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Feature #5624

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Bug #5542: Move hub to datacenter colocation

design / prototyping / testing of icE1usb RS485/422 daughterboard

Added by laforge 23 days ago. Updated 3 days ago.

Status:
New
Priority:
Normal
Assignee:
Category:
hardware
Target version:
-
Start date:
07/22/2022
Due date:
% Done:

0%


Description

The idea is to have a board with 3x RS422/485 drivers/receivers.

For the "OCTOI hub" situation, we'd need
  • 1x Rx NMEA
  • 1x Rx 1PPS
  • optionally: 1x Tx NMEA (no use case for it right now)
For the "DUG/DUL GPS source" use case, we'd need
  • 1x Tx NMEA
  • 1x TX 1PPS
  • optionally: 1x Rx NMEA (not 100% certain it's needed, but recommended)

The ISL83485 (switchable direction) I used in the siu-clock-breakout is sadly not available right now, but I'd hope some other driver circuit is.

Actions #1

Updated by laforge 4 days ago

I don't want to put any pressure on you, tnt, but I was wondering what the estimated schedule would be for this? To avoid extra travels of ~500km one way to the data centre, I'd want to piggy-back the deployment on a trip on September 19, 2022. And prior to that, the system with the GPS02 shoul be tested at my home. Is that realistic?

Would it help if I did that daughterboard hardware design?

Actions #2

Updated by tnt 4 days ago

Yeah sorry, that actually completely slipped my mind.

The ISL83485 is also non-isolated. I'd rather use something that's completely floating and allows high potential difference since they'll be very far appart and the GPS02 will most likely be grounded/referenced at the install site on the roof.

I'll have a look at what chip I can find that's available.

Actions #3

Updated by laforge 4 days ago

On Wed, Aug 10, 2022 at 11:48:37AM +0000, tnt wrote:

Yeah sorry, that actually completely slipped my mind.

no worries. We were waiting for answers from the colocation for a long time earlier.

The ISL83485 is also non-isolated. I'd rather use something that's completely floating and allows high potential difference since they'll be very far appart and the GPS02 will most likely be grounded/referenced at the install site on the roof.

The GND situations is as follows:

  • GPS02 SMA shield, metal enclosure and the GND line on the RJ45 are DC-connected inside GPS02
  • GPS02 enclosure is mounted on DIN rail, which is connected to Earth/PE in the cabinet on the roof
  • The 12V which we supply from the rack side is of course free floating, no PE/Earth connection there
  • The 5V/GND powering the icE40 is provided by some PC, which typically connects GND to chassis/PE in the rack

So indeed, the GND = PE on the roof and the GND = PE in the rack might have
significant voltage difference due to the 100m in between. So the differential
signals in rx vs tx direction might center around some different voltage.

Not sure what DIN regulations say about voltage difference on PE within a single
building. Having isolation is of course good.

I'll have a look at what chip I can find that's available.

Actions #4

Updated by tnt 3 days ago

Just ordered parts to build 3 of them.
Still need to do the schematic / layout, but the mains components/design is done.

It uses separate digital isolators chip and rs422 tranceivers.
The isolated section will be powered from the 12v pins through a 5V regulator.

Actions #5

Updated by laforge 3 days ago

On Thu, Aug 11, 2022 at 10:29:28AM +0000, tnt wrote:

Just ordered parts to build 3 of them.

thanks!

It uses separate digital isolators chip and rs422 tranceivers.
The isolated section will be powered from the 12v pins through a 5V regulator.

that's fine. So from outside the icE1usb we'd then feed the same 12V to both the
daughterboard and the GPS02.

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