wESP32, which I believe to be the cleanest installation method. However, in some cases, users may require or prefer the additional current supplied by an external power source or have concerns about induced current/voltage. In such cases, the jumpers should be configured for isolation.

In this isolated configuration, the power supplied by the wESP32 adheres to the IEEE 802.3at standard, ensuring galvanic isolation up to 1500 Vrms. If there are concerns about potential induced voltages impacting the system, I would recommend operating the device in the this configuration using both an external isolated power supply and PoE. This setup ensures isolation for the control circuitry while still protecting against stray voltages that may arise from the zones.

You are also correct in your observation that most traditional alarm systems do not utilize two entirely separate power supplies. While such configurations may exist in certain systems, I believe the Hornet Nest Panel to be an exception in this regard.

For additional information about the power availability and galvanic isolation of the wESP32, please refer to the wESP32 Crowd Supply page.