Grounding Issues with Video Camera/DVR setup

Thread Starter

asprinwizard

Joined Jan 1, 2019
17
Hello,

I wonder if someone might be able to help me out with an issue I am having with a device I built. The device is for use with old Video Cameras which use the standard 10 pin Hirose EIAJ connector: https://www.amazon.com/Hirose-EIAJ-Circular-Male-Connector/dp/B00A0G5N1K

Basic I wanted to a solution to both power and record video from these cameras digitally. So I built a device that gives a 12v power supply from three 26550 batteries, and a PCB with an arduino and a reed relay that deals with the logic of triggering start and stop recording on the DVR device. The DVR device is external, I had hoped to make it internal using a drone fpv recorder but the sound on those devices is very poor. So instead I build an 8 pin mini din breakout socket on the device that can interface with a modified external recorder, e.g. https://www.amazon.co.uk/DIGITNOW-Capture-Digital-Converter-Records/dp/B01DJCDYKI (I added an 8 pin mini din port to this device so I could use a single cable to connect everything).

The breakout cable carries video/audio and the record trigger to the DVR. I'd also like it to carry 5v power to the DVR so I don't have to rely on its internal battery. All is working well, except the power. If I connect up this wire the device is powered from it but there is interference to the audio signal, and on a different DVR, to the video signal. I suspect a ground loop issue somewhere, or perhaps it's just interference from the power wire through the 8 pin din. I'm not sure. But certainly if I use a different power supply to the DVR I don't get the issue. Attached is a sketch of the setup (please excuse the amateur nature of it)

I had one pin for the common ground connection with my device. I tried breaking this up so the AV ground and power ground are separate pins but as they are common in both camera and DVR it didn't make much difference. I've heard of ground isolators and such like, but not sure how they would fit in the setup I have. Would appreciate any advice. One thing I would mention is that while there is no resistance between the av ground and power ground on the DVR in idle state, a small resistance (around 20-40 ohms) does occur when the device is powered on by a separate power source. Not sure where this is from and, as you'll gather, I'm a bit of a noob on these matters.

Please, if anyone can suggest anything to help eliminate the problem I would really appreciate any insight, and I'm obviously rather restricted by the fact that two of the three devices are not easily modifyable.

Thanks very much.
 

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BobaMosfet

Joined Jul 1, 2009
1,108
@asprinwizaard- while your drawing gives an overall 'gist' of connection, we need a slightly better schematic- exactly what components are being used between the larger pieces could be a big help.
 

Thread Starter

asprinwizard

Joined Jan 1, 2019
17
Thanks for your reply. I'm not good at actual schematics but I have done a sketch (attached) the shows the way the components are hooked up. I shall describe it as best I can:

In the middle there is a 9 pin JST socket, this connects directly, pin for pin with the 8 pin mini din, with one of the ground pins also the shield. From the camera video and audio connect directly to the JST. Audio and Video ground (which is common with the main ground) connects to the AV gound pin. The remote rail from the camera connects to the A0 pin on the arduino and is used to determine the recording status. If this changes the arduino sends a pulse from D0 to the reed relay which activates the record switch on the trigger cable which connects through the mini din to the DVR record button.

Powerwise the 12v battery supplies power straight to the camera and through a 5v voltage regulator to supply 5v to the arduino and the power rail to the DVR. There is also an AV out via a 3.5mm jack that comes from the AV out of the DVR back through the mini din/JST to the jack itself.

As I mentioned before I tried to separate the the AV ground from the common ground but tha fact is that once you connect the camera or the DVR these are common on both devices so at that point all ground connections are linked together, which means the JST has three connected ground pins. It wasn't always like this, as I have moved the connections around trying to solve this issue, to no avail.

In order to isolate the problem I stripped back the connections so I just had the AV in/ power and ground but still the issue occurs. The issue itself is that there is a fluttering sound on the audio track, not a hum. On a second DVR (a different model) I get picture interference, with a horizontal line pulsing at the top of the picture. There is also fluttering on the audio on that DVR too. My next step would be to connect the camera, and DVR via a breadboard to see if the issue persists. One thing I have noticed from my experiments is that the 8 pin cable definitely amplifies the issue. So I guess it might just be that the power rail is not well enough insulated from the AV signals. Maybe I need better a better cable? Or a 2x4 core screened cable where the AV and power are separately sheilded? Not sure if this exixts. Would appreciate any input anyone can offer, along with any further things I can try.

Thanks.
 

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