Retronetworking

h1. Nokia EKSOS N20 DIY carrying case

In preparation of the first hacker event where we wanted to offer ISDN Uk0 service (see [[ISDN_at_CCC_Camp_2023]]) we wanted to build portable, self-contained and ruggedized systems from the Nokia EKSOS.

The systems should contain

* EKSOS N20 shelf with mandatory NCU and some subscriber line cards

* a number of  subscriber ports broken out to RJ45 connectors

* a 48V power supply

* an [[Osmocom_icE1usb]] plus an embedded Linux board to run TDMoIP for the V5 back-haul

** should have at least two Ethernet ports so we can also back-haul the Q3 management interface to a remote location

* some fans for active cooling as it is getting rather hot in the sun outdoor on a camp

* ruggedized enclosure to make sure the equipment survives transportation unharmed

h2. Enclosure

The enclosure is made of wooden panels.

h3. wood corpus

h4. Assembled enclousre body

!20230801_203832.jpg!

h4. Milling left and right sides to accomodate screw heads

Unfortunately the EKSOS shelf mounting flanges contains a number of screw heads and other protrusions, which require the side panels to be milled

!20230801_203546.jpg!

h4. Bottom side / gliders

!20230801_203821.jpg!

h3. Fans / Cooling

h2. Power Supplies

The power supplies are mounted in the rear part of the bottom panel

!20230804_192817.jpg!

h3. 48V: MeanWell RSP-150-48

This supply is used for powering all 3 rails of the EKSOS shelf:

* odd numbered line cards

* even numbered line cards

* signaling voltage

I've used the trimmer potentiometer to trim the output voltage to the maximum (+5%).

h3. 12V: MeanWell RSP-12-35

This 12V supply is used to power the nanoPi R5S as well as the fans.

h2. Subscriber port break-out

Initially, I started with a 1U RJ45 ISDN patch panel at the bottom of the enclosure. Later, I switched to a PCBA + IDC ribbon cable approach to reduce the amount of manual labour.

h3. Original approach: ISDN patch panel + wiring

This approach was implemented in the first two units.  It consists of

* a 50-port 1U ISDN patch panel mounted to the bottom of the rack

* three telephone cables of each 16x2x0.6mm

* three DIN connectors

* lots of heat shrink tube 1.6mm

!20230805_090346.jpg!

h3. Updated approach: Ribbon cable, IDC connectors + custom PCBA

The idea of this approach was to 

* build a custom break-out PCBA which can be slided into the EKSOS shelf (removing a subscriber line card)

* build a ribbon cable with IDC connectors towards the EKSOS subscriber line card (DIN connector) and a 64pos 2-row header (break-out board)

h4. break-out PCBA

The boards has 16 RJ45 connectors.  The center two pins (4+5) are routed to the first (left) IDC connector.  The two surrounding pins (3+6) are routed to the second (right) IDC connector.  This allows a single break-out board to carry either 16 or 32 subscriber ports.

!20230811_120723.jpg!

h4. ribbon cable with IDC connectors

!20230811_120736.jpg!

h4. break-out PCBA with IDC ribbon cable plugged in

!20230811_120809.jpg!

h4. subscriber line cards + breakout boards installed in rack

!20230811_140854.jpg!

h2. icE1usb + Linux SBC

Given that we needed multiple Ethernet ports in a Linux SBC with passive cooling, there weren't really all that many options on the market.  I went for a *nanopi R5S*, which has 3 ethernet ports.

h3. nanoPI R5S 12V DC re-work

For some weird reason, the nanoPi R5S *only* supports USB-PD.  There is no straight DC supply connector for feeding e.g. 12V to it.  Not even an unpopulated header on the circuit board.

This meant that it simply wouldn't power up at all if 12V were applied from the 12V mean-well power supply in the unit.  Luckily, @tnt and I came up with some hardware re-work to modify the R5S to accept a 12V DC input without any USB-PD signaling:

FIXME: Describe the rework

h4. Unmodified R5S

!20230809_233333.jpg!

h4. R5S with removed resistor

!20230809_233308.jpg!

h4. R5S with additional pull-up resistor

!20230809_233231.jpg!