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JPuma · 09-12-2005, 10:22 AM

I have been pondering this some more and dont undstand why this works compared to other methods I tried. I mean, when I use an inverter on the LCD I didnt see the noise but when I used the cars unregulated power I did see the noise; two seperate power sources to the monitor. The only difference is the cars power also powers the P1900. In both senarios they both are still grounded by the same ground but in the monitor its through the USB and monitor cables.

Also if this is a power fluctuation thing then why does it go away when I power the PSU for the computer with a different 12V power source (tank battery alone). There something more going on here then just power fluctuation from the computer. I think its more like feedback on the power line, or maybe freqency noise on the power line given off by the computer (same thing?). Is there a way to check this using an oscilloscope? if so isnt their a filter that can fix this?

not sure why the PSU's 12V is able to filter this out, maybe its desigend to. Is it possible that the computer is pulling down the 12V car power in such small doses that it doesnt hurt the anything but can be seen in the monitor, sort of like theres AC on the line? (god, I wish I continued passed ohms and voltage law in tech school).

How this for a theory, what if we put a diode on the 12V line feeding the PSU, if theres any power "feeding back" on the 12V line from the computer then it wont infect the entire 12V system in the car? If its frequency thats feeding back, wouldnt there be a way to filter this? mind you, this is all speculation and I may be way off base. Maybe this will prompt someone who is EXTREMELY knowledgeable in this are to speak up.

For me the problem is solved but what if I want to add more monitors in the foreseeable future (headrests?) If the 12 line in my PSU cant handle them all I will need to look for another power source and I dont want to use an isolated power/inverter solution. Also, it would be nice to use my OBM now in conjunction with the VGA.

09-12-2005, 10:22 AM	#7
JPuma Constant Bitrate Join Date: Jul 2005 Location: NY Posts: 213	I have been pondering this some more and dont undstand why this works compared to other methods I tried. I mean, when I use an inverter on the LCD I didnt see the noise but when I used the cars unregulated power I did see the noise; two seperate power sources to the monitor. The only difference is the cars power also powers the P1900. In both senarios they both are still grounded by the same ground but in the monitor its through the USB and monitor cables. Also if this is a power fluctuation thing then why does it go away when I power the PSU for the computer with a different 12V power source (tank battery alone). There something more going on here then just power fluctuation from the computer. I think its more like feedback on the power line, or maybe freqency noise on the power line given off by the computer (same thing?). Is there a way to check this using an oscilloscope? if so isnt their a filter that can fix this? not sure why the PSU's 12V is able to filter this out, maybe its desigend to. Is it possible that the computer is pulling down the 12V car power in such small doses that it doesnt hurt the anything but can be seen in the monitor, sort of like theres AC on the line? (god, I wish I continued passed ohms and voltage law in tech school). How this for a theory, what if we put a diode on the 12V line feeding the PSU, if theres any power "feeding back" on the 12V line from the computer then it wont infect the entire 12V system in the car? If its frequency thats feeding back, wouldnt there be a way to filter this? mind you, this is all speculation and I may be way off base. Maybe this will prompt someone who is EXTREMELY knowledgeable in this are to speak up. For me the problem is solved but what if I want to add more monitors in the foreseeable future (headrests?) If the 12 line in my PSU cant handle them all I will need to look for another power source and I dont want to use an isolated power/inverter solution. Also, it would be nice to use my OBM now in conjunction with the VGA. Last edited by JPuma; 09-12-2005 at 10:29 AM.