USB isolation

trueppp · 12-12-2007, 02:06 AM

Hi,

Okay guys, i got a good one for you, first of all my setup: compaq laptop, powered by inverter, sound by onboard sound card to wired FM modulator(sound quality is EXCELLENT).

everything was going fine till i dicided what the heck, im gonna buy a touchscreen, so i wire the whole thing up and now kaboom, when i plug un the touch screen cables (USB &/or VGA) i get alternator whine (changes w/ revs, yet voltage stays constant), its less pronounced when i have music on full blast but i get tired of reaching for my headunits volume dial under the screen.....is there anyway to isolate these lines????(ps problem is less significant if i unplug one of the two but still present and rerouting was without avail)

thanks

dan

Felix509 · 12-12-2007, 08:20 AM

A few things to check:

Is your Touch screen powered form the cig lighter outlet? May need to power and ground from same place as computer is.

Is your USB cable running alongside power cables? If so the 12V may leak into it.

May need a higher quality USB cable with better shielding..

Just to test, with the car running where you can hear the Alt whine, move the USB cable around to see if the Whine goes away/gets louder. May just need to relocate this cable..