USB ground and chassis ground

PsyKotyk · Post by **PsyKotyk** » Tue Mar 11, 2008 6:49 am

I noticed in the manual, and the sticker on the ECU that it says not to allow USB ground to come in contact with chassis ground.

What is the reason for this? I have a in car PC, and touch screen LCD in the dash that I would like to run KManager on, but I don't want to be shorting out the daughter board. My Car PC (a mini-itx/voom setup) is definitely chassis grounded.

Any plans for an opto-isolated version in the future?

Post by **Hondata** » Tue Mar 11, 2008 9:09 am

The reason is that if the main harness ground (normally to the intake manifold) is no good, then the USB ground will sink a huge amount of current. Also it seems that if in doubt many people add inappropriate grounds all over the place, where often that causes problems.

If your main harness ground is good then you should not have any problems. If in doubt check current flows with a multimeter.

USB cannot be optoisolated.