NVR Relay to control gate opening

Discussion in 'General Electronics Chat' started by Tom Edwards, Jun 1, 2016.

  1. Tom Edwards

    Thread Starter New Member

    Jun 1, 2016
    Hi there,

    I install CCTV systems and have had a request to install a NVR recorder, with the ability to open/close an electronic gate. Close to the NVR, there is a switch that the operator presses when on site, one button to open, one to close and an emergency stop. I have linked to a diagram showing all of this below.

    I believe that the gate relay uses a 24v circuit. There are 4 outputs on the NVR that I can switch off and on, they are labelled 1, G, 2, G, 3, G, 4, G I understand that they are volt free, dry relays.

    The button uses an NO circuit to open, another to close the gate, plus a NC as the emergency stop.

    I am unsure if I need some other type of relay to go inbetween the NVR and the switch to achieve the above, perhaps someone could recommend something? It would be really appreciated!

    https://www.dropbox.com/s/ypdq3c2kdtq7jt8/switch diagram.jpg?dl=0

  2. Tonyr1084

    Active Member

    Sep 24, 2015
    Hi Tom; and welcome to our forum.

    I'm not sure what an NVR recorder is. Being that you install these things, professionally I'm assuming, you know more about DVR's than I do. So I may be off base on this but -

    OK, my DVR has an alarm output. Whenever it senses motion it starts recording 5 seconds before the motion occurred. (at least 5 seconds of video is always retained in memory so that when the motion is detected the recording can start 5 seconds before hand) My DVR also will send an alarm signal out, but that's a feature I don't use.

    If I wanted to do something like what you're asking for I'd use my DVR (which will record for up to 5 minutes after detecting motion) and use the alarm signal to open the gate. After the video times out the alarm goes away and that can be used to trigger gate closure. HOWEVER - if the sensitivity is set too high anyone could walk up to the gate and it will open. And my DVR is always going off when it snows or when a bug flies past the camera. Shadows from birds triggers it too.

    I probably wouldn't do this (what you seek). Having a smart person as a detector is better than a sensor. What happens if a child wanders into the gate and the camera does not trigger (or cancel the trigger) and the gate closes on them trapping them and possibly choking them to death. And with the camera there would be no one to hit the emergency stop button. Just how you would control that part of the detection system - I haven't any ideas.

    It would be nice to automate the system, like a garage door opener that will stop the door from closing if something breaks the beam or if the motor senses an obstacle blocking the door. But what's the purpose of a gate if anyone can walk up to it and have it open for them? May as well not have a gate at all. And since a dog - or a leaf or a shadow of movement can trigger (MY) DVR, the gate would be opening and closing all the time. Honestly, I think this is not a good idea. But the solution would be interesting to hear when you come up with it.
  3. ifixit

    Well-Known Member

    Nov 20, 2008
    Hi Tom,

    Read the documentation that comes with the NVR (Network Video Recorder) it should explain how to use the "Gn" outputs. It sounds to me like you can just wire G1 across the OPEN switch, G2 across the CLOSE switch and EMRG STOP switch across G3. The NVR software would have to allow you to program each of the outputs as either NC or NO. Use a battery and lamp to test how they work to be sure you have everything setup correctly.

    I assume the operator will view the live video stream online and then activate the appropriate switch remotely depending what he sees at the gate.