The install video for this product (https://konnected.io/products/konnected-alarm-panel-interface-module) shows to connect this interface zones in parallel to existing zones (https://youtu.be/fcY0dYuBQCo?t=760)

I'm wondering how the interface does not interfere with the zone (I'm new to electronics). If the interface connects to existing zone + terminal, it effectively creates a parallel circuit with the sensor right? The panel monitors the zone resistance to decide if the zone is violated or tampered, but adding the interface in parallel surely must change the resistance being monitored? If that is the case and the interface potentiometer is what caters for this, then how would it work if a zone is violated?

If the zone is violated on a NO (with its own resistor in parallel) sensor the interface would see a huge reduction in current I guess? Does the interface watch for current then?

But if the zone is violated on a NC sensor (with its own resistor in series) the interface would see higher current? Since the interface is in parallel and the sensor side is open, how would the interface know the zone is violated?

If the interface is monitoring voltage and not current, how would it know about zone violation given that parallel circuits have same voltage even if one branch (the sensor) is opened?

I'm confused about how the interface works electrically while not interfering with the zone on the panel side.

Any insights appreciated, thanks.

7 hours ago, h1771t said:

The install video for this product (https://konnected.io/products/konnected-alarm-panel-interface-module) shows to connect this interface zones in parallel to existing zones (https://youtu.be/fcY0dYuBQCo?t=760)

I'm wondering how the interface does not interfere with the zone (I'm new to electronics). If the interface connects to existing zone + terminal, it effectively creates a parallel circuit with the sensor right? The panel monitors the zone resistance to decide if the zone is violated or tampered, but adding the interface in parallel surely must change the resistance being monitored? If that is the case and the interface potentiometer is what caters for this, then how would it work if a zone is violated?

If the zone is violated on a NO (with its own resistor in parallel) sensor the interface would see a huge reduction in current I guess? Does the interface watch for current then?

But if the zone is violated on a NC sensor (with its own resistor in series) the interface would see higher current? Since the interface is in parallel and the sensor side is open, how would the interface know the zone is violated?

If the interface is monitoring voltage and not current, how would it know about zone violation given that parallel circuits have same voltage even if one branch (the sensor) is opened?

I'm confused about how the interface works electrically while not interfering with the zone on the panel side.

Any insights appreciated, thanks.

Normally Closed (NC) sensors are closed in standby. Alarm panels usually use End-of-Line Resistors to monitor zone resistance normall ~ 2k ohm. When alarm sensor is open = infinite resistance.Tamper, short or wire-cut the resistance is outside of the expected range.

The panel constantly measures voltage across the zone via pull-up/down resistors or internal ADCs(analog to digital converters) to decide the zone state.

Here's how these interfaces typically avoid interfering with the panel. High Impedance Voltage Sensing. The interface doesn't draw any meaningful current it behaves like a voltmeter across the zone input. Since the voltage across the zone changes depending on whether the circuit is intact, open, or shorted, the interface can just observe the voltage level and because it has very high impedance >100kohm input resistance it doesn’t affect the total resistance the panel sees which is usually around 2k ohm.

So yes, the interface reads voltage, not current. This avoids all the resistance-parallel concerns.

Edited June 21, 20251 yr by TaliaB
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Thanks for the info. Some questions:

• How would the interface pick up voltage changes? If the interface is parallel to sensor, and the sensor is opened to open circuit, voltage on the parallel interface would not change right? (voltage remains same over parallel circuits). Say the panel pushes 12v (I'm guessing), the interface is parallel so if the sensor is open or closed, interface still gets 12v?

  I wonder if there's a circuit diagram somewhere that can assist me to see how it's working. Maybe I'm not understanding your comment about pullup/pulldown or ADC.

• Why would the interface work over both NO and NC sensors?

Thanks!

You're right. I'm getting confused seeing the circuit diagrams of basic series circuits with batteries, which are constant voltage, and assuming the zone circuit is constant voltage, which it isn't.

I measured the voltage on some closed zones at 2V, and an open zone at 5V. I guess these zone circuits are then constant current circuits?

Also the interface developer confirmed what you said in a nice and short summary here: https://community.konnected.io/t/how-does-the-konnected-alarm-panel-interface-module-work-electrically/39881/2

Thanks again for the info