[time-nuts] 5370 processor boards available

John Seamons jks at jks.com
Wed Oct 8 13:40:56 EDT 2014

On Oct 8, 2014, at 8:00 AM, Chuck Harris <cfharris at erols.com> wrote:

> Is removing the HPIB connector "the way"?
> Is anyone making a replacement panel that has a USB
> and an RJ connector mounted?

I have looked into the mechanical issues of doing that, but haven't done a PCB layout yet.

My plan was to include a USB isolation chip on the board so the USB connection has as much galvanic isolation as the transformer-coupled Ethernet. Also, I wanted to add a regulator to supply +5 on the internal side of the USB, driven from one of the large caps of the HP supply. That would provide some hold-up power for orderly shutdown of the Beagle on 5370 power-off. Alternatively, there would be some jumpers so the USB could bypass the isolator so the USB power could be supplied full-time from an external USB charger. That way the Beagle would run continuously for an "instant on" experience on 5370 power-up.

There are some EMI/EMC and ground loop issues with all this. My guess is that if you use shielded Ethernet cable the shield/drain wire, and the shield/gnd wire of the USB,  should probably be left floating on the 5370 end (i.e. non-shielded USB/RJ45 connectors on the PCB or making sure shielded connectors are isolated from the back panel). But I am no expert with such issues and would appreciate any advice. I kinda like PHK's solution: use a hole to get the cables out of there as quickly as possible.

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