Didier Stevens

I’ve designed and installed my own home automation system: it allows me to control lights and appliances, and monitor activity and environmental parameters at home.

I also have a CCTV DVR with a couple of cameras around the house.

Until now, these 2 systems were not linked. If a PIR sensor detected movement in the garden and later I wanted to see what caused the movement, I had to write down the timestamp and then rewind the DVR around the time the movement was detected. Not anymore. My CCTV DVR has an external IO connector, and now events detected by my alarm system are logged on my DVR. I just have to click on an event on my DVR and the video starts to play.

The problem I faced to achieve this integration, was the lack of documentation. There was no pinout of the external IO connector, not in the manual and not online. So I had to reverse engineer it.

My CCTV DVR is a DVR4L5 sold by Velleman, and is actually produced by AVTECH in Taiwan. The external IO connector is a 9 pin DSUB connector. I can use it to send 4 different alarms to the DVR. But for this to work, the alarm has first to be configured on the DVR:

Set the channel for which you want the alarm to register to N.C. This means Normally Closed, which is counter-intuitive, because I’m using a Normally Open alarm. When I now close the circuit between pin 1 and pin 5 of the external IO connector, an alarm event gets logged and the DVR’s buzzer alerts me. Since I don’t need that buzzer to alert me, I disable it:

Here is an example of alarm events logged by the CCTV DVR:

The DVR can also send alerts to the alarm system. It does this by closing the circuit between pins 6 and 7. For example when it detects movement filmed by one of the cameras. But from experience I know you get a lot of false positives from this motion detection. For example when a cloud moves in front of the sun, the sudden shadow can trigger the simple motion detection algorithm of the DVR. A more useful alert to send to the alarm system is the loss of video signal. The DVR can be configured to sound the alarm when it loses a video signal from one of the cameras. For example when someone tampers with your camera.

Some weeks after I reversed the pinout, I received a reply from AVTECH that confirmed my findings. I’m including it here: