With some of the Hikvision camera range there is an S option which gives Audio and Alarm I/O capabilities. Frustratingly I have been unable to find detailed information online or in the manuals on how these work so I bought one and had a play.
An example of such a camera is DS-2CD2532F-IS which comes with a pigtail cable with a green connector block. This has four screw down connections labelled from left to right as I, O, GND and A.
View attachment 582 Click to enlarge the picture
The narrative below explains what each of these are and how they can be used.
I : Alarm Input
This allows an external device to tell the camera to start recording. An example of such a device could be a PIR which might be used in preference to the camera's motion detection which is notoriously sensitive to changes in sun, clouds, heavy rain and lightning flashes.
The alarm input can be triggered by simply shorting the I input to GND (ground) as could be done by a simple on off switch - you do not need to feed any power into it.
Of course if you wish to use a PIR you will need to feed the PIR with power in order for it to function and switch the alarm input. Irritatingly there is no power output available on the DS-2CD2532F-IS which means potentially means a separate power supply and cabling.
If instead of using POE (Power Over Ethernet) you are running a power cable to the camera (it has a power connector for non-POE users) you could tap in to this for low voltage power using a CCTV power splitter cable which you can source on ebay or on specialist CCTV web sites . Just make sure you have checked the voltages and power consumption of the devices you want to power are compatible with the power supply you have bought to power the camera. Most of the HikVision IP cameras are 12V but I found one that was 24V.
Remember you will need to configure in the camera whether the alarm input is expecting Normally Open (NO) or Normally Closed (NC) connections along with a schedule of when the camera should accept such inputs or ignore them. NO connections are basically like an on-off switch where the switch is normally OFF and when something like a PIR detects movement it is switched to ON. NC connections on the other hand are basically like an on-off switch where the switch is normally ON and when something like a PIR detects movement it is switched to OFF.
If you are going to use a PIR you may want to consider a 12v one designed for an alarm system as the better ones are much more advanced (less likely to give a false alarm) than the mains powered ones used to switch outdoor lights. Also if using the PIR outdoors make sure it is rated for outdoors use. I found this article quite helpful as it gives you an idea of the outdoor PIR types available and who makes them
The downside is that these don’t come cheap and they can be quite large.
If like me you use Synology Surveillance Station to control and monitor your cameras do be aware that alarm inputs alerts are tagged differently from motion detection alerts and so you have to explicitly configure Surveillance Station to trigger on these (SS> Management > IP Camera> edit camera > schedule). I lost a day and some hair before I found this out...
A : Audio Output
This allows you to feed an audio signal into an amplifier and then to a loudspeaker. You cannot attach a speaker directly to the camera. The audio will come from a microphone attached to a PC which is then routed over the IP connection to the camera. With the DS-2CD2532F-IS it has a built in microphone so this setup would allow a CCTV operator to have a conversation with someone near the camera which would be useful if it were located near to an entrance door. The camera's Live View page on its web interface is one way of using this capability.
While I have not used the audio output it would be my expectation that you would feed the amplifier's input with the A and GND outputs. Remember you will need to use screened audio cable to prevent noise. Given the size of the screw down connectors make sure you use a small diameter cable.
Again you would have to feed power to the amplifier.
For testing purposes you may want to play with the camera indoors and try and feed the audio into an external audio input on a TV or portable radio or a music player dock. For a more permanent solution you should be able to find suitable low powered amplifiers and loudspeakers at the likes of ebay, or Maplin in the UK, or Radio Shack in the US. Search for “Mono audio amplifier” or “amplified speaker mp3”. Make sure you get something which allows you to adjust the volume (gain). If you are going to use the speaker outside (even if under cover) then you need to make sure it is rated for outdoor use otherwise you will end up with some very soggy cardboard that will fall apart.
O : Alarm Output
This allows you to signal an alarm condition to an external device if say the camera's motion detection has spotted a movement.
With regard to the alarm output (O and GND) be very careful. I have not played with it and don't know for sure how it works let alone what the voltages are and what the maximum output current is. I suspect you can directly hook this output to alarm panels and to CCTV recording devices, but whether you can connect it directly to things like Raspberry Pis I do not know. You certainly will not be able to connect anything like a light bulb or a buzzer without using a relay. How you wire relays up so they do not damage the circuitry in the camera is outside my area of expertise although the words
Back EMF and
Diodes ring distant bells in my head.
If anyone has expertise on the above please do comment as I would be interested.
GND : ground
This is used in conjunction with the above connections to complete the circuit.
Hope this information helps a little and that I haven’t made too many mistakes. Do keep in mind you use this information at your own risk. I am not an electronics expert so I don’t warrant its accuracy.
(Nothing personal)
