Communication Problem

marklamond · Post by **marklamond** » Wed Aug 01, 2007 5:14 pm

Hi there,

I'm having a problem with my S300 and Dell Latitude C640.

I bought a DC-DC converter to use with the laptop but every time i connect it to the laptop i loose communication with the S300. The lights on the S300 flash away as normal when datalogging but as soon as you fire up the DC-DC the red light goes out and you have a solid green. To re establish comms you need to un-plug/re-plug the USB connector.

When running from battery everything is fine.

I would normally suspect some sort of ground loop, as the ground is connected straight through on the DC-DC but i can't find anything unusual just yet. If i cut the + feed to the DC-DC leaving the ground still coupled through i don't have a problem, but the DC-DC obviously isnt running.

I'm going to take a serious look at it tomorrow, i can't see any unusual current flow in the USB +5v or GND between the laptop and S300 or differences in potential before you hook them up.

I just wondered if anyone else had encountered similar issues before i spend a load of time on it.

Cheers,

Software: 1.2.7.0
Firmware: 1.03

Post by **Spunkster** » Thu Aug 02, 2007 9:29 am

You are probably generating a large amount of EMI and that is what is causing the problem datalogging.

marklamond · Post by **marklamond** » Sat Aug 11, 2007 7:25 am

Yeah, i wouldnt expect the converter to be cleanest thing. I put it on the scope and fed it from a professional bench supply.

I didn't expect it to be this bad though, its a wonder it didnt damage the laptop! I opened the converter up and it is a complete piece of junk.

I dug out an old converter and had a look at it, this is about what i would expect for a ?25 converter - the S300 is fine with this one.

I'm going to get one of those APC combo AC/DC input supplies and see how that goes, i would expect their stuff to be well designed. It would be useful to only have to carry one supply around.